Hackberry Emperor

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Filed under Outdoor Notes

June 14, 2011

There was a huge Hackberry tree (Celtis occidentalis) where I grew up. It had uneven leaves, knobbly warty bark, little hard berries, and usually some galls on the leaves. I am familiar with the tree, but although range maps indicate that this is on the border of their range, I have never seen one up here in the mountains.

So, I was a bit more than a little surprised the other day to see several Hackberry Emperor butterflies (Asterocampa celtis) fluttering around in a State Gamelands parking lot.

Hackberry Emperor (Asterocampa celtis)

Hackberry Emperor

Hackberry Emperors, as the name implies, have a pretty tight relationship to Hackberry trees. They are Hackberry obligates, which means that the butterfly can only live near the tree (in this instance, it is the only food the caterpillars will eat). Therefore, the presence of several nice fresh Hackberry Emperors flying around the parking lot means that there must be a Hackberry somewhere nearby.

So I looked around a bit, and sonofagun, there they were, several small trees growing along the edge of the parking lot.

Hackberry leaves

These are elm leaves, not Hackberry leaves--thanks to Chuck Kiewegfor setting me straight.

If you look closely at the top of the leaf, you can see that it comes out flat on one side and more rounded on the other.

That, along with the pointy tip and the saw-toothed edge is fairly diagnostic. Note also that someone has been chewing on this leaf. Wonder who. There are, in fact, three different species of butterflies that are Hackberry obligates: the Hackberry Emperor, the Tawny Emperor (Asterocampa clyton), and the Snout Butterfly (Libytheana carinenta).

Until this week, I have never seen any of these in Pennsylvania. I suspect I will be hanging around that parking lot quite a bit over the next few weeks.

I think that one of the reasons–beyond the “little boy” urge–for collecting insects, and particularly butterflies and moths, is that they are exquisitely beautiful when viewed close up. The underwing of the Hackberry Emperor is certainly a fine example.

Hackberry Emperor butterfly underwing

Hackberry Emperor underwing

Beyond the striking black and white pattern of the forewing (and those nifty white antenna tips), Hackberry Emperors are not the flashiest of butterflies; in fact, in flight, the general impression is of a deranged brown moth zipping around some sunlit open space. They are one of many species whose eye-catching upper wing surfaces sharply differ from a cryptic–and often beautifully detailed–under wing surface.

The Kaufman Field Guide to Insects discusses this cryptic versus flashy phenomenon in Catocala moths. ”If they are disturbed into taking flight, the contrasting patterns of their hindwings will flash out, a striking effect that may startle predators and allow the moths to get away.”

Well, maybe so; I’m sure those folks are smarter than I am, but it doesn’t compute for butterflies that spend many daylight hours fluttering around and showing off those flashy colors.

I have a different theory for day fliers–the “flash and hide strategy.” Consider a predator that is pursuing a brightly marked flying insect when, suddenly, that insect lands and becomes pretty much invisible. Now, it doesn’t take a lot of focus on the part of a pursuer to track a brightly colored moving target, but to switch its acquisition picture–while in pursuit–to searching out a cryptically colored stationary target is probably close to impossible.

“Flash and hide” works pretty well at fooling humans too, if you’re not ready for it.

Look for Emperors in the afternoon when the sun is out, they don’t seem to like it overcast. Apparently they seldom visit flowers, but they do spend a lot of time probing the ground for minerals. They are also famous for landing on naturalists to drink perspiration.

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