Prey capture by Dionaea muscipula- A review of scientific literature with supplementary original research

Abstract

Many descriptions of prey capture by Dionaea muscipula (Venus flytrap) in popular publications and educational literature are inaccurate. Here we review well documented literature on prey capture in this plant’s natural habitat and add observations on prey capture and attraction mechanisms we have observed in plants cultivated in a greenhouse and garden.
Despite its common name “Venus flytrap” does not specialize in capturing flies. About 70% of the prey it captures in its native habitat consists of spiders, ants, and beetles. Flies are only one- to-eighteen percent of what it captures. In a greenhouse where flies, capable of entering the vents, composed most of the available prey, over 90% of the prey captured were flies. Dionaea cultivated in a garden captured a diverse array of animals, only about 37% of which were flies. Dionaea is a generalist, capturing a wide variety of prey species. Its capture mechanism does not appear to have a “syndrome” analogous to the Pollination Syndrome in flowers where a specific floral type is pollinated by a specific animal (i.e. Bee Flowers or Fly Flowers).
The measured capture rates of Dionaea are low, about one capture/leaf/month in its native habitat. Similar but lower rates were measured in the greenhouse and garden. The single measurements in each habitat need to be repeated, but the low rates are consistent with the observation that wherever it is observed Dionaea has nearly all of its traps open. Both the low capture rates and the large number of open traps suggests that alluring agents drawing prey either do not exist or are ineffective.
Despite reports of nectar secretion by Dionaea traps, our observations show that unstimulated traps are always dry unless wet by rain, condensation, or a sprinkler system. Secretion occurs only after prey capture. Alluring glands along the outer trap margin have been reported to be visited by small ants that work their mouthparts over the glands. We have photographed a fly exhibiting the same behavior. The exact nature of this behavior needs to be further investigated, but it does not appear that this attractant can act at a distance since flies are as likely to land on the outside of a trap as on the inside.
Darwin proposed that the trap closure mechanism allows small prey to escape, preventing the expenditure of energy on captures likely to be of little benefit. Recent measurements of prey captures indicate that traps show little selectivity based on prey size and that while traps could, in theory, select larger prey, statistically they do not behave this way.

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44 Carnivorous Plant Newsletter
Technical Refereed Contribution
Prey capture by
Dionaea muscipula
A review of scientific literature with supplementary original research
Stephen E. Williams • Emeritus Professor • Lebanon Valley College • Annville • Pennsylvania
17003 • USA • williams@lvc.edu
Siegfried R. H. Hartmeyer • Weil am Rhein • Germany • s.hartmeyer@ t-online.de • www.
hartmeyer.de
Keywords: Dionaea muscipula, Venus flytrap, habitat, prey attraction syndrome, alluring glands,
nectar secretion, red color, scent, UV-reflection, fluorescence, size selection, capture rate.
Abstract: Many descriptions of prey capture by Dionaea muscipula (Venus flytrap) in popular publi-
cations and educational literature are inaccurate. Here we review well documented literature on prey
capture in this plant’s natural habitat and add observations on prey capture and attraction mecha-
nisms we have observed in plants cultivated in a greenhouse and garden.
Despite its common name “Venus flytrap” does not specialize in capturing flies. About 70% of
the prey it captures in its native habitat consists of spiders, ants, and beetles. Flies are only one-
to-eighteen percent of what it captures. In a greenhouse where flies, capable of entering the vents,
composed most of the available prey, over 90% of the prey captured were flies. Dionaea cultivated
in a garden captured a diverse array of animals, only about 37% of which were flies. Dionaea is a
generalist, capturing a wide variety of prey species. Its capture mechanism does not appear to have
a “syndrome” analogous to the Pollination Syndrome in flowers where a specific floral type is pol-
linated by a specific animal (i.e. Bee Flowers or Fly Flowers).
The measured capture rates of Dionaea are low, about one capture/leaf/month in its native habi-
tat. Similar but lower rates were measured in the greenhouse and garden. The single measurements
in each habitat need to be repeated, but the low rates are consistent with the observation that wher-
ever it is observed Dionaea has nearly all of its traps open. Both the low capture rates and the large
number of open traps suggests that alluring agents drawing prey either do not exist or are ineffective.
Despite reports of nectar secretion by Dionaea traps, our observations show that unstimulated traps
are always dry unless wet by rain, condensation, or a sprinkler system. Secretion occurs only after prey
capture. Alluring glands along the outer trap margin have been reported to be visited by small ants that
work their mouthparts over the glands. We have photographed a fly exhibiting the same behavior. The
exact nature of this behavior needs to be further investigated, but it does not appear that this attractant
can act at a distance since flies are as likely to land on the outside of a trap as on the inside.
Darwin proposed that the trap closure mechanism allows small prey to escape, preventing the ex-
penditure of energy on captures likely to be of little benefit. Recent measurements of prey captures
indicate that traps show little selectivity based on prey size and that while traps could, in theory,
select larger prey, statistically they do not behave this way.
Introduction
What prey does Dionaea muscipula capture?
Any carnivorous plant can only capture prey that is present in its environment. If placed in a
large terrarium with houseflies it can only capture houseflies. The prey present in the plant’s habitat

