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Efficiency of antlion trap construction

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Assessing the architectural optimality of animal constructions is in most cases extremely difficult, but is feasible for antlion larvae, which dig simple pits in sand to catch ants. Slope angle, conicity and the distance between the head and the trap bottom, known as off-centring, were measured using a precise scanning device. Complete attack sequences in the same pits were then quantified, with predation cost related to the number of behavioural items before capture. Off-centring leads to a loss of architectural efficiency that is compensated by complex attack behaviour. Off-centring happened in half of the cases and corresponded to post-construction movements. In the absence of off-centring, the trap is perfectly conical and the angle is significantly smaller than the crater angle, a physical constant of sand that defines the steepest possible slope. Antlions produce efficient traps, with slopes steep enough to guide preys to their mouths without any attack, and shallow enough to avoid the likelihood of avalanches typical of crater angles. The reasons for the paucity of simplest and most efficient traps such as theses in the animal kingdom are discussed.
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3510
Introduction
The use of traps for predation has evolved independently in
several groups of animals (e.g. spiders, wormlion larvae,
trichopteran larvae) (Alcock, 1972). This strategy reduces the
amount of energy expended in hunting and chasing prey, but
the construction of the trap is itself energy- and time-
consuming. Spiders are the main group of trap-building
animals, with over 10·000 species (Foelix, 1996). Despite
considerable variation of web architecture, and the stunning
beauty of some webs, very few studies have investigated the
costs and benefits of web architecture (Opell, 1998; Craig,
1987; Craig, 1989; Herberstein and Heiling, 1998). The most
recent comprehensive study, based on the large energy budget
of the Zygiella x-notata spider, showed that a small increase in
web size translates into a large increase in prey biomass, due
to an increase in the likelihood of catching large and heavy prey
(Venner and Casas, 2005). Thus, spiders clearly adapt their
traps as a function of costs and benefits. The geometric
complexity of spider webs, differences in material and
structural properties and the re-ingestion of webs by many
spiders make it difficult to study the optimality of construction
of these structures. The geometric simplicity of the antlion
(Myrmeleontidae) trap makes this model more accessible than
spiders’ webs for studies of the relationship between predation
and the structure of the trap – the object of this study.
Several antlion species live in sandy habitats and their larvae
dig funnel-shaped pits to catch small arthropods, primarily ants.
The pits are dug starting from a circular groove, the antlion
throwing sand with its mandibles. Afterwards, the antlion
gradually moves down in a spiral from the circumference
towards the centre, making the pit deeper and deeper
(Tuculescu et al., 1987; Youthed and Moran, 1969). At the end
of construction, the antlion is generally located at the trap
centre. It may move away from the centre over time (personal
observations). The antlion trap functions by conveying the prey
towards the base of the trap (Lucas, 1982). When the prey
arrives at the bottom of the pit, the antlion rapidly closes its
mandibles. If the prey is not bitten at the first attempt and tries
to climb up the walls of the trap, the antlion violently throws
sand over it to destabilise it and attempts to bite it (Napolitano,
1998).
The costs inherent in trap-based predation can be minimised
by choices concerning: (1) the location of the trap, (2) the
‘giving up time’, defined as the time for which the predator is
prepared to wait before changing location and (3) the structure
of the trap (Hansell, 2005). The location of the trap is
determined on the basis of a number of criteria, including prey
density (Griffiths, 1980; Sharf and Ovadia, 2006), soil granule
size distribution (Lucas, 1982), the density of other animals of
the same genus (Matsura and Takano, 1989) and disturbance
Assessing the architectural optimality of animal
constructions is in most cases extremely difficult, but is
feasible for antlion larvae, which dig simple pits in sand to
catch ants. Slope angle, conicity and the distance between
the head and the trap bottom, known as off-centring, were
measured using a precise scanning device. Complete attack
sequences in the same pits were then quantified, with
predation cost related to the number of behavioural items
before capture. Off-centring leads to a loss of architectural
efficiency that is compensated by complex attack
behaviour. Off-centring happened in half of the cases and
corresponded to post-construction movements. In the
absence of off-centring, the trap is perfectly conical and
the angle is significantly smaller than the crater angle, a
physical constant of sand that defines the steepest possible
slope. Antlions produce efficient traps, with slopes steep
enough to guide preys to their mouths without any attack,
and shallow enough to avoid the likelihood of avalanches
typical of crater angles. The reasons for the paucity of
simplest and most efficient traps such as theses in the
animal kingdom are discussed.
Supplementary material available online at
http://jeb.biologists.org/cgi/content/full/209/18/3510/DC1
Key words: animal construction, antlion pit, sit-and-wait predation,
physics of sand, psammophily.
