Edwards' Hairstreak Larva at Night

I went out Memorial Day evening to witness the Edwards’ Hairstreak butterfly larvae exiting their daytime underground shelter and climbing the tree for a night of oak leaf consumption.  This is a behavior exhibited by only the more developed larvae and it is an event that I have always managed to miss.  I think I nearly missed it again this year.  I did see some larvae, but several trees that showed signs of heavy feeding were free of larvae.  Adult butterflies begin emerging in early June, so it’s likely that many of the larvae have already pupated.

I arrived at my target tree at 8:45, just as a Whip-poor-will began its song.  After checking the tree and finding no larva movement, I set up my lawn chair and got ready for a wait.  Despite a temperature of 84 degrees, I put on my jacket and hood to keep off the swarm of mosquitoes.  At 8:48 I again checked the base of the tree and witnessed the emergence of the first larva.  I guess I did a pretty good job of guessing when activity would start.  At 9:03 a Chuck-will’s-widow began calling in the valley below the ant ridge.

A four battery Mag-Lite was my source of light, but the camera flash illuminated all of my photos.  The flash light beam caused the larva to stop its progress and seek cover, so I used it as sparingly as possible.  As the larva began its journey up the tree, there was still enough natural light to find my subject through the view finder.  The larva had to endure only random flashes which I thought wouldn’t be too much different from what would be experienced as a result of an electrical storm.  For serious behavioral observations I’ll have to have a light that doesn’t change the larva’s behavior.

The larva spent about six minutes traveling three feet up to its feeding position.  While the larva was traveling, the Chuck-will’s-widow moved into a cluster of small trees about 50 feet from my position.  After about a minute of making its typical call, it began producing a low rhythmic call that sounded like a soft Bong-Bong-Bong note produced through a Didgeridoo accompanied by the sound of clapping wings.  Chucks have just become common in this area during the last few years and I thoroughly enjoyed this opportunity to experience this aspect of its courtship display.

There was always one ant with the larva.  This one is receiving its motivation for attending the larva, a taste of honeydew.  I’ve read several accounts that describe the ants herding or driving the larvae as they journey up and down the tree.  I never witnessed any indication that the ants had any control over the actions of the larvae. The ants remained in the company of the larvae, but the larvae seemed to control their own actions.  The ant behavior reminded me more of children following after the ice cream truck.

Once on the leaf, the larva ate continuously.  The mouth was never visible from above and except for subtle shifts in position, no movement could be observed.  I headed back to the house after a couple hours of observation.  I was really happy to finally see this phase of the Edwards’ Hairstreak life cycle.  If I can manage to witness adults depositing eggs on the oak, I’ll have captured the entire life cycle.  Maybe I can manage that next month.