Edwards' Hairstsreak Larvae - Night Feeding

Within the Blue Jay Barrens prairie openings are a scattering of medium to small sized Blackjack Oaks.  Some of these trees are decades old, but various environmental factors keep them from getting very large.  Dry site conditions limit water available to the tree, White-tail Deer find them to be the perfect choice for rubbing antlers, Periodical Cicadas cause a dramatic die-back every 17 years and a wide variety of insects find the leaves extremely palatable.  I make several close examinations of these trees each spring as I follow the development of the Edwards’ Hairstreak butterfly larvae, one of those species with a dietary preference for Blackjack Oak.

Edwards’ Hairstreak eggs hatch just as the oak buds begin to swell in early spring.  The larvae feed on the buds and newly developing leaves.  On May 8, temperatures dropped to 29°F causing frost and freeze damage to many plants.  Damage to Blackjack Oaks varied between individual trees, but all suffered the loss of some new growth.  This was a setback for both the trees and the Edwards’ Hairstreak larvae.  Fortunately, buds were not affected and regrowth was rapid.

When I checked the Blackjack Oaks three days ago, the leaves were showing signs of heavy predation by the Edwards’ Hairstreak larvae.  When this magnitude of damage occurs to the leaves it is a good indicator that the larvae have reached their final instar stage and will soon be pupating.  At this point it does no good to search the tree for larvae, because they do not spend the day in the open.

Young Edwards’ Hairstreak larvae remain in the open feeding through the day.  When they become older, they feed only at night and spend the day at the base of the oaks, hidden in cavities constructed by Allegheny Mound Ants. 

Near sundown, the larvae leave their shelter and begin climbing the tree.

Each larva is accompanied by its own cadre of ants. From the time they hatch until emergence as adults, the Edwards’ Hairstreaks are accompanied by ants.  The larvae achieve a degree of protection from the ants and the ants receive a sugary Honeydew solution excreted by the larvae.

The larvae on the first tree went too high to be easily observed, so I switched my attention to a smaller tree that displayed feeding activity.  This tree was less than three feet high and struggling to regrow leaves killed by the freeze.

The larva’s head is located near the top of this photo.  As the larva eats, an ant visits honeydew producing glands near the larva’s tail.

It’s fortunate that pupation is near.  This tree was loaded with larvae.  At the rate they’re eating, the tree may soon be stripped bare of leaves.

The above video is a compilation of several shots of moving and feeding Edwards' Hairstreak Larvae.  Make sure your sound is on, so you can enjoy the call of the Chuck-will's-widow while you watch.  This video, in a possibly clearer form, may also be viewed on YouTube by clicking HERE.

Edwards' Hairstreak Hatchlings

The eggs laid last summer by the Edwards’ Hairstreak butterflies have recently hatched and the buds of the Blackjack Oaks on the barrens are now full of Edwards’ Hairstreak larvae and their attendant Allegheny Mound Ants.

Most of the action takes place on these small Blackjack Oaks. The Edwards’ Hairstreak butterflies sometimes lay their eggs on the larger Oaks, but it’s much more likely that they will use an oak that is less than 6 feet tall.

In order to consume the sweet secretions, called honeydew, produced by Edwards' Hairstreak larvae, Allegheny Mound Ants stand guard and protect the larvae from predators.  The ants protect the larvae from hatching until emergence of the adult butterfly, even though the larvae only produce honeydew during the final few instars prior to pupation.  This type of behavior, where two different species interact to each species benefit, is called mutualism.  In the photo above, two larvae are located just to the left of the ant's head.

The larvae tend to begin feeding at the base of the bud. Leaves that unfurl in a couple of weeks will be laced with holes made by the larvae munching their way through the bud.

Blue Jay barrens has four different Prairie openings that contain quantities of young Blackjack Oaks. I found Edwards’ Hairstreak larvae on trees in all four areas. Some of the buds were really loaded down with larvae. There may not be anything left of these buds to produce leaves later on.

The key to finding the larvae is in finding the ants. If there are no ants on the tree, there are no larvae.  In a couple of cases, ants congregated to protect tree hopper larvae, which also form a type of honeydew. Even in these instances there were butterfly larvae feeding at the same location.

On occasion I would get a bit too close with the camera, causing an ant to take action against me. In each instance, I would direct the ant back onto its bud so it could continue with its duties.

I have been nurturing small Blackjack Oaks at Blue Jay Barrens in hopes of expanding the population size of the uncommon Edwards’ Hairstreak butterfly. I’ve been seeing signs of success during the past couple of years, but this year, the quantity of young larvae far exceeds anything I have seen in the past. The ants have always been present, and now the addition of more trees means more butterflies. The numbers of adult butterflies should be truly amazing this summer.

I’ve included a couple of short videos showing Allegheny mound ants interacting with the Edwards’ Hairstreak larvae. You can watch the above video on YouTube by clicking HERE, or the below video by clicking HERE.