Sunday, June 8, 2014

Hackberry Emperor

Hackberry emperor- Chris Barnhart
We recently have started seeing hackberry emperor butterflies, Asterocampa celtis.  Their identifying  eye spots, similar to many other butterfly species, can only be seen when they land.  These are a medium sized butterfly, brown and rather plain in flight, usually flying high in the trees but they often also fly rapidly around us as we walk through the trees. 

A special trait of this emperor is their attraction to humans.  They will frequently circle us while walking along the road or in the woods, looking for the perfect place to land.  If you watch carefully you can see them unfurl their rolled up proboscis and gently slurp up any sweat and salt off your skin.  This is harmless enough unless it lands on an insect-adverse individual in which case they occasionally get swatted.

Hackberry emperor larva - Chris Barnhart
As you might have guessed, their larvae feed on hackberry trees and are frequently seen on the underside of leaves during the night to escape predators.  They are ravenous eaters and can defoliate an isolated tree.  In the wild Ozarks, where they have so many hackberry trees to choose from, their larvae can be hard to find.  They have two generations a year and the fall variety wraps the leaf around its body and survives over winter as a larva (caterpillar), turning brown only to return to green the next spring to reach the final instar and pupate.*

Hackberry emperor -
Wikipedia says "The adults do not visit flowers, but feed on rotting fruit, tree sap, dung, and animal carcasses."  I don't intend to speculate on the relationship of dead animal carcasses and dung to their attractions to my sweat but will allow you to reach your own private conclusions.

Since they are cold-blooded like all insects, they can't control their internal temperature.  They can use shelter, sun exposure and other tactics.  By aligning their bodies perpendicular to the sun, they can catch more warming rays like we might by getting out into the sun on a cold day. 

When cold, they slow down and hide.  We use this trait to move, transport and even photograph captured butterflies in a chilled state.  They survive for several days in the refrigerator, awaiting the relative safety of the enclosed butterfly house.  By transporting them in a cooler, we prevent them from dehydrating or damaging their wings by flapping to escape.  When released they need to warm up their flight muscles and like some other species they "shiver" before flying off.  You can watch this just before they flutter out of their ziplock bags, into the safety of the Butterfly House.

* University of Milwaukee Field Station

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