2005. The Journal of Arachnology 33:516–522
THE WASP SPIDER ARGIOPE BRUENNICHI
(ARACHNIDA, ARANEIDAE): BALLOONING IS NOT AN
OBLIGATE LIFE HISTORY PHASE
Andre´ Walter, Peter Bliss
and Robin F.A. Moritz: Institut fu¨r Zoologie, Martin-
Luther-Universita¨t Halle-Wittenberg, Hoher Weg 4, D-06120 Halle (Saale), Germany.
ABSTRACT. Aerial dispersal (‘‘ballooning’’) of Argiope bruennichi spiderlings has been claimed to be
an obligate life history trait and a prerequisite for spinning prey-capture webs. If this were true, a bal-
looning phase would be essential for any laboratory rearing of A. bruennichi making rearing protocols
particularly elaborate. We tested the signiﬁcance of ballooning for second-instar spiderlings in the labo-
ratory and showed that the ballooning behavior is not essential for building prey-capture orb webs. Our
results also give no evidence for the hypothesis that recent natural selection has changed ballooning
behavior in newly founded ﬁeld populations.
Keywords: Araneae, ballooning experiment, laboratory rearing, web-building behavior.
Ballooning is a common dispersal mecha-
nism for many modern spiders (Coyle 1983;
Dean & Sterling 1985; Weyman 1993), and
this behavior is particularly important for
maintaining genetic cohesion among Argiope
populations (Ramirez & Haakonsen 1999).
The life history of Argiope is characterized by
ballooning, the aerial transport on wind-blown
silk threads. A good example for the impor-
tance of ballooning for range expansion is the
Palearctic wasp spider Argiope bruennichi
(Scopoli 1772). The spider is an r-strategist
(Guttmann 1979), characterized by high aerial
dispersal capability and an ongoing postgla-
cial expansion of its geographical range in Eu-
rope (van Helsdingen 1982). Females of A.
bruennichi produce up to ﬁve cocoons in the
ﬁeld, often containing several hundred eggs
(Crome & Crome 1961; Ko¨hler & Scha¨ller
1987). The expansion of the species has ac-
celerated in the second half of the last century
probably due to factors favoring dispersal by
ballooning (Guttmann 1979; Levi 1983; Sach-
er & Bliss 1990; Scharff & Langemark 1997;
Jonsson & Wilander 1999; Smithers 2000).
The wasp spider prefers grassy or herbaceous
vegetation in open, ephemeral or shrubby sites
(Wiehle 1931; Pasquet 1984; Malt 1996) in
coarse-grained (patchy) landscapes (Gillandt
& Martens 1980; Sacher & Bliss 1989) and
has regionally beneﬁted from an extension of
farming production and urbanization (Loh-
meyer & Pretscher 1979; Arnold 1986; Nyf-
feler & Benz 1987). River valleys have been
identiﬁed as favored dispersal corridors fur-
ther supporting the importance of ballooning
for dispersion (Gauckler 1967; Puts 1988).
Follner & Klarenberg (1995) claimed bal-
looning to be an obligate phase in the devel-
opment of A. bruennichi. These authors mon-
itored the pre-ballooning and ballooning
behavior of spiderlings in a grassland study
site near Munich (Germany). Since they never
found aggregations of orb webs in the neigh-
borhood of the cocoons from which the over-
wintering second instar spiderlings eclosed
and they only observed the construction of
ﬁrst prey-capture orb webs after a ballooning
trip, they concluded ‘‘that aeronautic behav-
iour in Bavarian populations of A. bruennichi
is obligatory’’. Moreover, these authors sug-
gested that spiderlings, which have hatched
from the cocoon, will starve to death, unless
they perform a ballooning trip. Ballooning
should thus be an obligate phase to switch
from a non-predatory, passive phase to one of
active predation by spinning prey-capture
orbs. Follner & Klarenberg (1995) argued that
the obligatory aerial dispersal might be a re-
sult of recent natural selection and be the rea-
517WALTER ET AL.—BALLOONING IN ARGIOPE BRUENNICHI
Figures 1–4.—Design and course of the ballooning experiment. The spiderlings were placed on a spatula
(sp) and exposed to a light air current by a fan (ve) and heat source (hs), which were placed at the left
edge of a lab bench (240 cm). After cutting the drag line the spiderlings became airborne to land on the
lab bench, which served as a landing strip (ls). 1. Pre-ballooning behavior: sp
(light breeze); hs
heat source (25 Watt lamp, distance to spatula
20 cm); sh
from a dragline; bt
ballooning thread. 2. Initial ballooning phase. 3. Airborne spiderling: ls
strip’’ (lab bench of 240 cm length). 4. Landing phase.
