Nature Commun. doi:10.1038/ncomms1002 (2010)

Credit: J. YACK

Animal displays are thought to evolve from ancestral behaviours that turn, over time, into ritual communication signals.

The masked-birch caterpillar (Drepana arcuata Walker, pictured) conveys ownership of its territory with vibrations, including the dragging of its anal segment across a leaf to make a scratching noise. The behaviour typically staves off intruder caterpillars. Jayne Yack of Carleton University in Ottawa, Canada, and her colleagues have found that the anal scraping seems to be a modified component of a typical territorial behaviour observed in a number of related, ancestral species — an aggressive crawl towards intruders.

Body movements previously associated with fighting can become ritualized, the authors suggest, permitting conflict resolution without physical altercation.