Summary
The Journal of Experimental Biology 209, 3510-3515
Published by The Company of Biologists 2006
doi:10.1242/jeb.02401
Efficiency of antlion trap construction
Arnold Fertin* and Jérôme Casas
Université de Tours, IRBI UMR CNRS 6035, Parc Grandmont, 37200 Tours, France
*Author for correspondence (e-mail: arnold.fertin@etu.univ-tours.fr)
Accepted 21 June 2006
THE JOURNAL OF EXPERIMENTAL BIOLOGY
3511Antlion trap construction
(Gotelli, 1993). In some species, the giving up time is
determined as a function of the frequency of prey captured
(Heinrich and Heinrich, 1984; Matsura and Murao, 1994).
Antlions are also able to adapt the design of their trap (e.g. the
diameter/height ratio) in response to variations in prey
availability (Lomáscolo and Farji-Brener, 2001). The direct
impact of the geometric design of the trap on the efficacy of
predation at a given constant prey density remains unknown.
This animal-built structure is constrained by the physical
properties of the soil, in particular the crater angle, which is a
physical constant of the sand that defines the steepest possible
slope not leading to an avalanche (Brown and Richards, 1970).
This angle should be distinguished from the talus angle, which
is valid for a heap of sand. The crater angle is greater than the
talus angle because it involves arch and buttress phenomena
(Duran, 2000).
Attack behaviour (i.e. behaviour such as sand throwing and
bite attempts) when the prey attempts to escape involves an
energy cost for the antlion with respect to the situation in which
the prey is conveyed immediately to the base of the trap and
immobilised with the first bite. Cost of predation is minimal
when there is no attack behaviour. Trap slope modifies prey
movements: the weaker is the slope, the easier the locomotion
is (Botz et al., 2003). We can thus expect a decrease of
predation cost with trap angle (Fig.·1). The aims of this study
were to define the efficiency of trap geometry in terms of attack
behaviour.
Materials and methods
Three-dimensional analysis
We calculated the three-dimensional (3D) surface of the trap
by measuring all three dimensions with a scanner system
developed in the laboratory and inspired by the work of
Bourguet and Perona (Bourguet and Perona, 1998). This
system functions by projecting the shadow of a plane on the
surface of the trap (Fig.·2A) (see supplementary material for
the calculus details). A camera (Euromex VC3031) records the
deformation of the shadow. The data were extracted as pixel
co-ordinates in ImageJ (Abramoff et al., 2004) and were then
processed digitally in the R environment. The surface of the
trap was reconstructed by linear interpolation of the scattered
points on a grid (with each square on the grid being
0.5·mm0.5·mm) (Akima, 1996) (Fig.·2B). Various geometric
parameters were calculated from this surface (Fig.·2C). The
centre of the trap was identified as the lowest point of the
surface, corresponding to the point at which all objects falling
into the trap should arrive. The height of the trap is the
difference in height between the centre and the mean height of
the points on the rim of the trap. The data were subjected to
least mean square adjustment on the conical surface given by
the equation:
(x O
x
)
2
+ (y O
y
)
2
– (z O
z
)
2
tan
2
[(/2) – ] = 0·, (1)
The parameter is the mean angle with respect to the
horizontal of the walls of the trap. The estimated points
(O
x
,O
y
,O
z
) correspond to the summit of the inversed conical
surface. The diameter was determined from the adjusted
surface, at the mean height of the points of the rim of the trap.
The goodness-of-fit of the data was assessed by determining
the root mean square error (RMSE):
RMSE = RSS/n·, (2)
where RSS is the squared sum of the residuals and n is the
number of points on the surface of the trap. RMSE gives a mean
difference in mm of the deviation from the adjusted conical
model. As an example, a RMSE of 0.4·mm corresponds to a
mean lack of conicity by about two grains of sand. The 3D co-
ordinates of the head of the antlion (corresponding to the
median point between the eyes) were calculated from the pixel
co-ordinates on the image and by projection on the surface. The
distance separating the head from the centre is referred to as
off-centring (Fig.·2C).
Behavioural experiments
Stage 2 and 3 larvae of Euroleon nostra Fourcroy
(Neuroptera, Myrmeleontidae) were collected at Tours
(47°2116.36N, 0°4216.08E, France) and raised in the
laboratory for six months with constant nutrition provided.
Larval stage was determined by measuring the width of the
cephalic capsule (Friheden, 1973). Lasius fuliginosus Latreille
(Hymenoptera, Formicidae) workers were used as prey in
observations of predation behaviour, as carcasses of this
species were frequently observed around traps in the field. The
antlions were provided with sand of known particle size
distribution (Fontainebleau sand SDS190027, particles of 100
to 300·m in size). The antlions were placed in square Perspex
boxes (11116·cm) 16·h before the experiment. The traps
constructed were thus studied the first time they were used. The
boxes containing the animals were placed on a base mounted
on ball bearings so that they could be correctly positioned for
filming without disturbance. All experiments were carried out
at the same time of day (between 10.00 and 10.30·hours), in
Angle
Predation cost
0
α
WO
α
WO
Physical limit of sand
Maximal
efficiency
Loss of
efficiency
Fig.·1. Hypothetical relationship between predation cost and trap
angle. The shaded part of the graph corresponds to angles greater than
crater angle (
c
), which cannot be achieved because of the physical
properties of sand.