son behind the swift expansion of the species.
New populations which are established during
a period of expansion are always founded by
individuals, which have ballooned.
If ballooning were a truly obligate phase, it
would not only be important for natural selec-
tion but also be important for any rearing pro-
tocol for A. bruennichi. Allowing for balloon-
ing in a rearing procedure might easily render
laboratory breeding unfeasible as it could
prove to be too time-consuming and laborious.
However, an obligate ballooning phase has
never been observed before, neither in other
Argiope nor in the generally well studied A.
bruennichi. Tolbert (1976, 1977) studied bal-
looning behavioral elements of A. trifasciata
(Forska˚l 1775) and A. aurantia Lucas 1833.
He concluded from ﬁeld and laboratory ob-
servations that ‘‘it is unnecessary for spider-
lings of either Argiope species to engage in
aerial dispersal before building an orb web’’
(Tolbert 1977), which is an obvious discrep-
ancy to Follner’s and Klarenberg’s (1995)
claims. We here test the signiﬁcance of bal-
looning for the construction of the ﬁrst prey-
capture web in the laboratory by comparing
spiderlings reared under two experimental
conditions, one with and one without balloon-
We collected cocoons of A. bruennichi (n
6) in dry and semi-dry grasslands north-
east of Halle (Saale) in late April 2002 (Ger-
many, 160 m a.s.l., 51
E). They were maintained in the lab in indi-
vidual glass vials (9 cm diameter, 13 cm
height, coated with ﬁne gauze) at 23
and mist-sprayed with water every two days
to avoid desiccation. The vial bottom was
covered with initially wet cellulose wadding
(1 cm). Second-instar spiderlings hatched
from the cocoons in early May.
One day after hatching we simulated indi-
vidual ballooning for 60 spiderlings (10 from
each cocoon) by exposing the spiderling on a
spatula to an air stream generated by a heat
source and a fan (see Figs. 1–4 for details of
the experimental design). We observed behav-
ioral elements in the pre-ballooning phase in
detail and noticed its mode. When the spider-
ling became airborne, we tracked it and re-
trieved it at the ‘‘landing strip’’ (Figs. 3, 4).
The ballooning experiment was repeated im-
mediately (re-ballooning) for each individual
to satisfy a possible ‘‘ballooning drive’’ (see
Tolbert 1977). The spiderlings had to actively
participate in this experiment by showing the
entire sequence of pre-ballooning and bal-
looning behavior (Figs. 1–4).
Following the experiments, the ‘‘balloon-
ers’’ were kept in the same unheated indoor
room with windows admitting indirect natural
light. They were housed in groups (n
in three gauze covered glass terraria (50
31 cm; 25
10% RH) and fed
ad libitum 45–50 live Drosophila melanogas-
ter once a day. Every two days we sprinkled
the inside surfaces of the terraria with water.
This prevented desiccation and allowed for
518 THE JOURNAL OF ARACHNOLOGY
Figure 5.—Web-building activity of the A. bruennichi spiderlings during laboratory rearing for both
ballooners and non-ballooners.
normal drinking behavior of the spiderlings.
The bottoms of the terraria were covered with
a layer of commercial, pasteurized potting soil
(3 cm) with grass tufts, some dry twigs and
wooden skewers to enhance the number of po-
tential attachment points for web building.