45Volume 46 June 2017
will determine what the plant’s traps can capture. However, other factors also determine what prey
will be found in traps. Some carnivorous plants have been reported to have extra floral nectaries,
attractive scents, and colors analogous to flowers. The relative attractiveness to prey would skew the
proportion of each type of prey animal captured. The mechanics of the trap such as the ability to
hold large prey, react quickly enough, etc. would also determine the type of prey captured.
It is the object of this paper to review the range of prey that is captured by Dionaea in various
habitats and determine if characteristics of the trap might favor the capture of specific types of prey.
Most early observations of prey capture were likely conducted on plants cultivated in greenhous-
es or gardens far away from the plants’ natural habitat and usually near human habitations. We will
call these the greenhouse habitat and the garden habitat. The first early common name for Dionaea,
“Catch Fly sensitive”, used in a 2 April 1759 letter to Peter Collinson from Gov. Arthur Dobbs of
North Carolina, infers that the plants primarily catch flies. Later Dobbs, in a 24 January 1760 letter
to Collinson, calls the plant “Fly Trap Sensitive” (Nelson 1990). Subsequent early references to Dio-
naea refer to it as “Tipitiwitchet” which has no reference to the prey captured, but when John Ellis
described the plant in the St. James Chronicle in 1-3 September 1773 he called it “Venus’s flytrap”
even though he knew that it captured many kinds of “little animals, such as Ear-wigs, Spiders and
Flies” (Nelson 1990). For its scientific name Ellis proposed “Dionaea Muscipula, which may be
construed into English, with humble submission both to Critics and foreign Commentators, either as
Venus’s Flytrap, or Venus’s Mousetrap.” The Latin species epithet muscipula actually means mouse-
trap, but the common name that took hold with the public was “Venus flytrap”.
The name Venus flytrap infers that the prey of Dionaea consists of flies, which in a greenhouse
with a population of flies, is what most of us who grow the plant observe. Most popular and educa-
tional descriptions of Dionaea also presume that flies are the major source of prey.
Methods
Prey capture measurements Natural Habitat (Lichtner & Williams 1978).
Leaves were collected in the f ield (Fig. 1 and Front Cover) from closed traps. For a thorough
discussion of Dionaea ecology, see Roberts and Oosting (1958). The prey animals were identified in
the field and preserved in alcohol. Specimens were reviewed in the laboratory to confirm the order
to which they belonged.
Greenhouse Habitat
Two large Dionaea plants with traps up to five cm, a selective breeding by Klaus Ivanez (Ger-
many), available in Germany and neighboring countries labeled with the additional designations
“Predator” and “Destroyer” (not registered as cultivars) were in 10×10 cm pots (Fig. 2). Entrance
of prey into the greenhouse was mostly restricted to the open vents, greatly favoring the entrance of
agile fliers such as flies. The two plants had about 25-33 active traps. The eight prey captured previ-
ous to our study in reopened leaves were photographed and identif ied. During the following 36 days,
13 additional prey animals were captured and identified after the traps reopened.
Garden Pond Habitat
A population of Dionaea plants similar to those found in the wild had been established in a large
pot with other carnivorous plants for about 20 years was used as the Garden Habitat. Access to prey
incapable of flight was limited because the pot was effectively an island in the garden pond (Fig. 3).
The population of plants had about 50 active leaves. The five prey captured previous to our study

46 Carnivorous Plant Newsletter
in reopened leaves were photographed and identif ied. During the following 80 days, 58 additional
prey animals were captured and identified after the traps reopened. In two captures, pairs of mating
mosquitos were captured together. These were each logged as a single capture.
Capture rate measurements Natural Habitat (Williams 1980)
Plants in the field near Supply, North Carolina, USA were marked by placing a numbered pot-
ting stake nearby. The leaf nearest the potting stake was leaf 1. The leaves were numbered clockwise
around the rosette notating the leaves that were closed (Fig. 1). Enough plants were staked to provide
data from about 224 leaves. The leaves were observed just after dawn, at noon, the evening, and the
following morning; closures of leaves were recorded. After the final observation the closed leaves
were opened to determine if capture of prey had occurred. The traps were then tested to see if they
were capable of rapid closure and 201 were. The number of closures with captures and closures
without captures were recorded and the number of captures in 24 hours was computed.
Greenhouse Habitat
The traps were photographed daily for 36 days during which there was an average of 29.2 active
traps. The observations were ended after 36 days because the weather had cooled enough that the
greenhouse vents did not open and insects were not able to easily enter. Monitoring during the next
Figure 1: Natural Habitat. Left: Zone between savannah and pocosin in the Green Swamp
in North Carolina. The Dionaea in the foreground are marked with stakes for capture rate
studies. Right: A close-up of one of the Dionaea plants.

47Volume 46 June 2017
two weeks showed no new captures were made when the vents were closed. Trap reopenings were
recorded instead of closures so capture rates were computed as reopenings/day.
Ultraviolet (UV) experiments
Measurements of UV reflection/absorption and fluorescence were made using an ultraviolet
lamp (Raytech Versalume UV-lamp with two glass filters for 254nm and 366nm) that emits a spec-
tral curve from approx. 230-420nm with two maxima at 254nm and 366nm. The emission spectrum
of the lamp has a visible shoulder from 380-420nm, which appears as dark-blue light. The invisible
long-waved UV radiation (around 366nm) is either reflected (impinging light spectrum = reflected
spectrum) or absorbed (no reflection, the surface remains dark) or it produces (with some excep-
Figure 2: Greenhouse Habitat. Above: The large Dionaea muscipula available in some
European countries with the additional designations “Predator” (left) and “Destroyer”
(not registered as cultivars) are on the bench in the foreground (white box). Competing
carnivorous plants capture more flies than the Dionaea. Below: A close-up of the Dionaea.

