The Secret Lives of Social Butterflies

In a paper spent many months in the making, Susan Finkbeiner’s report on communal butterfly roosting was released to the public today. The paper closely analyzes the behavior of Heliconius, also referred to as the passion-vine butterfly, a species of tropical butterfly that exhibits curious communal tendencies. Susan seeks to learn why these insects decide to roost while several other adult butterfly species do not, begging the question “What’s the benefit of being a social butterfly?”

A Day in the Life of a Social Butterfly

A graduate student at the University of California, Irvine, Susan is also a Young Explorer Grantee. With support from National Geographic she embarked on an expedition to Panama and Costa Rica in 2011 to observe Heliconius in their natural environment- the New Word tropical rainforests.

Susan collects roosting butterfly to mark them for future identification. Photo: Abbie Dufrene

According to Susan’s study, butterfly roosting was first described by naturalist J. A. Allen in 1867 and in 1881 by W. E. Edwards. Yet even after 140 years of research, scientists are still unsure why  Heliconius repeatedly gather at a particular location in their home range to roost for the night.

With this question still unanswered, Susan brings two possibilities to the table. Her first theory hypothesizes that their unusual, gregarious behavior is actually a form of information sharing. Her second theory examines whether roosting is an anti-predator defense, similar to finding “safety in numbers”.

Up before the sun peeks above the thick tropical trees, Susan waits for the butterflies to awake. She plans to test her first theory by observing whether the butterflies follow one another from their roost to a foraging site. However, of nine independent roosts, only one butterfly was observed to have followed another to a flowering plant.

To test her second theory Susan created artificial Heliconius to observe the behavior of potential predators. Using avian-indiscriminable butterfly models, Susan noticed that when only one butterfly model was present, attempts by birds to attack it were nearly three times higher than predation attempts on roosts of five models. These findings provided compelling evidence that roosting is, in fact, an anti-predator defense.

Susan places her “fake” butterflies on a branch. Photo: Abbie Dufrene

Ensuring the Future of Passion-Vine Butterflies

By working on a group butterflies that is popular among educators, scientists, and the public alike, Susan believes that she and her fellow researchers are ideally positioned to inspire a wide spectrum of audiences to become involved. Ultimately, this will serve to bring attention to the unusual diversity of insects – and insect behavior – to be found in the vanishing rainforests of Central and South America.

Read the full text of Susan’s paper, The Benefit of Being a Social Butterfly: Communal Roosting Deters Predation to learn more about the challenges Susan and her team faced, details about her experiment, and the implications behind her findings.


Each butterfly is marked with a number. Photo: Susan Finkbeiner

Changing Planet