A control group of spiderlings (n
treated in the same way, but without the bal-
looning procedure (‘‘non-ballooners’’). In
both groups (ballooners vs. non-ballooners)
spiderlings and orb webs were noted three
times daily at 6 a.m., 12 p.m. and 6 p.m. to
ensure individual based data sets. The rearing
period was cut off after 19 days when all the
surviving individuals had spun their ﬁrst prey-
Voucher specimens are deposited in the En-
tomological Collection of the Martin-Luther-
University Halle-Wittenberg (Zoological In-
stitute), Germany (identiﬁcation number
The web-building activity of the spiderlings
increased in both the ballooners and the non-
ballooners over time and reached 90
54, three terraria) and 95
5% for non-ballooners (n
57, three terraria)
within a period of 19d (Fig. 5). The differ-
ences in the web-building activity (Fig. 5)
were not statistically signiﬁcant between the
two groups of spiderlings (Kruskal-Wallistest,
0.7515; tested for daily built-ﬁrst webs).
The mean latency time for web-building (time
from hatching from the cocoon to the con-
struction of the ﬁrst prey-capture web) was
4.28 days and 8.18
3.60 days for
54) and non-ballooners (n
57) respectively. This difference was not sta-
tistically signiﬁcant (t-test, P
Although mortality increased in the second
half of the observation period (Fig. 6), it did
not exceed 22% at the end of the experiment
12, difference not
signiﬁcant, t-test, P
0.77). The surviving
animals caught prey in their orb webs and
showed normal development with up to four
molts within the experimental time.
Using our protocol, we could initiate the
full sequence of ballooning behavior promptly
in every experiment. The A. bruennichi spi-
derlings always showed an identical sequence
of pre-ballooning and ballooning behavior
(Fig. 1–4). When exposed to the heat from the
lamp, they displayed the ‘‘ballooning drive’’
519WALTER ET AL.—BALLOONING IN ARGIOPE BRUENNICHI
Figure 6.—Mortality of the A. bruennichi spiderlings during laboratory rearing.
behavior. Individuals walked to the margin of
the spatula, spooled out a dragline and
dropped down hanging from the line. While
suspended and holding on to the drag line,
they let out an additional line of 50–100 cm
ballooning silk (Fig. 1). When this was lifted
by the breeze generated by the fan and the
heat source, the spiderlings cut the dragline
and became airborne (Figs. 2, 3). After land-
ing (Fig. 4) they hauled in the ballooning line,
formed it with the legs into a silk blob and
ﬁnally ate the silk, bringing the ballooning be-
havioral sequence to completion.
Tolbert (1977) observed two modes of
preparation for ballooning in sympatric ﬁeld
populations of A. trifasciata and A. aurantia.
A spiderling attempting to become airborne
climbed to the top of some blade of grass or
other structures and adopted the typical ‘‘tip-
toe’’ posture by depressing the cephalothorax
and elevating the opisthosoma. Multiple silk
lines were then exuded from the spinnerets.
When moving air generated sufﬁcient silk, the
spiderling became a ‘‘ballooner’’ (Nielsen
1932; Richter 1970; Eberhard 1987). Alter-
natively, the spiderling could become airborne
by dropping and hanging from a dragline,
spinning a ballooning thread, which then grad-
ually lifted and lengthened in the breeze. The
ballooner then cut the dragline and ﬂoated off
into the air (Nielsen 1932; Bristowe 1939).
Argiope bruennichi can display both pre-
ballooning modes. However, the drop and
dragline mediated ballooning seems to be
more frequent (Follner & Klarenberg 1995).
In the ﬁeld, second-instar spiderlings usually
attach the draglines to tips of grass blades or
they use silk threads which connect the tips
of grass haulms as attaching points (Follner &
Klarenberg 1995). In our experiments, we of-
fered individual spiderlings optimal starting
conditions, and we never observed the tip-toe
ballooning mode. Follner (1994) suggested
that ‘‘tip-toe’’ might be a tactical alternative
for individuals in unfavorable starting points
(e.g., overcrowded tips of grass blades).
Our results show that it is not necessary for
spiderlings of A. bruennichi to engage in ae-
rial dispersal before building a prey-capture
web. While ballooning is frequent in the ﬁeld
(Follner & Klarenberg 1995), it is clearly not
an obligate part in the development of this
species. In spite of the rapid expansion of the
species over the past decades and the potential
importance of aerial dispersal for colonizing
new habitats, the role of ballooning in A.