48 Carnivorous Plant Newsletter
tions, i.e. Rhodamine = red fluorescence at 580nm) a bright blue to cyan fluorescence between 420-
500nm (The impinging lamp spectrum becomes transferred into a bright visible light, shifted to a
longer wavelength by an optical active compound inside or upon the plant tissue). To evaluate such
UV studies requires some experience in order to differentiate between UV reflection and fluores-
cence and to avoid confusion and mistakes; in addition, safety glasses should be used. Dionaea and
the peristome of Nepenthes talangensis × truncata were observed for both UV reflection/absorption
and fluorescence. As reference for active fluorescence we used writing paper containing optical
Figure 3: Garden Pond Habitat. Above: Dionaea (white box) similar to that found in the
wild growing at the base of Sarracenia in the pot to the left rear. The pond is a barrier to
prey that cannot fly. Below: Close-up of the Dionaea.

49Volume 46 June 2017
brightener (Exact composition of the brightener was not labeled on the packaging, but usual for this
application is a stilbene derivate mixed with SiO2 as white f iller (also called white body)) that shines
super white1 under UV-radiation.
Review, new results, and discussion
Prey capture in the Natural Habitat
The first person to make an effort to actually see what Dionaea captures in its native habitat was
Charles Darwin (Darwin 1875, p 312-313). He wrote to Dr. Canby who “visited the native site of the
plant, early in the season, before the leaves had grown to their full size, and sent... [Darwin] fourteen
leaves, containing naturally captured insects. Four of these had caught rather small insects, viz. three
of them ants, and the fourth a rather small fly, but the other ten had all caught large insects, namely,
five elaters, two chrysomeles, a curculio, a thick and broad spider, and a scolopendra. Out of these
ten insects, no less than eight were beetles, and out of the whole fourteen there was only one, viz. a
dipterous insect, which could readily take flight.” This amounts to 1/14 flies, 3/14 ants, 1/14 spiders,
8/14 beetles, and 1/14 centipedes. Darwin notes that “only one of the 14 insects could readily take
flight but that Drosera ... lives chiefly on insects which are good flyers, especially Diptera, caught by
the aid of its viscid secretion”. Even at this early date there was strong evidence that Dionaea in its
native habitat captured a diverse array of insects, most of which could not readily take flight. Darwin
also stated in a footnote that Mrs. Treats’ cultivated-plants in New Jersey “chiefly caught Diptera”.
Dionaea in the garden habitat of Mrs. Treats captured flies while those in the wild or native habitat
captured an array of insects most of which could not readily take flight.
The next observation of prey captured by Dionaea in its native habitat was by Frank Morton
Jones (1923). Like Darwin, Jones observed a diverse array of insects captured. Jones sample of
50 prey animals, much larger than Darwin’s 14, shows 82% to be incapable of agile flight, close to
Darwin’s observation of 93%. A diverse group of beetles was captured just as Darwin observed but
a much smaller portion were beetles... 18% as opposed to Darwin’s 57%.
Two subsequent field studies have also been done on larger samples of prey captured by Dionaea
in its native-habitat. One based on captures by 152 traps (Lichtner & Williams 1977) and a second
based on captures by 337 traps (Hutchens & Luken 2009, 2015). A comparison of the results of all
four studies of captures by Dionaea in its native habitat is listed in Table 1. The percentage of flies
captured in the field varies from 1% (Hutchens & Luken 2009) and 18% (Jones 1923). The average
for all prey captured in the four studies is about 7% Diptera. The differences may be due to differ-
ences in the amount of carrion and fecal matter in the vicinity of the plants and thus the ability of
the habitat to generate flies.
The predominant prey animals captured in the natural habitat are spiders, ants, and beetles. Spiders
constitute approximately one third of the prey captured (18% Jones 1923, 30% Lichtner & Williams
1977, 31% Hutchens & Luken 2009, 2015). They have been reported resting in open traps (Lichtner &
Williams 1977) so it seems likely that they walk into the traps and take cover between the lobes. Ants
also constitute about one third of the prey (20% Jones 1923, 33% Lichtner & Williams 1977, 26%
Hutchens & Luken 2009). The ants must walk into the traps. Jones (1923) reports them being attracted
1 “Super White” sometimes also “superwhite” is an established term used for paper and laundry treated with an optical bright-
ener that generates a super white appearance due to a blue hue fluorescence usually at approximately 420nm under sunlight (or
any light containing UV). Such laundry detergents have been promoted for washing “whiter than white” or super white. The
term emerged in the 1960-70s and is still used in optical brightener-related chemistry as well as bright white paper and laundry
detergent promotion (Messier et al. 2005; https://en.alfakimya.com/textile-optical-brighteners).

