Watch out for the wolf in sheep's clothing, they say. But what if the wolf doesn't just look like a sheep? What if it sounds like one as well?
A recent report in PLOS One finds that the wolf-and-sheep metaphor can be applied to carnivorous caterpillars and ants. Scientists from the University of Turin in Italy have discovered that large blue butterflies do a number of sneaky things during their juvenile stage. The caterpillars of the genus Maculinea are known for living off common red-elbowed ants. They exploit the ants in two ways. Some species hide out in enemy ranks and go on massive feeding sprees, while others pose as baby ants and are adopted by workers.
Sonic imitation in large blue butterflies has been known for some time. Five years ago, another team of researchers from Turin revealed that Maculinea caterpillars echo the sounds of common red-elbowed ants and their queens. The grubby predators can also give off ant odors; plus they look very much like the ant larvae. By looking, smelling, and sounding like their prey, Maculinea caterpillars are able to integrate themselves even more seamlessly within ant colonies.
What's new about the PLOS One study is that it answers why the caterpillars switch into this mode of audio mimicry. Lead author Marco Sala and his colleagues found that the caterpillars replicate sounds at multiple stages of their adolescent lives. Before broaching the nest, they start making the stridulations by rubbing one body part against another or vibrating their stomach muscles. Cuckoo-like caterpillars — larvae that try to assimilate with the colony — are better copycats because they have to keep up the ruse. Once adopted into the colony they elongate the sounds and throw more power behind them, as a way to ride up the ranks.
The aim of Sala's study was to determine how effective forgery can be when used in an ant-dominated setting. By way of playbacks and behavioral observations, Sala and his team noticed that noises that matched the queen's stridulations produced friendlier behavior in worker ants. When the ants lower their guard, the caterpillars have an advantage – one that is vital to the caterpillars' survival.
Ants use audible signals to distinguish between friends, foes, and different castes within their communities. By feigning royalty, the caterpillars are able to climb the social ladder and reap rewards that are otherwise reserved for queens. For example, workers sacrifice their food to the queen when resources are scarce. Workers will also put their lives on the line to shelter their queens from imminent danger. The caterpillars' con job thus keeps them well fed and well protected for many months, until they pupate and fly off as adults. The better their sonic mimicry, the more welfare they get from the ant community.
Large blue butterflies were once extinct in the UK. Knowing more about their larval interactions with ants can help biologists conserve and create the right type of habitat while reintroducing species throughout Europe. Now, in light of this new study, it seems that the butterflies have a chance of bouncing back. That is, as long as their caterpillars remain incognito and the ants don't catch on.
*A line was changed to read "vital to the caterpillars' survival" rather "detrimental to..."