WO
is the theoretical angle without off-centring.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
3512
conditions of controlled temperature (24.4±1.7°C) and
humidity (43.7±6.3%; mean ± standard deviation). We scanned
the pits dug by the antlions before introducing an ant into the
box, close to the trap. Predation sequences were filmed in their
entirety with the same camera used to record the scan. These
sequences were then analysed frame-by-frame (25·frames·s
–1
).
The recording of the sequence continued until the death of the
prey. Capture time was measured by counting the number of
frames between the moment at which the prey arrived at the
bottom of the trap and the moment at which the fatal bite was
delivered. This final bite was followed by a specific pattern of
behaviour, in which the ant was shaken and then buried in the
sand. The cost of prey capture was quantified by counting the
number of attempts to bite the prey or to throw sand over the
prey for each predation sequence. Each attack behaviour entails
a cost in terms of time and energy. To summarize, an
experiment followed this sequence: we first put an antlion in a
box of sand with known granular properties, it was allowed to
dig a trap and 3D modelling of the trap was undertaken; we
then put an ant in the box and analysed the attack behaviour
and trap geometry.
Measurement of crater angle
The measurement and definition of the drained angle of
repose can be achieved by three types of analysis, each of
which provides a slightly different angle: conical heap, two-
dimensional slope and crater angle (Brown and Richards,
1970). By analogy with the funnel-shaped trap of the antlion,
we chose to measure crater angle. This angle was measured on
A. Fertin and J. Casas
30 artificial cones obtained by filling a circular box (8·cm in
diameter, 2·cm high), in which a 1.19·mm hole had been made
in the base, with the same sand as was used in the experiments
described above. A crater is formed when the sand escapes
via the hole. The angle of the slope of this crater is the crater
angle. These cones were scanned and their surfaces were
reconstructed and adjusted, based on conical area, as described
above. Thus, for each artificial cone, we obtained a
measurement of crater angle and a measurement of deviation
from the model cone. The mean angle obtained,
c
,
corresponds to the value of the drained angle of repose by a
crater. The mean RMSE value obtained, RMSE
c
, corresponds
to the smallest deviation from the model cone, taking into
account the precision of the apparatus and the size of the grains
forming the surface. The values of crater angle and RMSE
measured on the traps dug by the antlions were compared with
c
and RMSE
c
as follows:
angle
=
c
and
RMSE
= RMSE – RMSE
c
.
Statistical analysis
We assessed the correlations between various geometric,
behavioural and predation variables, by calculating Pearson’s
correlation coefficients and carrying out Student’s t-tests. We
used linear models for the correlation between certain variables
for which the significance of the correlation was tested by
means of F-tests. The narrow range of angles measured allows
us to apply a linear model without transformation (Batschelet,
Fig.·2. Reconstruction and 3D
measurements of an antlion trap.
(A) Diagram of the set-up. The
light source projects a shadow of
the edge of the plane on the scene.
The edge of the plane and the
shadow are projected onto the
normalised image plane of the
camera, and the resulting image is
used to reconstruct the three-
dimensional scene in the camera’s
reference frame O(X,Y,Z). (B)
Reconstruction of the trap surface.
(C) Geometric variables measured
on the surface of the trap (green
line) and on the conical surface
(black line). The figured off-
centred position is exaggerated for
the purpose of illustration.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
3513Antlion trap construction
1981). The significance of differences of variables between
larval stage 2 and 3 was tested by means of Wilcoxon tests.
The significance of the parameters generated by these models
was assessed by means of Student’s t-tests. All means and
estimates are given with their 95% confidence interval (mean
± 95% confidence interval).
Results
Trap architecture
The values of RMSE are weak, from 0.18·mm to 0.71·mm,
indicating that traps are never far from a perfect conical model.
Out of 24 antlions, seven had an off-centring of less than 1·mm,
and 15 had an off-centring less than 2·mm. Thus, off-centring
is generally minimal, of the order of the size of its head.
Diameter, height, angle, RMSE and off-centring measured on
stage 2 larvae were not distinct from those measured on stage
3 larvae (respectively: W=40, P=0.720; W=54, P=0.3311;
W=84, P=0.494; W=43, P=0.1056; W=42, P=0.0933; N=24).
