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The butterfly
lifecycle
1 - Egg
- anatomy, oviposition
2 - Caterpillar
- anatomy
3
- Caterpillar
- hatching, feeding and development
4
- Caterpillar
- cannibals, carnivores and myrmecophiles
5
- Caterpillar
- survival mechanisms,
armature, camouflage / disguise
6
- Caterpillar
-
co-evolution with plants
7
- Chrysalis
- pupation, metamorphosis
8
- Adult
- emergence, feeding
9
- Adult
- mate location and courtship
10 - Adult
- daily routine, roosting, hibernation, lifespan
Larva
: survival mechanisms
Caterpillars have soft
bodies, making them extremely vulnerable to predation and
parasitism. They are unable to escape if attacked, so have evolved
numerous survival mechanisms to deal with their enemies which
include
birds, reptiles, amphibians, dragonflies,
predatory /
parasitoid wasps, robber flies,
crickets and spiders. In tropical regions they also fall victim to
ants, mantises, monkeys and numerous other threats.
Armature
Larvae in some subfamilies
e.g. Satyrinae, Hesperiinae, Notodontinae, Noctuinae,
Geometrinae and
Sphinginae are normally devoid of hairs. Those in many other
subfamilies including
Lasiocampinae,
Arctiinae, Lymantridae, Acronictinae and Hemileucinae bear hair-like
"setae". Sometimes these
are sparse but in species such as the "woolly bear" Garden Tiger
moth Arctia caja they are very long and
dense, giving the larva a furry appearance. The thick coat of hair
makes it more difficult for a bird or reptile to swallow a larva. It
also has the added bonus of cushioning it in the event of a fall.
Additionally hair
traps pockets of air around the caterpillar's body, allowing it to
survive if it has the misfortune to fall into a puddle. Caterpillars
of Arctia
caja
for example are able to survive periods
of several days submerged in water.
larva of Drinker moth
Euthrix potatoria
( Lasiocampidae ), England ©
Adrian Hoskins
The
hairs of moths in the families Lasiocampidae and Lymantridae often
have irritating properties. In the case of the Drinker moth
Euthrix potatoria
they do little more than cause a mild itch, but
the hairs shed by the larva of the Brown-tail moth
Euproctis chrysorrhoea
are rather more troublesome and can cause a
severe rash on human skin. It is generally the case however that
larvae from the temperate regions of the world are fairly safe to
handle. In the tropics it is a very different story, and all hairy
or spiky larvae should be treated with caution.
Caterpillar of Flannel moth ( Megalopygidae ), Peru ©
Adrian Hoskins
The
larvae of moths in the family Megalopygidae look fluffy and almost
invite you to handle them, but hidden beneath the soft hairs are a
series of sharp spines. If the larvae are handled the spines break,
releasing a chemical which causes excruciating pain.
Unidentified
moth larva, Peruvian Andes ©
Adrian Hoskins
Many
caterpillars, such as the unidentified species illustrated above,
use bright patterns and colours to warn enemies that they are
distasteful or poisonous. Others including those of the Nymphalinae,
Heliconiinae, Limacodidae and Saturniidae are armed with rows of
extraordinary multi-branched spikes and horns. These are enough to
deter many birds from attacking, and no doubt also offer a degree of
protection against wasps, ants and other insect predators.
Lexias pardalis,
West
Malaysia
©
Gan
Cheong Weei
Brenthis daphne,
Hungary
© Peter Bruce-Jones
Spikes, hairs
and other armature are most pronounced in young larvae which feed
communally, so it seems likely that one of their functions may be to
protect them against cannibalism.
In most species the
spines are harmless or cause only mild irritation in humans, but in
at least one Saturniidae species they can inflict a potentially
lethal sting.
The well camouflaged spiked larvae of Lonomia
obliqua are often found clustered on
tree trunks in Amazonia. There have been thousands of cases where
people have unwittingly
touching or rubbed an arm against them.
The effects can be extreme, including
massive intercranial
haemorrhaging and kidney failure.
Lonomia larvae are a frequent cause of death in southern
Brazil - 354 people died between 1989-2005.
The fatality rate is about 1.7% - roughly
equivalent to that of rattlesnake bites.
The Bullseye moth larva
Automeris liberia
( Saturniidae ) can inflict a painful sting ©
Adrian Hoskins
unidentified Limacodidae
species,
West
Malaysia
©
Gan
Cheong Weei
Larva of
Sphinx ligustri
( Sphingidae ), showing the spiracles and tail horn ©
Adrian Hoskins
Many people believe you can be stung by
the "hornworm" larvae of
moths in the family Sphingidae but this is entirely untrue. The
caterpillar is completely harmless, and edible to birds.
