the extraordinary harvester

The Harvester (Feniseca tarquinius) is a handsome small butterfly, but not outstanding; it is easily confused with other orangey species such as coppers or skippers. But this unassuming insect, no larger than a man’s thumbnail, is unique in North American lepidoptera. The life cycle of the Harvester is tied to that of woolly aphids, and is a fascinating lesson in ecological interplay and interdependence.

Every schoolchild learns that butterflies lay eggs on plants, the caterpillars feed on the vegetation, grow, form a pupa, and eventually emerge as an adult butterfly which will probably feed on flower nectar, but may instead feed on rotting fruit, sap, or some other organic matter. The Harvester does something different just about every step of the way, breaking all the rules.

Female Harvesters lay their eggs among woolly aphids (Neoprociphilus, Pemphigus, Prociphilus, and Schizoneura). These insects are interesting in their own right. They have both winged and wingless generations, nearly all of which are female, and they usually require at least two different hosts. For instance, the woolly alder aphid (Paraprociphilus tesselatus), a species in which Harvesters are frequently associated with, requires both alders and silver maples, with different generations feeding on each tree. Lucky for me, the woodland where I work has both tree species in abundance.

Woolly aphids, like other aphids, feed on plant juices and subsequently exude undigestible plant sugars as a sweet substance referred to as "honeydew." This honeydew attracts ants, which will carefully tend and protect aphids in order to exploit this handy source of nutrition. There are any number of species of aphids and ants that have this type of mutualistic relationship. Enter lepidoptera: some ant species have the same type of relationship with larvae of the butterfly family Lycaenidae, nearly all of which also produce honeydew and thus prompt the same interest and devotion from ants.

Harvesters are also members of the Lycaenidae (the plot thickens), but the dietary habits of their larva turn the typical ant/caterpillar alliance on its ear. When Harvester larvea hatch, they eat the woolly aphids – they are the only carnivorous butterfly larvae in North America. Aphid-munching puts Harvesters a bit at odds with the ants, and so the larva will sometimes conceal and protect themselves under a mat they spin from silk and festoon with aphid carcasses. Recent research has also found that Harvester larvea can produce a chemical camouflage that mimics the species of aphid on which they are feeding. These larvae are therefore undetectable to the ants, and are spared the ant-rendered molestation which invariably befalls other aphid marauders.

Harvester larvae pupate into chrysalids that are said to bear resemblance to a monkey’s face. I sort of think they look more like dog faces, but then again, some people see faces in tortillas, ceiling tiles, and grilled cheese sandwiches, so who am I to assess these effigies?

Adult Harvesters are no less dependent on woolly aphids – they also feed on aphid honeydew. A Harvester butterfly possesses a proboscis that is too short to be of any use in sipping nectar, but is well adapted to imbibing on honeydew.

Harvesters, then, which are endemic to eastern North America and the only representative of the subfamily Miletinae in the New World, are never far from the suite of tree species which host woolly aphids. Because not all host trees will be infested with aphids, Harvester populations can be quite ephemeral. Even though all the elements were in place here in my local patch, I have looked for this remarkable butterfly without success for over ten years. I feel quite satisfied to have finally been rewarded with a first-hand glimpse at its intriguing life.

Comments

[Mark O'Brien]

Excellent write-up. I have already told Phil Myers he should pay you to do this for the Animal Diversity Web project... :)

[Madison]

I think i found a Harvester caterpillar. Mine eats aphids, but instead theyre oleander aphids found on a tropical milkweed.