50 Carnivorous Plant Newsletter
to the “alluring glands” along the edge of the trap. Beetles are the next most common prey captured
(18% Jones 1923, 12% Lichtner & Williams 1977, 12% Hutchens & Luken 2009, 2015). Various Or-
thoptera are also captured in significant numbers (14% Jones 1923, 14.5% Lichtner & Williams 1977,
2.4% Hutchens & Luken 2009). The remaining prey are diverse and captured in small numbers. Both
Jones (1923) and Lichtner and Williams (1977) used the older definition of Orthoptera that included
Blattodea so their capture numbers for Orthoptera are inflated by a few cockroaches.
Hutchens and Luken (2015) also identified the prey captured by Dionaea that were introduced
into habitat in South Carolina near already existing established populations. The captures made by
these introduced plants were very similar to those made by established plants native to the habitat
(Table 1).
It is clear from all the studies done in the natural habitat that flies are of minor importance as a
prey animal and that spiders, ants, and beetles are the bulk of the prey captured. Nearly all of the
prey animals captured in the natural habitat either are incapable of flight or are clumsy fliers.
Prey capture in the Garden and Greenhouse Habitats
For comparison we made limited observations of prey captured in the greenhouse habitat and
garden habitat (Table 2). In both of these habitats flies are a major component of the prey with the
garden habitat showing a lot more diversity.
Captures in the Garden Pond
Of the 50 active traps observed in the Garden Pond over 80 days there were 63 (65 prey) captures
37 or 59% Diptera. Thirty seven percent of the total captures were flies. Only two spiders and five
ants (four winged) were captured. No Orthoptera and only 2 (3.2%) Blattodea (cockroaches) were
captured. The Garden Pond is a 20-year-old stand of Dionaea in a large pot with other carnivorous
plants that effectively forms an island in a small garden pond. Because of this location flying insects
had more access to the traps than those incapable of flight. It is likely that a garden with better access
by flightless prey could see larger numbers of ants, spiders and other such flightless animals captured.
Table 1. Percentage of various orders of insects captured by Dionaea in its natural
habitat in the Carolinas.
Citation
Darwin Jones
Lichtner
&Williams
Hutchens &
Luken 2009
Hutchens &
Luken 2015
1875 1923 1977 Native Introduced
Arachnid (class) 7.1 18 29.6 31 22.5
Hymenoptera 21.4 20 32.9 28.3 42.8
Coleoptera 57.1 18 11.8 12.3 9.8
Orthoptera* 0 14 14.5 2.5 4.1
Diptera 7.1 18 4.6 1.5 3.5
Other 7.1 12 6.6 24.4 17.4
Total Captures 14 50 152 337** 227**
*Orthoptera used to include Blattodea. The earlier studies by Jones (1923) and Lichtner &
Williams (1977) include cockroaches in Orthoptera.
**Capture numbers provided by John J. Hutchens of Coastal Carolina University.

51Volume 46 June 2017
Captures in the Greenhouse
Of the 33 active traps in the greenhouse observed over 36 days there were 21 captures over 90%
of which were flies. One true bug and a bee were also captured. The strong impression, held by
many, that the main prey of Dionaea is flies is, no doubt, strengthened by similar observations by
those of us who grow this plant in our greenhouses.
The primary objective of Darwin (1875), Jones (1923), and Hutchens and Luken (2009) was to
test Darwin’s hypothesis that the structure and closure mechanism of Dionaea traps allow smaller
prey to escape so an emphasis was placed on the size of the prey captured rather than its type. The
analysis of the prey captured by Dionaea in its native habitat done by Lichtner and Williams (1976)
and Williams (1980) emphasized the type of prey captured. Looking at the data this way leads to
some important conclusions.
1. Dionaea captures a wide array of prey species.
The species captured are primarily determined by the species available in the habitat. There
does not seem to be a specific syndrome2 that defines the captures such as flying insects,
prey attracted to nectar, or prey that might be lured by a sex attractant. The capture mecha-
2 In flowers, a pollination syndrome is a suite of flower characteristics that result either in the attraction of specif ic animal pollen
vectors such as bees, hummingbirds, butterflies, or flies, often to the exclusion of other vectors, or characters that allow physical
vectors such as wind to be more effective. An example is the fly pollination syndrome, which has a smell that attracts flies and
often a trap that temporarily holds them (i.e. Amorphophallus species) while they pollinate the flower. Some flowers are general-
ists and have many pollinators (Faegri & van der Pijl 1979).
Table 2. Orders of insects captured by Dionaea in a garden habitat and a greenhouse
habitat.
Habitat GP Habitat GH Order
GP= Garden Pond captures,
GH= Greenhouse captures
39 19 Diptera GP (24 flies, 6 mosquitos*, 4 midges,
4 hoverflies, 1 fruit fly), GH (19 flies)
12 1 Hymenoptera GP (1 ant worker, 4 winged ants, 5 wasps,
1 bee, 1 unknown hymenoptera); GH (1 bee)
3 1 Hemiptera GP (2 cicadas, 1 green shield bug);
GH (1 green shield bug)
2 Blattodea GP (2 cockroaches)
2 Arachnida (class) GP (2 spiders)
2 Neuroptera GP (2 adult antlions)
1 Coleoptera GP (1 beetle)
1 Gastropoda (class) GP (1 snail)
1 Unknown GP (1 larva**)
3 Unknown GP (3 unidentifiable fragments)
66 21 Total
*Two times two mating mosquitos were captured together -- 8 mosquitos in 6 captures.
**The larva was likely brought into the trap by an ant that escaped.

