The kissing bug, illustrated for an article on Chagas disease for Consumer Health Interactive.
The peppered moth, one of the first examples of natural selection observed in real-time. The predominant coloration of the moth population went from light to dark as soot from coal burning factories coated the white bark of trees and changed what worked as camouflage. Lighter colored moths were selected again when the pollution was brought under control.
The potato bug, which coats its larvae with feces as a form of defense. For Everybody Poops 410 Pounds a Year, from Ulysses Press.