Eye-shaped markings at the edges of butterfly wings stop predators from striking vital body parts.
Kathleen Prudic, now at Oregon State University in Corvallis, and her team let praying mantids (Tenodera sinensis) feed on Bicyclus anynana butterflies, which have small, drab eyespots in the dry season and larger, brighter spots in the wet season.
The mantids more readily detected wet-season butterflies than dry-season ones, but were less successful at capturing them because they tended to attack the wings rather than the body. Butterflies with wet-season wings lived longer and laid more eggs in the presence of mantids than did their dry-season fellows.
Even dry-season butterflies with large bright spots pasted on their wings showed these fitness benefits.