52 Carnivorous Plant Newsletter
nism of Dionaea is not specific for flies. It is likely that most of the prey captured in its na-
tive habitat walks up the leaf petiole into the trap. The common name “flytrap” is mislead-
ing. In the various studies only between 1.5% (Hutchens & Luken 2009, 2015) and 18%
(Jones 1923) of the captured prey are Diptera while the rest are either non-fliers or clumsy
fliers. The presence or absence of animal carcasses or droppings nearby probably causes
the fly populations to fluctuate greatly but, in general, where Dionaea is native, relatively
few flies are captured. By contrast in the human related garden habitat and greenhouse
habitat many flies are captured.
2. Dionaea is a generalist in terms of the prey captured.
This brings into question suggestions of elaborate systems analogous with pollinator attrac-
tants in flowers such as alluring glands that act as nectaries (Jones 1923), UV patterns (Joel
et al. 1985), and attractive scents (Kreuzwieser et al. 2014). The descriptions of captures by
the “flytrap” and many of the proposed attractants may have been influenced by observa-
tions of Dionaea capturing flies in its greenhouse and garden habitats and by analogies with
fly pollinated flowers as opposed to looking at the plant in its native habitat where the evo-
lutionary pressures that led to development of its capture mechanism exist. Of the proposed
methods of attraction only Jones’ (1923) observation that ants are attracted to “alluring
glands” (Fig. 4) is documented.
While studying plants in the greenhouse habitat, a fly was observed moving to various points
on a trap working its mouthparts over the area with alluring glands in the same way that the small
ants described by Jones (1923) did (Fig. 4). This fly may have been attracted to the same thing that
Jones’ ants were but the attraction does not seem to act over longer distances since flies enter traps
only infrequently. A BBC ONE video (2009) shows a fly lapping abundant nectar from the area of
the alluring glands of a Dionaea trap. Our trap was dry (Figs. 4 & 5) and Jones (1923) does not
mention abundant secretion in the area where the ants he observed were attracted. In our experience
unstimulated traps that have not been wet by an outside source are always dry unlike those in the
WildFilmHistory (1974) and the BBC ONE video (2009).
Prey capture rates in various habitats
If Dionaea plants are observed in almost any setting, the majority of the traps are open, often
untouched by prey. This suggests that prey is captured infrequently. Captures and leaf closures with-
out capture by 201 functional Dionaea traps in the field were measured during 24 hours in its native
habitat by Lichtner and Williams (published in Williams 1980, see Table 3). Only six prey were
captured by the ten traps that closed during this period. At this rate about 0.9 prey captures would
occur per month so a plant with 6 functional traps would capture an average of approximately 5.5
prey a month. Capture rates may vary from day to day and according to conditions, but unless a large
source of prey becomes available or adverse weather occurs, we would expect this measurement is
in the normal range. This single observation should be supplemented by many more f ield measure-
ments of capture rates in order to be considered representative, but a low rate like this is what would
be expected if most the traps in the field are open.
An example of weather conditions affecting prey captures occurred on a day when it rained
continuously (Table 3). No captures were made. Interestingly 15 traps of 202 that were capable
of closing were closed without capturing prey as opposed to the 4 that closed on a day with no
rain. Raindrops striking the trigger hairs could have closed these. Those of us who have watered
Dionaea plants in a greenhouse probably agree that Darwin’s observation that “Drops of water or

53Volume 46 June 2017
a thin broken stream, falling from a height on the filaments did not cause the blades to close” is
usually accurate, although we have seen traps close on occasion when we watered them. However,
his statement that “no doubt as in the case of Drosera, the plant is indifferent to the heaviest shower
of rain” seems unlikely since a day of intermittently heavy showers resulted in 15 closures of 202
traps exposed to rain but probably not to prey animals while only 4 were closed on a clear day with
exposure to prey animals.
Figure 4: Close-up of a Dionaea trap. A= Alluring glands (green). S= Smooth area where
the trap seals when digesting prey. D= Digestive glands that secrete fluid and digestive
enzymes after prey is captured. T= Trigger hair, the sensory organ that triggers closure of
the trap. The fly has its mouthparts on the alluring glands that are dry.

54 Carnivorous Plant Newsletter
Captures in the Greenhouse and Garden Habitats
The capture rates computed for the Greenhouse and Garden Pond Habitats are listed in Table 4.
Though lower than capture rates in the natural habitat they were of the same magnitude. The Green-
house capture rates are lowest, about 34% of that of Dionaea in its natural habitat. This is likely part-
ly because access to the greenhouse by insects was limited during periods of cooler temperatures
when the greenhouse vents were closed. During two weeks of observations of greenhouse Dionaea
after the vents were closed no captures occurred so when the vents were closed the capture rate was
zero. The few flies that were able to enter when the vents were closed were captured by large Ne-
penthes, Sarracenia, and Drosera. These other carnivorous plants located near the Dionaea reduced
the prey available to the Greenhouse Dionaea (Fig. 2) at all times and contributed to the low capture
Figure 5: A single observation of a fly landing on a large Dionaea trap in the greenhouse.
It moved about the periphery of the leaf working its mouthparts on the area where the
alluring glands are located in a manner similar to the small ants observed by Jones
(1923). The trap is dry with no obvious nectar visible. This fly landed on the petiole and
walked into the trap.

55Volume 46 June 2017
rate. The Garden Pond Dionaea population captured prey at about 61% of the rate of Dionaea in its
natural habitat. It is likely that the pond water acted as a barrier to prey incapable of flight with only
reduced access over the lily pads on the water (see Fig. 3) thus reducing the number of captures.
Unfortunately it is impossible to make firm conclusions based on single samples of the capture rate
in each location. An additional problem in comparing the capture in the Greenhouse with those in
the Garden Pond arises because the plant forms of Dionaea are different. In the greenhouse, the
locally-named “Predator” and “Destroyer” plants had large traps ranging up to 5 cm in size, while
the plant in the Garden Pond was the common form of Dionaea muscipula similar to those found in
the wild. More extensive sampling under better-controlled conditions needs to be done. In addition,
in the future, controlled experiments on the comparative attractiveness of various carnivorous plants
to different types of prey should be made. Also other carnivorous plants in the greenhouse were in
competition with Dionaea for the flies. The competing Nepenthes species attracted prey with abun-
dant nectar drops and Drosera fragrans and Drosera aff. indica “Africa” have a noticeable fragrance
produced by their leaves, both of these attractants are lacking in the Dionaea we observed.
Alluring prey to traps
Numerous flowers have various mechanisms that attract pollinators (Faegri & van der Pijl 1979).
There is strong evidence that some carnivorous plants have similar mechanisms that attract prey
(Jürgens et al. 2009; Moran & Clark 2010). Such attraction or alluring mechanisms have been pro-
posed to exist in Dionaea, but much of the information is from secondary sources without citations
or from selected poses from educational videos, such as the BBC ONE video (2009). Many state-
ments about such mechanisms have been made with little evidence to support them. Those that seem
reasonable are often accepted as accurate and get widely repeated in popular literature and educa-
tional material on Dionaea. Some of the alluring mechanisms may even exist, but far more rigorous
observation and experimentation should occur before we accept descriptions of them as accurate.
The following alluring mechanisms have been proposed to exist in Dionaea:
1. Alluring glands, a name assigned to glands structurally identical to digestive glands, were
named by Jones (1923). They are located just beyond the smooth area around the edge of
the trap inside the “cilia” along its rim (Fig. 4). These are not pigmented like most digestive
glands and are slightly smaller in size. Jones (1923) reported that in its native-habitat small
ants were attracted to these glands and that they move their mouthparts over them as if taking
Table 3. Prey capture in 24 hrs. by Dionaea in
its native habitat during periods of heavy rain
and no rain.*
Weather Rain No Rain
Total Traps 244 224
Traps that could close** 202 201
Captures 0 6
Closures without capture 15 4
*The study was done in late June near Supply, NC.
**Measured by triggering open traps after
observations.
Table 4. A comparison of capture
rates in different habitats.
Habitat Captures/leaf/month
Garden Pond 0.55
Greenhouse 0.30
Natural 0.89

