Tuesday, August 31, 2010

Giant Swallowtail Larva

Some people find it hard to believe that a face like this can be found on an animal in Ohio. It looks to me like something you would see on the Outer Limits. This is the front end of a Giant Swallowtail Larva and the face is just a decoration that’s part of its defensive arsenal. The actual head is located below that mouth-like slit.

Earlier this year I showed the young larvae that depended on their resemblance to bird droppings to avoid being eaten. Larger specimens still bear a bird dropping appearance, but they are much more noticeable and have gained a few additional tricks to avoid being something’s meal. At the slightest disturbance, the enlarged thoracic region of the caterpillar raises to display its mask to a potential predator. A show of eyespots is often an effective way to scare off birds.

A more aggressive disturbance causes the caterpillar to draw its weapon, a projectable organ known as an osmeterium. The osmeterium exudes an unappealing substance that combines touch and smell to deter predators. In cases like this, I usually attack using a stick so as to avoid carrying the odor with me on my fingers.

If the attacker comes from the front, the osmeterium takes on the appearance of a snake’s tongue, another visual deterrent to attack by birds.

This larva is about an inch and a half long. It won’t be long before it moves off to find a suitable place to form a chrysalis, the form in which it will spend the winter. Maybe I’ll see this guy in adult form next spring.

I found several suitable photographic subjects. There are many fluorescent blue spots and streaks that make the caterpillar appear to be throwing electrical sparks. I wonder if those might serve as another warning to potential predators.

A single clump of Prickly Ash contained half a dozen larvae. Most were resting quietly on the stems, but this one was busily consuming a last leaflet.

There’s quite a defoliation effort going on here. Fortunately, there are only one or two larvae per shrub. If these can all make it through the winter, next year may surpass our current record butterfly numbers.


  1. That is to wild Steve..How could such a beauty of a butterfly look so ugly at this stage!!
    That is real interesting how it protects it self with it defensive disguise!!
    I would stay away about the time it looks like a snake head!! ; }

  2. I hope the picture of the fake snake's tongue didn't scare you grammie g. I figured that since you already knew it was a caterpillar, you could survive the shock.