Mimicry
Diematic mimicry is quite
a common form of defence in caterpillars as well as in adult
butterflies and moths. The larvae of many Swallowtail species
including Papilio polymnester and
Papilio troilus have a pair of false
eye-spots on the thoracic segments. Many hawkmoth larvae such as
Deilephila elpenor and
Hippotion celerio
employ the same strategy. When alarmed the larvae of these species
puff up the thoracic segments causing the eye-spots to expand. This is
considered to be a form of diematic defence in which the larvae are
mimicking the heads of snakes.
Snake mimicry is also
found in adult Atlas moths in the genera Attacus
and Rothschildia. In these species the
forewing apex is lobed, and bears markings corresponding to the eyes
and mouth of a snake. The illusion is enhanced by rhythmic movements
of the wings which draw attention to the snake-head markings.
Camouflage and disguise
Many species use camouflage to escape detection, and are thus often
coloured green to match the leaves on which they rest.
The Lasiocampidae species illustrated
below is very well camouflaged at rest among lichens and mosses.
Others are disguised as flowers,
feathers, twigs or bird droppings.
unidentified Lasiocampidae larva, Peruvian Andes, 2800m ©
Adrian Hoskins
Generally
speaking larvae which feed as solitary individuals tend to be
palatable to predators, and rely primarily on camouflage - colours,
patterns and textures which help them to avoid detection. Larvae
which feed gregariously tend to be unpalatable or toxic to
predators. They often advertise their toxicity with bold aposematic
colours - a seething mass of brightly coloured wriggling larvae is
much more likely to deter a potential predator than a single larva
could. Gregarious behaviour also serves other purposes, e.g. a group
of larva can quickly construct a communal silk shelter in which they
can hide from predators and parasitoids. These larval shelters or
nests also protect them from the ravages of extreme weather such as
heavy rain, flooding and high winds.
Heraclides thoas, disguised as a bird
dropping. Rio Alto Madre de Dios, Peru ©
Adrian Hoskins
Multiple defence strategies
Birds rely primarily on sight to locate prey, so the evolution of
visually directed defences such as
camouflage, disguise and aposematic colouration
reduces the likelihood of larvae
being eaten.
These strategies work quite effectively against vertebrates but they
provide no protection against invertebrates such as
spiders, wasps, bugs and ants, which rely primarily on smell to locate
their prey. The larvae of many species have consequently evolved a
twin pronged defence strategy:
The larva of the Puss moth
Cerura vinula uses disguise as it's
first line of defence. When at rest its disruptive pattern of green
and dark purplish-brown gives it the appearance of a curled up leaf
with darkened edges. This illusion is reinforced by the presence of
a pair of tail prongs which are held together, simulating a leaf
stalk. The disguise helps it avoid being spotted by birds, but
offers it no protection against parasitoid wasps that track victims
down by scent. To deal with wasp attacks it switches to active
defence mode. When molested it rears up and retracts its head. This
causes the prothorax to expand, exposing a bright crimson "false
head", complete with prominent false eyes.
If this is insufficient to deter an
attacking wasp the larva then spreads its tail prongs and everts a
pair of whip-like threads which are waved angrily. Even this may not
be enough to deter a wasp however so a last resort defence the larva
can eject formic acid - the same chemical used by bees, wasps and
ants in their stings.
Most Swallowtail larvae are palatable to birds and
employ cryptic colours and patterns as their first line of defence. If
discovered however they activate additional defences. Many for example
have a pair of "false eye" markings on the thoracic segments, and can
inhale air through the spiracles to puff up the thorax, emphasising
their threatening appearance. This is often enough to deter birds from
attacking. Molestation by insect predators and parasitoids however
elicits a different response from the larvae. In this instance they
evert the "osmaterium" behind their heads. This discharges airborne
isobutyric and 2-methylbutyric acids which has been shown to repel
ants and Homopteran predators. It also deters oviposition by
parasitoid wasps and flies.
Peruvian Cattleheart larva
Parides anchises with osmaterium extended ©
Adrian Hoskins
Geometrid moth larvae use disguise as their primary
defence - they look just like tiny twigs, and reinforce this
similarity by stretching out their bodies in a straight line so that
they project twig-like from a sprig of their foodplant. If molested
they release grip on the sprig, dropping instantly from a bungee-cord
of silk. They dangle at the end of this thread until the attacker has
moved on. After a while they haul themselves back up, consuming the
silk thread as they does so.
Caterpillars of species such as the Peacock
butterfly Inachis io, the Tiger moth
Arctia caja and the Fox moth
Macrothylacia rubi try to escape when
they perceive a threat. If alarmed they simply roll into a ball and
drop to the ground. Inachis larvae are
covered in spines. Arctia and
Macrothylacia larvae are hairy. In both
cases birds remember from previous experiences that such larvae are
difficult or uncomfortable to swallow, and sight-reject them.
On the next page you can read about
the evolutionary battle for survival between plants and the
caterpillars that feed on them :
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