56 Carnivorous Plant Newsletter
up nectar. He also reported that a large wasp exhibited the same behavior. There are numerous
undocumented secondary sources that state that nectar is secreted by these glands and pos-
sibly a scent. There are also impressive educational videos of flies attracted to these glands.
We have never seen secretion from these glands and other than Jones’ paper, there is little
scientific work to indicate that they act as nectaries. When we observed the glands under the
microscope, no secretion was visible. Except when wet by external sources, such as misting
systems, the glands in unstimulated traps were always dry. The dry traps of Dionaea are prob-
ably an advantage since it makes most captures in hot and sunny weather. By comparison, in
such weather the nectar secreted by Nepenthes pitchers becomes very viscous, finally crystal-
lizing (Fig. 6). In Dionaea such incrustations would prevent smooth sealing when the traps
close and complicate digestion by drying out the trap contents.
2. Alluring scents have been proposed. Jürgens et al. (2009) studied volatiles emitted from
the traps of a number of carnivorous plants. In three species of Sarracenia, compounds
typically found in flowers or fruits were found, suggesting that together with other fea-
tures such as color and nectar production, the emitted volatiles may allow the traps to act
as flower or fruit mimics. However, they found that the leaves of S. purpurea, Dionaea
muscipula, and Drosera binata emitted much weaker scents with lower numbers of com-
ponents, consisting mainly of volatiles typically emitted from green leaves. This does
not support the notion of a scent acting as a part of a suite of attractants in Dionaea.
In a more recent study, Kreuzwieser et al. (2014) found that Dionaea releases volatile or-
ganic compounds including terpenes, benzenoids, and aliphatics that attract fruit flies (Dro-
sophila melanogaster). They concluded that Dionaea attracts insects using food smell mim-
icry “since the scent released has strong similarity to the bouquet of fruits and plant flowers”.
This does not sound like the “weaker scents with lower numbers of components, consisting
mainly of volatiles typically emitted from green leaves” described by Jürgens et al. (2009).
In addition, fruit flies are not typical prey of Dionaea. Only one fruit fly was captured dur-
ing our observations. Would spiders, grasshoppers, and many of the range of prey in Dionaea
traps be attracted by floral or fruity scents? This seems unlikely.
3. Red coloration mimicking meat such as fly pollinated flowers has been said to attract flies.
Carrion flowers actually do attract fly pollinators in this way and some, such as skunk cab-
bage (Symplocarpus foetidus) and Aristolochia have a red color resembling carrion in addi-
tion to the appropriate scent (Faegri & van der Pijl 1979). Red coloration of pitcher plants has
been reported to attract prey (Schaefer & Ruxton 2008), but more recent experiments show
that nectar rather than color is the attractant (Bennett & Ellison 2009). There is evidence that
the red coloration of Drosera is not involved in prey attraction (Foot et al. 2014; Schaefer
& Ruxton 2008). In Dionaea there is no evidence that the red coloration of the traps are in-
volved in prey capture. The presence of both red and green traps in the wild and the lack of
red color’s involvement in other carnivorous plants makes it unlikely that Dionaea traps red
coloration plays an important role in attracting prey. Dionaea traps lack the potent carrion
smell or fecal smell often present in fly pollinated flowers and is not likely to be a carrion
mimic.
4. Ultraviolet (UV) patterns similar to those that attract flower pollinators have been described
by Joel et al. (1985). Included in their account is a photograph and description of the UV
pattern on a Dionaea trap. It shows the zone of the trap with the alluring glands absorbs ultra-
violet light and the zone with digestive glands reflects it. A pattern would therefore be visible
to insects with UV vision, such as bees. They state that this is evidence in favor of Jones’

57Volume 46 June 2017
(1923) idea of a baited system over Lichtner and Williams (1977) proposal that traps are not
baited and prey capture is non-specific. Our observations with a 230-420nm UV-lamp with
peaks at 254nm and 366nm show a pattern that results from a difference in reflection of UV
by the inner digestive zone and absorption on the upper margin of the trap zone with alluring
glands (Figs. 4 & 7). While this pattern agrees with the data of Joel et al. (1985), compared
with the patterns of flowers that are known to attract insects, this pattern lacks contrast and
is unspectacular. In addition, we found no visible fluorescence from Dionaea traps similar
to that observed from traps of other carnivorous plants such as peristomes of Nepenthes and
Figure 6: A = The trap of Nepenthes bicalcarata with attracting nectar drops on the
outside. B = During the hot season the secreted nectar becomes very viscous and forms
incrustations of crystallizing sugar. C = The open trap of Dionaea is always dry, smooth
and shiny.

