A fellow Cornell University Entomology classmate of mine Susan Finkbeiner has done some incredible research into the previously mysterious phenomenon of butterflies roosting together at night. This roosting behavior is only found in a specialized (and very poisonous) group of butterflies in the genus Heliconius.
After months of field work in Costa Rica and Panama, her team discovered that these butterflies not only roost together on the same branch every night, but even in the same spot on the branch every night. They do this even after having been flying around all day in different areas, feeding on nectar and pollen and chasing tail, as they say.
Why do they do it?
Safety in numbers. After setting up artificial roosts with either solitary artificial butterflies or a group of them, she found that the solitary butterflies would get eaten by birds significantly more. These butterflies specialize on feeding on the poisonous, cyanide-filled passion vines. Birds will typically recognize the Heliconius as such and avoid eating them, however there are many mimicking, delicious species of butterflies that confuse the birds. This roosting behavior is unique to the Heliconius, not the mimicking species, thus birds may have learned to avoid these cuddling flyers. It would be very interesting to see if the mimicking species end up mimicking this roosting behavior as well…
This research is being covered by all sorts of international news agencies (go Susan!), including here in National Geographic.
Susan will be continuing her research on these butterflies when she passes through the Ecuadorian Amazon next month, I’m looking forward to hosting her at our base camp in the Yachana Reserve for a few solid days of butterflying.
To read her paper in full, click here.