Nature at its Best: Edwards' Hairstreak Butterfly

Edwards' Hairstreak, Satyrium edwardsii, is a beautiful little butterfly with a fascinating life cycle. It is called a hairstreak because of the hair-like projections found on the back of the hindwing. It is believed the "hairs" look like antennae and will fool a predator into biting them, thinking it is the head. The butterfly can then escape with only a little damage to the wing. A rarity for Indiana, this butterfly is found in only a few counties near Indianapolis-Brown, Tipton and Parke. But, most records are found in Northern Indiana. Check out the map for all the counties in Indiana where it is found.

Edwards' Hairstreaks are found in dry thickets and woods where there are oak trees. Eggs are laid in crevices and wounds in the bark. The young caterpillars feed on oak leaves during the day, older larvae feed only at night.

And this is where the story becomes interesting. The butterfly has a symbiotic relationship with a species of ants called Allegheny Mound Builders, Formica exsectoides. These ants build huge mounds that can reach two to three feet in height and four or five feet in width. The ants are always busy collecting food and protecting their mound. I observed many ants carrying dead insect and spiders to the mound. Below is a mound of the Allegheny Mound Builders.

The ants also rely on the caterpillars for a food source. The caterpillars produce a sugary secretion called honeydew. The ants will carry the older caterpillars down into the mounds at the base of the oak trees. The moundbuilders will "milk" the caterpillars of the honeydew and in return protect them while they are feeding in the trees and keep them safe in the mounds. Later, the caterpillars will pupate inside the mounds.

Above is a photo of the Allegheny Mound Builders. What an amazing relationship between these two species!