Angle was negatively correlated with RMSE (r=–0.7248,
t=–4.9350, P<0.001, N=24). Angle was also negatively
correlated with off-centring (r=–0.6481, t=–3.9917, P<0.001,
N=24). RMSE was positively correlated with off-centring
(r=0.7833, t=5.9112, P<0.001, N=24). Thus, the two geometric
parameters, trap angle and RMSE, vary similarly with off-
centring. As off-centring was observed in all cases, we also
investigated the values of trap angle and RMSE in the absence
of off-centring (
wo
and RMSE
wo
). A linear model accounting
for changes in
angle
as a function of off-centring (R
2
=0.42,
F=15.93, P<0.001, N=24) predicted that, in the absence of
off-centring,
angle
would be significantly different from
zero (intercept:
angle
=4.5279±1.2674°, t=7.409, P<0.001)
(Fig.·3A). The theoretical angle
wo
(37.0594±1.2674°) is
therefore significantly smaller than the crater angle
c
(41.6085±0.2366°; N=30). The study of the distribution of
angles measured on antlion constructions showed that the mode
was located in the confidence interval of
wo
(Fig.·4). Only one
trap had an angle greater than the upper limit of this confidence
interval. Similarly, linear regression (R
2
=0.6136, F=34.94,
P<0.001, N=24) was used to predict
RMSE
in the absence of
off-centring (Fig.·3B). The predicted
RMSE
in the absence of
off-centring did not differ significantly from zero (intercept:
RMSE
=0.0359±0.0533mm, t=1.396, P=0.177). The theoretical
RMSE, RMSE
wo
=0.2478±0.0533·mm, is therefore not
significantly different from the RMSE
c
of 0.2098±0.0130·mm
(N=30). In the absence of off-centring, the antlion is therefore
able to construct a perfectly conical trap with a slope shallower
than the maximal slope permitted by the physics of sand.
Impact of trap geometry on predation cost
All ants were captured during the experiments, ensuring a
finite capture time. Out of 24 antlions, seven displayed no
attack behaviour to catch their prey, and five used attack
behaviours consisting of only one sand throwing or bite
attempt. We did not observe avalanches triggered by ant
struggle. Capture time was positively correlated with the
number of times sand was thrown (r=0.9292, t=11.79,
P<0.001, N=24), and with the number of attempts to bite the
prey (r=0.7349, t=5.0824, P<0.001, N=24). Capture time was
a linear function of the number of times sand was thrown and
the number of attempts to bite the prey (R
2
=0.9329, F=145.9,
P<0.001, N=24). Capture time was therefore considered to
represent the cost of predation, as it is known that the number
of times sand is thrown has a strong effect on predation cost
(correlation between capture time and number of times sand
thrown: r=0.9292, t=11.7899, P<0.001, N=24; correlation
between capture time and number of biting attempts:
r=0.7348753, t=5.0824, P<0.001, N=24). We then focused
primarily on correlations between capture time and geometric
variables. There was no difference in capture time between
stage 2 larvae and stage 3 larvae (W=38.5, P=0.05651, N=24).
Once the prey had fallen into the trap, the capture cost was
totally independent of the size of the trap. Indeed, capture cost
was not correlated with trap diameter (r=0.1846, t=0.8812,
P=0.3878, N=24) or trap height (r=–0.0616, t=–0.2894,
P=0.7750, N=24). Capture time was negatively correlated with
angle (r=–0.5545, t=3.1254, P<0.001, N=24) and positively
correlated with RMSE (r=0.6793, t=4.3416, P<0.001, N=24).
0 2 4 6 8
0 2 4 6 8
Δ
angle
(deg.)
A
Off-centring (mm)
Δ
RMSE
(mm)
B
0
0.1
0.2
0.3
0.4
0.5
12
10
8
6
4
2
Fig.·3. Changes in
angle
(A) and
RMSE
(B) as a function of off-
centring. The straight line corresponds to the linear model fitted on
the data. The open circles are data points and the closed circles are the
predicted values of
angle
and
RMSE
in the absence of off-centring,
making it possible to obtain RMSE
wo
and
wo
: RMSE
wo
=
RMSE
(0)+RMSE
c
and
wo
=
c
angle
(0).
THE JOURNAL OF EXPERIMENTAL BIOLOGY
3514
Capture time was also correlated with off-centring (r=0.8992,
t=13.3903, P<0.001, N=24), and this relationship was
expressed in terms of a linear model (R
2
=0.8085, F=92.9,
P<0.001, N=24) (Fig.·5). The intercept of this regression line
was not significantly different from zero (intercept=
–0.5154±0.3571s, t=–1.443, P=0.163, N=24). Thus, a capture
time of zero can be obtained only if there is no off-centring (i.e.
the trap must be perfectly conical).
Discussion
Off-centring is the distance between the head and the lowest
point of the trap. This off-centring is the result of post-
construction actions: after constructing its trap, the animal
moves, triggering one or several avalanches of various sizes.
Off-centring therefore leads to a deviation from the perfect
cone shape and a decrease in trap angle as a result of the
A. Fertin and J. Casas
avalanches. Greater off-centring is associated with more
frequent and/or larger avalanches, leading to a simultaneous
decrease in angle and increase in RMSE. The loss of conicity
indicates deviations from a perfect conical surface due to dips
and humps in the trap surface. A loss of smoothness of the trap
surface may make it easier for the prey to climb back up the
trap. Similarly, the angle of the slope may affect the
displacement of the prey (Botz et al., 2003). This would explain
why off-centring affects capture cost: the prey arrives at a point
out of reach of the mandibles of the antlion and can move about
more easily within the trap. Off-centring therefore seems to be
the key factor determining predation cost. Thus, off-centring
leads to a loss of architectural efficiency that is compensated
for by attack behaviour.