58 Carnivorous Plant Newsletter
Sarracenia (Fig. 7, Kurup et al. 2013; Hartmeyer et al. 2013). This lack of active fluores-
cence and the rather inconspicuous pattern due to reflection and absorption suggests that UV
is not involved in attracting prey.
Does the size of prey matter?
Darwin (1875) noticed that when an insect enters a Dionaea trap and touches a trigger hair twice
or two trigger hairs once, the trap rapidly closes such that the marginal projections (“cilia”) on each
of the opposing lobes bar the escape of larger prey. Struggles against the trigger hairs cause the trap
to completely close, sealing the lobes along the smooth areas on the surface of the trap near its rim.
Figure 7: A = Dionaea under UV showing no luminescence. B = Dionaea under UV with
a piece of super white paper (containing fluorescent optical brightener) as reference.
The very bright luminescence of the super white paper as reference proves that enough
UV-light is given to excite fluorescence when present. C = The dark blue light (approx.
380-420nm) that is emitted by the UV-lamp is reflected from the digestive zone together
with invisible UV (maximum at 366nm). The margin with alluring glands shows very low to
no reflection. This confirms a UV-pattern as shown by Joel et al. (1985). But it is not very
spectacular compared with the patterns of attractive flowers. D = The peristome of this
Nepenthes talangensis × truncata shows a bright and clear fluorescence under UV. The
UV from the lamp (366nm) is transferred into bright visible light, which is shifted to the
longer wavelength at approx. 490nm (blue-cyan).

59Volume 46 June 2017
Smaller insects should be able to escape during the period that the trap is partially closed. Darwin
said one of his sons actually observed this. He thought allowing the small prey to escape would save
the plant a great deal of energy expenditure on a capture that was of little value to the plant. Dar-
win’s letters to Canby and his request for captured insects were explicitly done to test this hypoth-
esis (Jones 1923). Of the 14 insects captured, 3 were small and 11 were large enough to have been
retained by the marginal projections blocking their way. He considered this adequate evidence for
his model despite 21% of the captures in the small sample being of a size that should have escaped.
However, Jones (1923) did not accept the model on this basis. Jones looked at captures by 50 traps
and found of the 50 captures only one was less than 5 mm in length and only 7 were less than 6 mm.
Ten were 10 mm or more in length with a maximum of 30 mm. Jones (1923) concludes that in the
mature traps he studied, prey less than 1/4 in (= 6.35 mm) escape while others are captured. Sixteen
percent of his larger sample was small enough to have escaped compared to 21% of Darwin’s. Jones
accepted Darwin’s model presuming that most of the smaller prey had escaped.
A more elaborate experiment was done by Hutchens and Luken (2009) with a much larger sam-
ple of 337 captured prey. They compared leaf size with capture size in large, medium, and small
sized traps. With the exception of a few infrequently captured large prey animals captured by large
traps, all three sizes of traps captured the same range of sizes of animals. Large, medium, and small
traps all tend to catch relatively small prey. Larger traps can let small prey escape, but it does not ap-
pear that they are very good at the task of primarily collecting large prey. Hutchens and Luken’s data
does show that the larger size traps collect larger prey on average due to a few very large captures,
so a larger trap is better able to capture larger animals than the smaller traps. However, it is not clear
if this advantage is due to letting small ones escape or just being able to hold onto a larger prey item
compared to a smaller trap. They conclude that “Carnivory in Dionaea is not size selective” and that
“Large insects were not preferentially captured”. Perhaps Darwin’s elegant idea about the efficiency
of letting the “small ones get away” may occur but may not be the general case.
How is prey captured by Dionaea traps?
The answer depends on where the observation is made. A Dionaea plant in a greenhouse will
likely have a fly land directly on its leaf. The fly in Figure 4 landed on the petiole of the trap and
walked into it. The prey then moves around in the trap, possibly visiting the area of the alluring
glands. If it brushes the trigger hairs twice the trap will snap shut. Its struggles will lead to trap nar-
rowing and the digestion of the prey. After digestion, the trap will reopen and only the exoskeleton
of the fly will remain. This scenario is well illustrated by Attenborough (1995) in a video that shows
a beetle walking up a trap growing wild in the Carolinas into the trap that is then triggered and closes
and digests the insect as described above.
A Dionaea plant growing wild in the sandy soils of the coastal regions of the Carolinas in the
open sun with pine trees nearby is likely to have an ant or beetle walk up its petiole into the trap or
to have a spider select it as a hiding place. If any of these animals stimulates two trigger hairs (or
one hair twice) the trap will close on it, the struggle of the prey will cause narrowing, and the prey
will be digested except for the exoskeleton which will remain after the leaf opens.
It is possible that ants are lured into the trap (Jones 1923), or that they just blunder in, as the
beetles certainly must. The spiders appear to be attracted to the traps as a hiding place (Williams
1980). Other than Jones’ observation, there is no evidence of alluring prey into Dionaea traps except
in the popular and educational literature and videos. There may be lures of some type but convincing
evidence is lacking.

