Bedbug sex is rough, to say the least. Males jab females in the abdomen with a spur structure to inject sperm, spilling her blood and guts in the process. Instead of evolving weapons of resistance, flexible underbelly armor allows females to tolerate the encounter, a team of researchers report February 11 in Proceedings of the Royal Society B.
Looking at female beg bugs (Cimex lectularius) under different microscopes, scientists found that the exoskeleton area where the males notch their spur is full of stretchy proteins called resilins. Piercing the exoskeleton there requires less force and produces less carnage than elsewhere on the female's body.
This can’t be interpreted as female choice by any means, but the researchers suggest that tolerance played a key role in the evolution of violent bedbug sex habits.