Pattern variation is linked to anti-predator colouration in butterfly larvae

Prey animals typically try to avoid being detected and/or advertise to
would-be predators that they should be avoided. Both anti-predator
strategies primarily rely on colour to succeed, but the specific
patterning used is also important. While the role of patterning in
camouflage is relatively clear, the design features of aposematic patterns
are less well understood. Here, we use a comparative approach to
investigate how pattern use varies across a phylogeny of 268 species of
cryptic and aposematic butterfly larvae, which also vary in social
behaviour. We find that longitudinal stripes are used more frequently by
cryptic larvae and that patterns putatively linked to crypsis are more
likely to be used by solitary larvae. In contrast, aposematic larvae are
more likely to use horizontal bands and spots, but we find no differences
in the use of individual pattern elements between solitary and gregarious
aposematic species. However, solitary aposematic larvae are more likely to
display multiple pattern elements, whereas those with no pattern are more
likely to be gregarious. Our study advances our understanding of how
pattern variation, colouration and social behaviour co-vary across
lepidopteran larvae, and highlights new questions about how patterning
affects larval detectability and predator responses to aposematic prey.