We can now revisit our hypothetical model of costs and
benefits of the pit construction on the basis of our results
(Fig.·1). In the absence of off-centring, the trap is perfectly
conical and the angle (
wo
) is significantly smaller than that
defined by the physics of sand (
c
). Thus, before off-centring,
the antlion constructs a trap that is perfectly conical but has an
angle smaller than the crater angle. The angle
wo
therefore
corresponds to the shallowest slope allowing prey to be
captured as efficiently as possible. The antlion gains no
advantage in terms of efficiency from building a trap with an
angle greater than
wo
. Any perturbation leading to avalanches
leads to higher maintenance cost. Thus the slope angle targeted
by the antlion can be somewhat shallower than the crater angle.
As described in the Introduction, the animal constructs its trap
by defining an initial diameter and then digging down in a spiral
to the bottom of the funnel (Tuculescu et al., 1987; Youthed
and Moran, 1969). The creation of perfect traps requires that
the antlion begins with an initial perfect circle, digs itself down
with a spiral movement, and stops before reaching the crater
angle. We do not know the stimuli used for making this
decision, but the production of avalanches and/or the forces
acting on the numerous mechanosensors on the body may be
used.
Pits are the simplest possible type of trap, and their rarity
remains puzzling (Hansell, 2005). This foraging strategy is not
new. These insects changed habitat before the fragmentation
of Gondwana, moving from the trees to sand (i.e. from
arboreal life style to psammophily) and pit construction was
the key to the emergence of a small but successful group
within the Myrmeleontidae, the Myrmeleontini (Mansell,
1996; Mansell, 1999). Other groups that developed later,
including the Palparini, did not adopt this strategy, but have
also been successful. Pit construction does not require specific
morphological adaptations. Wormlion larvae (Diptera,
Vermileonidae, Vermileo), which have no legs or strong
mandibles, also construct pits in sand (Wheeler, 1930). Thus,
insect larvae of all morphologies are potentially able
to build such traps. Finally, the type of prey and the
microhabitat requirements are not necessarily unusual or
restrictive in any way. It therefore remains a mystery why such
simple traps have so rarely been adopted by the animal
kingdom.
An
g
le (de
g
.)
14
12
10
8
6
4
2
0
Frequency
28 30 32 34 36 38 40 42
α
c
α
wo
Fig.·4. Distribution of the angles achieved in antlion constructions.
The number of classes is given by Yule’s formula (k=5.53). The bars
with solid lines correspond to
wo
and
c
, and the dotted lines indicate
the 95% confidence intervals for these angles.
02468
Off-centrin
g
(mm)
8
6
4
2
0
Capture time (s)
Fig.·5. Linear changes over time in capture as a function of off-
centring.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
3515Antlion trap construction
List of abbreviations
angle with respect to the horizontal of the trap
RMSE root mean square error
c
drained angle of repose by a crater
RMSE
c
root mean square error by a crater at
c
angle
difference between
c
and trap angle
RMSE
difference between trap RMSE and RMSE
c
wo
theoretical angle without off-centring
RMSE
wo
theoretical RMSE without off-centring
We would like to thank three anonymous reviewers for their
instructive comments on the first version of this manuscript, as
well as Olivier Dangles and Sylvain Pincebourde. This work is
part of the PhD thesis of A.F. financed by the Ministry of
Higher Education and Research.
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THE JOURNAL OF EXPERIMENTAL BIOLOGY
... Antlion larvae readily catch the attention of naturalists by virtue of their innate pit digging behavior and trapping. The pit is constructed by the animal moving backward, digging using the teeth or pegs on the distal abdominal segments [21]. The larva is selective in the choice of site for pit construction, which is often a shaded sandy area. ...
... The larva should, therefore, be able to assess the site. The factors that influence pit building are the size of the sand particles, shade, and humidity [21]. The sand provides a good medium for the conduction of vibrations. ...
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Benzene, a ubiquitous environmental chemical, is known to cause immune dysfunction and developmental defects. This study aims to investigate the relation between benzene‐induced immune dysfunction and developmental toxicity in a genetically tractable animal model, Drosophila melanogaster. Further, the study explored the protective role of Heat Shock Protein 70 (Hsp70) against benzene‐induced immunotoxicity and subsequent developmental impact. Drosophila larvae exposed to benzene (1.0, 10.0, and 100.0 mM) were examined for total hemocyte (immune cells) count, phagocytic activity, oxidative stress, apoptosis, and their developmental delay and reduction were analyzed. Benzene exposure for 48 h reduced the total hemocytes count and phagocytic activity, along with an increase in the Reactive Oxygen Species (ROS), and lipid peroxidation in the larval hemocytes. Subsequently, JNK‐dependent activation of the apoptosis (Caspase‐3 dependent) was also observed. During their development, benzene exposure to Drosophila larvae led to 3 days of delay in development, and ~40% reduced adult emergence. Hsp70‐overexpression in hemocytes was found to mitigate benzene‐induced oxidative stress and abrogated the JNK‐mediated apoptosis in hemocytes, thus restoring total hemocyte count and improving phagocytotic activity. Further, hsp70‐overexpression in hemocytes also lessened the benzene‐induced developmental delay (rescue of 2.5 days) and improved adult emergence (~20%) emergence, revealing a possible control of immune cells on the organism's development and survival. Overall, this study established that hsp70‐overexpression in the Drosophila hemocytes confers protection against benzene‐induced immune injury via regulating the ROS/JNK signaling pathway, which helps in the organism's survival and development.