520 THE JOURNAL OF ARACHNOLOGY
bruennichi does not differ from A. trifasciata
and A. aurantia where this phase in life his-
tory is also not obligate (Tolbert 1977).
The mortality of about 20% after 19 days
in both experimental groups (difference statis-
tically not signiﬁcant) suggests that rearing of
A. bruennichi spiderlings to adulthood may be
challenging. Our rearing method based on a
diet with Drosophila melanogaster, similar to
Mu¨ller & Westheide (1993), worked well for
our purpose, where we only tested the effects
of ballooning in second-instar spiderlings on
their ability to make their ﬁrst web.
On average, more then eight days elapsed
before A. bruennichi spiderlings began to
build their ﬁrst prey-capture web. This ap-
pears to be a surprisingly long period, because
the animals can only feed once the ﬁrst web
is built. We cannot exclude that this is a lab-
oratory artifact, for example due to unattrac-
tive sites for web construction. However, the
long latency did not interfere with the rearing
regime. The animals appeared to be well
adapted to temporary starvation because the
mortality was low in this phase (Fig. 6). Also
in the ﬁeld, the spiderlings do not immediately
start with prey-capture web construction (Foll-
ner & Klarenberg 1995) and endure extended
periods of starvation. Argiope spiderlings eas-
ily survive several days nearby their cocoons,
sometimes with communal meshworks of in-
terlocking dragline threads (‘‘communal tan-
gles’’) (Tolbert 1976, 1977; Follner & Klar-
enberg 1995) where they ﬁnd shelter until
favorable weather or microclimate conditions
allow for ballooning (Tolbert 1977; Follner &
Klarenberg 1995; see also Suter 1999 for
physics of ballooning).
Argiope spiderlings actively select suitable
web sites by ballooning, re-ballooning or
walking (Enders 1973; Tolbert 1977; Follner
& Klarenberg 1995). Also in this nonpreda-
tory phase the spiderlings must avoid starva-
tion. Tolbert (1976) kept A. aurantia spider-
lings in the laboratory without food and water.
Mortality remained moderate in these experi-
ments for several days and only increased dis-
tinctly about two weeks after hatching.
The behavioral ballooning sequence could
be easily triggered under artiﬁcial conditions
in our study, suggesting that it will also occur
in the ﬁeld whenever environmental condi-
tions allow. Therefore dispersal and popula-
tion structure will be primarily driven by mi-
croclimatic conditions in the local habitats.
The local persistence of non-emigrants (non-
ballooners and short-distance ballooners) in A.
bruennichi populations might facilitate aggre-
gated dispersion patterns, just as in weather
phases which are unfavorable for aerial dis-
persal. Given ballooning is a less effective
means of long distance dispersal than previ-
ously thought (Roff 1981; Decae 1987; Wise
1993; Bonte et al. 2003), this could also ex-
plain the genetic differentiation among habitat
patches in other Argiope species (Ramirez &
The role of natural selection in range ex-
pansion has recently been discussed for in-
sects in the context of global warming (e.g.,
Pimm 2001; Thomas et al. 2001). However,
improving environmental conditions at range
margins can initiate range extensions purely
on the basis of ecological, physiological and
population-dynamic processes not requiring
any evolutionary change (Thomas et al. 2001;
see also Coope 1995; Williamson 1996). Our
results are in line with these views and reject
the hypothesis of Follner & Klarenberg (1995)
that evolutionary processes have changed bal-
looning behavior in newly founded popula-
We are grateful to Peter Neumann, Gail E.
Stratton and two anonymous reviewers for
helpful comments on previous drafts of the
manuscript. We thank Christian W.W. Pirk for
statistical advice, Vlastimil Ru´zˇicka and Theo
Blick for providing literature. This study was
supported by a research fellowship to A.W.
from the State of Saxony-Anhalt and by the
Deutsche Forschungsgemeinschaft (DFG)
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Manuscript received 17 September 2004, revised 10