Visual mimicry is
targeted at vertebrate predators - primarily birds and small
reptiles. Butterflies and moths also use mimicry to protect
themselves against insect predators, but in this instance chemical
rather than visual mimicry is used.
Take for example
the case of a caterpillar such as that of the Large Blue
Maculinea arion, which is carnivorous
during the latter part of its life, feeding on ant grubs within the
underground nests of Myrmica sabuleti
ants. The caterpillar had to evolve a way of protecting itself from
the aggressive adult ants. It does this partly by appeasing the ants
with 'gifts' of sugary fluids that it exudes from a dorsal
'newcomers gland', and partly by emitting chemical odours that fool
the ants into thinking that the caterpillar is another ant.
The study of this
pheromonal mimicry in butterflies is still in its infancy, but it
will probably be found to be commonplace among Lycaenid butterflies,
a high percentage of which spend the larval and pupal stages of
their lifecycle in association with ants.
Manu cloudforest, 1400m, Peru ©
As in the case of
thousands of other nocturnal species, males of the wasp mimic moth
Cosmosoma myrodora are attracted by
pheromones emitted by their females. As a
myrodora male approaches a female, he hovers above her, and
discharges a burst of very fine filaments which swirl in the air
around her, and envelop her body.
Conner and Boada investigated the lifecycle and ecology of this
moth. They found that Cosmosoma males
are attracted to Eupatorium plants, and
sequestered alkaloids from juices seeping from the stems. Such
pyrrolizidine alkaloids are sequestered by a wide variety of
butterfly genera including Ithomia,
Oleria, Lycorea and
Danaus; and by several genera of moths
in the family Arctiidae. The PAs stored in the bodies of the insects
render them toxic or unpalatable to birds, and are a primary defence
method in aposematic species.
found that in the case of Cosmosoma the
toxins seemed to be directed mainly at predatory spiders. Moths
caught in the webs of Nephila clavipes
were cut free from the webs by the spider, but moths which had been
deprived of the opportunity to sequester PAs were consumed.
Conner and Boada
found that PAs were passed to females via the discharged filaments,
and also via spermatophores delivered during copulation. The PA
toxins conveyed to females were found to provide them with
protection against predators during the following nights, enabling
them to lay their eggs unmolested. It was also demonstrated that the
toxins were passed to the eggs, and provided them with protection
against ants, Coccinellid beetles ( ladybirds ) and Chrysopid
moths do not sting in the sense that a wasp or bee does, but a
significant number of species, particularly tropical ones, have
spikes or setae ('hairs') which have urticating properties. If
touched, the hairs break and release formic acid, or strong
alkaloids that can cause irritation or cause a skin rash on humans.
This type of defence is found mainly in the caterpillars of the moth
family Lasiocampidae, and is probably targeted against insectivorous
birds and small reptiles.
A much more
dangerous chemical defence system is found in the caterpillars of
Lonomia obliqua, which can be found
clustered in groups of up to 100 on tree trunks in the Amazon
rainforest. There have been numerous incidents where people have
unwittingly touched or rubbed their arm against these caterpillars.
The effects of a dose from multiple
caterpillars can be very severe, including massive intercranial
haemorrhaging and kidney failure. Lonomia
obliqua caterpillars are a frequent cause of death in
southern Brazil - 354 people died between 1989 and 2005. The
fatality rate is about 1.7% - roughly equivalent to that of
The caterpillars of several
butterflies including the Large White Pieris
brassicae will reflex-bleed if alarmed, and exude toxins from
their mouthparts. These fluids are sufficiently noxious to dissuade
insectivorous birds, which invariably drop them and then frantically
wipe their beaks to remove any trace of the toxins. A similar form
of defence is used by Pericopiine moths in South America, which
exude a hemolymph foam from their mouths and spiracles if gripped.
Any bird attempting to grip the moth in its beak will experience a
very unpleasant taste, and will instantly drop the moth, allowing it