... Antlion larvae readily catch the attention of naturalists by virtue of their innate pit digging behavior and trapping. The pit is constructed by the animal moving backward, digging using the teeth or pegs on the distal abdominal segments [21]. The larva is selective in the choice of site for pit construction, which is often a shaded sandy area. ...
... The larva should, therefore, be able to assess the site. The factors that influence pit building are the size of the sand particles, shade, and humidity [21]. The sand provides a good medium for the conduction of vibrations. ...
Article
Most of the pit-building larvae of antlions display an interesting behavior of pit construction by digging sand and building it in a conical shape. The larva then sits at the apex, waiting for the prey to fall down the slope of the funnel. Vibrations detect the prey in the sand, which is used as a cue to orient and throw sand to knock down the prey. The sensory structure involved in this biological function is analyzed in the current study. The antenna and labial palp have a small number of sensilla meant for chemoreception and possibly hygro-reception. Eyes appear reduced with only six stemmata on a tubercle. In keeping with the subterranean mode, the sensilla chaetica (SC) on the 'jaws' are stunted, and sensilla trichoid are lacking. An assembly of four campaniform sensilla at the base of the jaws may provide sensory feedback during sand tossing and feeding. The antenna that lacks hairs on its antennomeres is remarkably long for an insect larva. Thus larvae have limited chemosensory capabilities compared to adults. The mechanoreceptors sensilla chaetica and antennae may help to locate prey.
... The predation strategy of antlion larvae consists in the construction of funnel-like pits to capture prey [3][4][5]. The larva's abdomen is used as a hoe to excavate sandy soil and the mouth to cast sand out from the pit [6]. ...
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This study aimed to investigate the diversity of ants captured in Myrmeleon pits in a Cerrado environment (Brazilian savanna) and assess the relationship between pit size and capture success. Field expeditions were performed in the Inhamum Municipal Environmental Protection Area, Caxias, Maranhão State, Brazil. Pits of Myrmeleon larvae were observed, and captured ants were collected and identified. Our results showed that Myrmeleon larvae inhabiting this Cerrado site rely on ants as their main natural prey. Seven ant species were identified. There was a positive relationship between pit diameter and capture success. This is the first investigation of the diversity of ants naturally predated by antlions.
... However, a fundamental understanding of the relationship between a granular surface and a simple object (such as a sphere) has not been sufficient. Investigation of such a fundamental relation could also relate to the ecology of antlions that use the stuck phenomena to prey on ants [7,8]. It would also relate to groove formation on planetary granular surfaces. ...
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We experimentally investigate the dynamics of a sphere rolling up a granular slope. During the rolling-up motion, the sphere experiences slipping and penetration (groove formation) on the surface of the granular layer. The former relates to the stuck motion of the rolling sphere, and the latter causes energy dissipation due to the deformation of the granular surface. To characterize these phenomena, we measured the motion of a sphere rolling up a granular slope of angle α. The initial velocity v0, initial angular velocity ω0, angle of slope α, and density of the sphere ρs were varied. As a result, the penetration depth can be scaled solely by the density ratio between the sphere and granular layer. By considering the rotational equation of motion, we estimate the friction due to the slips. Besides, by considering energy conservation, we define and estimate the friction due to groove formation. Moreover, the translational friction is proportional to the penetration depth. Using these results, we can quantitatively predict the sphere's motion including stuck behavior.
... Because of their complex nature [4], interactions with granular materials offer a rich field of study. In nature, solidfluid transitions in granular media are masterly exploited by the antlion larvae in order to catch prey [5][6][7]; they dig a conical pit into the sand and wait at the bottom for their victims to fall down. In fact, for most of the antlion's prey, locomotion on the inclined pit walls represents an insurmountable challenge. ...
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Locomotion on granular inclines is a subject of high relevance in ecological physics as well as in biomimmetics and robotics. Enhancing stability on granular materials represents a huge challenge due to the fluidization transition when inclination approaches the avalanche angle. Our motivating example is the predator-prey system made of the antlion, its pit, and its prey. Recent studies have demonstrated that stability on granular inclines strongly depends on the pressure exerted on the substrate. In this work we show that for multilegged locomotion, along with pressure, the distance between the leg contacts on the substrate also plays a major role in the determination of the stability threshold. Through a set of model experiments using artificial sliders, we determine a critical distance below which stability is importantly affected by the interactions between the perturbed regions generated by each contact point. A simple model based on the Coulomb method of wedges allows us to estimate a stability criterion based on pressure, interleg distance, and substrate characteristics. Our work suggests that mass to leg-length allometric relationships, as the ones observed in ants, may be an important key in determining the locomotion success of multilegged locomotion on granular inclines.