60 Carnivorous Plant Newsletter
Both in the greenhouse and the wild, the trap will remain partly open for a while with the way
out barred by the marginal spikes (cilia) along the edge of the leaf. During this period small prey
can escape from large traps but according to Hutchens and Luken (2009), statistically most do
not.
The Venus flytrap is the first thought to come to most people’s mind when someone says “car-
nivorous plant”. It is unfortunate that we do not have better information on the interaction with the
prey captured by the plant in its native-habitat. Descriptions and even careful experiments based on
this plant’s behavior in greenhouses and gardens far away from its native habitat have led to a great
deal of lore about its behavior right down to the notion that it is primarily a fly-catching plant. Once
established, this lore takes on a life of its own. Not all of it is necessarily false, but far more rigorous
observations with reference to the plant in its native habitat needs to be done before we accept it as
fact. We have to ask, should Dionaea muscipula even be called a flytrap?
Acknowledgements: The authors thank John Hutchens of Coastal Carolina University for provid-
ing information on the numbers of captures made in his studies and for reviewing the parts of the
manuscript that covered his work. We also thank Irmgard Hartmeyer for her support of the garden
and greenhouse observations as well as her helpful comments on our paper. Further thanks go to
both peer-reviewers who helped to improve the article.
References
Attenborough, D. 1994. The Private Life of Plants, a BBC Nature Documentary series. https://www.
youtube.com/watch?v=ktIGVtKdgwo
BBC One. 2009. Life: Venus Flytraps: Jaws of Death, narrated by David Attenborough. https://
www.youtube.com/watch?v=O7eQKSf0LmY
Bennett, K.T., and Ellison, A.M. 2009. Nectar, not colour, may lure insects to their death. Biology
Letters 5(4): 469-472.
Darwin, C. 1875. Insectivorous Plants. John Murray, London. 462p.
Faegri, K., and van der Pijl, L. 1979. The Principles of Pollination Ecology. Pergamon, Oxford.
244p.
Foot, G., Rice, S.P., and Millett, J. 2014. Red trap colour of the carnivorous plant Drosera rotundifo-
lia does not serve a prey attraction or camouflage function. Biology Letters 10 20131024; DOI:
10.1098/rsbl.2013.1024.
Hartmeyer, S.R.H., Bayerl, R., and Hartmeyer, I. 2013. Leuchtende Karnivoren: Die Lumineszenz
der Schierlingsbecher. Das Taublatt 75: 33-44.
Hutchens, J.J., and Luken, J.O. 2009. Prey capture success by established and introduced popula-
tions of the Venus Flytrap (Dionaea muscipula). Ecological Restoration 33(2): 171-177.
Hutchens, J.J., and Luken, J.O. 2015. Prey capture in the Venus flytrap: collection or selection?
Botany 87: 1007-1010.
Joel, D.M., Juniper, B.E., and Dafni, A. 1985. Ultraviolet patterns in the traps of carnivorous plants.
New Phytologist 101(4): 585-593.
Jones, F.M. 1923. The most wonderful plant in the world. Natural History 23(6): 589-596.
Jürgens, A., El-Sayed, A.M., and Suckling, D.M. 2009. Do carnivorous plants use volatiles for at-
tracting prey insects? Functional Ecology 23: 875-887.
Kreuzwieser, J., Scheerer, U., Kruse, J., Burzlaff, T., Honsel, A., Alfarraj, S., Georgiev, P., Schnitzler,
J.P., Ghirardo, A., Kreuzer, I., Hedrich, R., and Rennenberg, H. 2014. The Venus flytrap attracts

61Volume 46 June 2017
insects by the release of volatile organic compounds. Journal of Experimental Botany 65(2):
755-766.
Kurup, R., Johnson, A.J., Sankar, S., Hussain, A.A., Kumar, C.S., and Sabulal, B. 2013. Fluorescent
prey traps in carnivorous plants. Plant Biology 15(3): 611-615.
Lichtner, F.T., and Williams, S.E. 1977. Prey capture and factors controlling trap narrowing in Dio-
naea (Droseraceae). American Journal of Botany 64(7): 881-886.
Messier, P., Baas, V., Taf ilowski, L., and Varga, L. 2005. Optical brightening agents in photographic
paper. Journal of the American Institute for Conservation 44(1): 1-12.
Nelson, E.C. 1990. Aphrodite’s Mousetrap: a biography of Venus’s flytrap, with facsimiles of an
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145p.
Roberts, P.R., and Oosting, H.J. 1958. Responses of Venus fly trap (Dionaea muscipula) to factors
involved in its endemism. Ecol. Monographs 28: 193-218.
Schaefer, H.M., and Ruxton, G.D. 2008. Fatal attraction: carnivorous plants roll out the red carpet
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wildfilmhistory.org/film/330/clip/815/Carnivorous+plants+-+capture+and+devour.html
Williams, S.E. 1980. How Venus’ flytraps catch spiders and ants. Carnivorous Plant Newsletter 9(3):
65,75-78.

CARNIVOROUS PLANT
NEWSLETTER
Journal of the International Carnivorous Plant Society
Volume 46, No. 2 June 2017

Carnivorous Plant Newsletter42
Front Cover: Upper half: Dionaea habitat in the zone between a pocosin and longleaf pine savannah in the
Green Swamp, Brunswick County, North Carolina in 1974. The young man in the photograph is Frank Lichtner
studying the prey captured by Dionaea. Lower right: Another Dionaea habitat area, overgrown by grass that will
eventually shade out the Dionaea if there is no fire. Lower left: A Dionaea plant in the Green Swamp (Cover of
Science 1218(4577)10/12/1982. Reprinted with permission from AAAS). Article on page 44.
Back Cover: A three-year-old juvenile specimen of Roridula gorgonias in cultivation. Photo by Barry Rice.
Article on page 74.
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