Most caterpillars (butterfly larvae) are vegetarian: they eat plants of one species or another (each caterpillar species has its preferences)… but that’s not the case with the caterpillar of the harvester butterfly (Feniseca tarquinius). The caterpillar of this North American species is carnivorous: it consumes only insects, specifically woolly aphids, with a distinct preference for the woolly alder aphid (Prociphilus tessellatus).
The harvester is distributed throughout eastern North America as far north as Lake Saint-John in Quebec and as far west as eastern Manitoba. It can be seen all summer as there are several generations each year. It’s a small butterfly with only a 23 to 32 mm wingspan and a fast, erratic flight habit. It’s color is variable, but essentially orange with large dark brown patches and spots.
The adult butterfly itself doesn’t eat insects, but it does harvest the honeydew (sugary exudate) from the same aphids its larvae will later consume.
The carnivorous caterpillar is small and greenish gray, covered with fine white hairs. Like a wolf in sheep’s clothing, it often covers itself with the bodies of its victims. This helps it to better hide from its predators.
The chrysalid too is unique and looks like a tiny monkey head.
I think you’d have to agree that this butterfly is just a bit creepy!
A European Carnivorous Butterfly
There are no harvesters in Europe, but the Europeans, too, have a carnivorous butterfly. It’s the charmingly beautiful and quite rare great blue (Phengaris arion, formerly Maculinea arion)… and all I can say is that it’s even more sinister than the harvester!
At first, its caterpillar eats leaves like most caterpillars do, living on thyme and oregano, but can’t complete its life cycle on plants alone. That’s when its darker side comes out.
Its shape and behavior mimic that of the larva of a species of ant that mistakenly picks it up and brings it back to its nest. Once inside, the caterpillar survives… by eating the larva of its host.
Now that’s creepy!