... Finally, granular media such as soil and sand are present in a huge range of environments like deserts, seashores and underwater substratesall of which are densely inhabited by diverse panarthropod species. Many predators have also evolved strategies to exploit these locomotive challenges to catch insect prey: for example, the slippery peristome of carnivorous plants (Bohn and Federle, 2004) and sandy antlion pits (Fertin and Casas, 2006). ...
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Panarthropods (a clade containing arthropods, tardigrades and onychophorans) can adeptly move across a wide range of challenging terrains and their ability to do so given their relatively simple nervous systems makes them compelling study organisms. Studies of forward walking on flat terrain excitingly point to key features in inter-leg coordination patterns that seem to be 'universally' shared across panarthropods. However, when movement through more complex, naturalistic terrain is considered, variability in coordination patterns - from the intra-individual to inter-species level - becomes more apparent. This variability is likely to be due to the interplay between sensory feedback and local pattern-generating activity, and depends crucially on species, walking speed and behavioral goal. Here, I gather data from the literature of panarthropod walking coordination on both flat ground and across more complex terrain. This Review aims to emphasize the value of: (1) designing experiments with an eye towards studying organisms in natural environments; (2) thoughtfully integrating results from various experimental techniques, such as neurophysiological and biomechanical studies; and (3) ensuring that data is collected and made available from a wider range of species for future comparative analyses.
... The singularity of this foraging strategy has long drawn attention to these insects (Fertin & Casas, 2006;Scharf et al., 2011). The larva remains motionless buried at the bottom of the pit with its mandibles open, awaiting the prey to fall into the trap. ...
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Seasonality in the Cerrado biome of Brazil is characterized by a dry season and a rainy season, affecting the availability of water and generating nutritional limitations. Thus, plants and animals have developed adaptive mechanisms in order to survive in this environment. Insects known as antlions (Neuroptera: Myrmeleontidae) occur in areas of the Cerrado and build traps in dry soil to capture prey items. In the rainy season, these insects are unable to forage due to the waterlogged soil. The aim of this study was to investigate the influence of the rainfall regime in the Cerrado on aspects of trap-building behavior, larval development and morphological characteristics of adult antlions. Larvae of the antlion Myrmeleon brasiliensis (Návas, 1914) were observed and collected in an area of the Cerrado biome in the municipality of Aquidauana (MS), Brazil. Observations were performed in the rainy and dry seasons to determine the abundance of traps built by M. brasiliensis larvae. In the laboratory, experiments were performed involving the manipulation of the frequency of simulated rain on the traps. The results revealed that variations in rainfall due to seasonality in the Cerrado affect M. brasiliensis larvae, with greater foraging observed in the dry season. The laboratory experiments demonstrated that differences in the frequency of rains affect the mortality of the larvae, larval development time and the size of the adults. Thus, variations in rainfall patterns can lead to variations in the characteristics of the population structure of M. brasiliensis in areas of the Cerrado biome in Brazil. KEYWORDS. Antlion; seasonality; trap-building behavior; tropical insects
... The adult lives for about a month, as a predator that forages in the night, hunting small insects, such as butterfly larvae. The adults in Denmark occur from the end of May until the start of September, with some slight variation between species, as seen by their seasonal flight patterns (Figure 4) (Arnett and Gotelli 1999;Fertin and Casas 2006;Nielsen 2015). ...
Article
Three species of Myrmeleontidae are currently known from Denmark: Myrmeleon bore, Myrmeleon formicarius and Euroleon nostras. Despite their unique and interesting life history, the faunistics of antlions in Denmark are in need of an update. Here, we primarily use the collections from the Natural Museum of Denmark and the Natural History Museum Aarhus to document the species distribution and richness. The antlion specimens were databased according to the distribution data, and distribution maps were created for each species. The maps are compared to previous analyses of Danish antlion faunistics as well as available online sources. The occurrence of the species in neighbouring countries is also considered. Identification keys to both larvae and adults of the Danish species are provided. Interspecific competition could explain why some locations only contain one species. In Denmark, there seems to be a marked correlation between the occurrence of antlions and the presence of aeolian sand. Aeolian sand is an excellent substrate for the larval funnels and is probably the core habitat of the antlion species occurring in Denmark.
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Traps are an efficient method of capturing prey for ambush predators, but trap building and maintenance are costly. We describe suitable hunting sites for pit-building antlion larvae living in sand dunes based on its cost–benefit relationship. In the field, antlion pits were located near natural barriers, such as cliffs, rocks and vegetation, but not closest to these barriers. Our results show that this pattern of pit location did not differ between populations; neither with or without the influence of a specific dipteran parasitoid of antlion larvae. Artificial pitfall traps deployed in their habitats revealed that invertebrates move along barriers, likely through thigmotaxis (wall hugging or wall-following), and drop sands in the traps set at barrier edges. In the laboratory, repeated artificial destruction of pits from larval antlions induced frequent pit relocation and rebuilding. This task reduces life history parameters, such as the larval growth and food conversion rates, suggesting a high cost of pit maintenance. Thus, antlion pits might shift away from barrier edges where more prey is available but pit destruction occurs more frequently due to wall-following invertebrates. Such disturbance may explain why antlions are not located closest to these barriers.
