Sunday, May 28, 2017

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.

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