Hagenius brevistylus (Gomphidae) was shown to prey on an aposematic model, the monarch (Danaus plexippus) when the butterfly’s densities were high. The mode of prey capture and feeding, where the butterfly’s thorax and abdomen are eaten first, avoids the highest concentrations of cardenolide poisons stored in the wings and exoskeleton. The feeding mode is virtually identical to that of the known vertebrate predators of Danaus.