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The relationship between web design and prey capture in orb-web spiders was examined by correlating the mean mesh height with the mean prey length per species taken from existing literature (15 species) and new data (Larinioides sclopetarius and Argiope keyserlingi). Pooling the data from all species, the results revealed no significant relationship. Analysing the data from L. sclopetarius and A. keserlingi separately, no overall significant relationship was found. However, the analyses of the separate observation days showed that mesh height correlated significantly with prey length on one of the five observation days for A. keyserlingi, but not for L. sclopetarius. Consequently, the spacing of the sticky spiral in the orb-web can have a significant effect on the length of the captured prey under certain circumstances, which are discussed in the present paper.
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Forest-understory, orb weaving spiders display at least two, alternative, foraging modes. Large spiders build one large web per feeding period. Although their webs intercept more prey than webs built by small spiders, the biomass of captured prey relative to spider biomass is low. In contrast, small spiders build three to five webs per feeding period. The ratio of prey biomass intake relative to spider biomass, however, is high. Small spiders may be able to tolerate high rates of web loss because of their potentially high rate of prey intake. However, for large spiders, the high rates of web loss may not be tolerable because of the low rate of prey biomass intake. This work shows that orb weaving spiders forage differently and that different patterns of web use have resulted in at least two very different, but equally effective, means of prey capture.
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The predatory behavior of a pit-making antlion, Myrmeleon mobilis, is characterized. Behavioral sequences among three prey types were similar, when compared via flow diagrams. A significant difference in behavioral frequency existed between hardbodied and soft-bodied prey types.
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This paper reviews the known cases of the use of tools by animals feeding under natural conditions and discusses the possible origins, transmission, and subsequent evolution of this behavior. It seems probable that the pioneer tool-users of various species were simply using pre-existing behavior patterns in a way which accidentally involved the use of an object as a tool. The transmission of the trait in some populations of birds and mammals may have taken place fairly rapidly if inexperienced animals could benefit from observation of tool-using parents or companions. In the relatively few cases where the use of tools makes a substantial contribution to the food economy of a species selection for facility in tool-using may be evident. This may have taken the form of shifts in thresholds for selected behavior patterns in the insect and fish tool-users or it may have led to special learning abilities in the bird and mammal tool-users. Comparative studies of this behavioral trait may contribute to an understanding of human evolution. Sea otters, woodpecker finches, and humans may be especially proficient in the use of feeding tools because all have invaded unusual niches for their phylogenetic groups and have faced potentially severe competition from species well established in their environments. Under these circumstances selection may operate at a variety of levels to improve the tool-using abilities of populations of animals.
Article
(1) The general feeding biology of Morter obscurus is described. (2) First instar larvae, because they use a different pit construction technique, have steeper-walled pits than later instars. Pit diameter and larval length are linearly related. (3) Capture success is determined mainly by the relative sizes of predator and prey. For a given relative size instar 1 larvae are more successful because of the steep-walled pits. Capture success drops to zero when ants can place some of their legs outside the pit. Third instar larvae were more successful than second instar larvae in pits of the same size. Capture success, particularly for large larvae, is 100% over much of the prey size range. (4) Successful attacks on ants with thick exoskeletons occurred almost exclusively via the gaster whereas mandible insertion for ants with thin exoskeletons frequently occurred elsewhere. (5) Differences in pit morphology and prey capture behaviour in Macroleon lynceus are documented and related to habitat differences. In Morter, pit morphology is crucial for prey capture, while strength is more important for the larger Macroleon. (6) Handling time was divided into time to capture (Tc), time to death (Td), and time to extract body contents (Te). Tc was constant for small prey but increased rapidly for larger prey. Td was constant for all sizes of predator and prey. Te increased with prey size and decreased with increasing predator size and temperature. Te seems to depend not only on the amount of extractable food but also on the shape of the victim. (7) Hunger has no effect on prey handling time or food extraction efficiency. However hungry larvae are more likely to move their pits. Ant-lions can capture prey falling into the pit when already feeding and so increase their food supply. (8) Growth rates of larvae feeding on different sized prey were measured. Large larvae grew more slowly than small ones when fed on the same sized prey because of higher maintenance costs. For a given sized predator, growth per unit weight of prey received declined with increasing prey size because of increased feeding costs. Each size of ant-lion had a prey size for which the costs per unit return were a minimum, this size changing abruptly from very small prey for the first two instars to large prey for the final instar. (9) The feeding biology of the three instars is compared and contrasted. First instar larvae are adapted to achieve a high capture success rate on a small prey size range because feeding costs are high and escapes therefore expensive. For large larvae, maintenance costs are more important and selection has favoured a large size range of catchable prey. While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.