Orange-something Spiny Oakworm

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Filed under Outdoor Notes

July 27, 2011

Orange-striped Spiny Oakworm moth

Orange-striped Spiny Oakworm moth

This is a common moth that is better known as a caterpillar. It is variably referred to as the Orange-striped Spiny Oakworm Moth and the Orange-tipped Oakworm Moth. In this instance, the scientific name is actually useful—Anisota senatoria.

I don’t know what Anisota means. As to senatoria, well, I’m not sure, but the caterpillars are greedy pests, so it seems appropriate.

Now, the scientific name is only useful if I have it right. There are several different species of Anisota, very similar in appearance, and I would not stake the farm on exactly which one or ones these photos represent—at least not the adults. This is an extremely variable species, and the males, which are smaller than the females, differ from the females, being darker with a translucent patch on each wing.

Orange-striped Spiny Oakworm

Orange-striped Spiny Oakworm

The caterpillars are a different matter. This is, indeed, an Orange-striped Spiny Oakworm. Note the orange stripes, the spines, and the oak leaves on which it is feeding

The moths tend to emerge in late June and into July. They are attracted to porch lights. In fact, most years they mate on my front porch.

Anisota senatoria mating

Mating moths, Anisota senatoria

The females will lay dozens of shiny egg-yolk yellow eggs on the underside of an oak leaf. The caterpillars will emerge and feed well into the late summer. They will spend the winter as pupae in the soil.

Anisota senatoria, female with eggs

Female with eggs

Spiny oakworm caterpillars can be extremely numerous; enough of them get smashed crossing our woods roads that the pavement can actually become a little bit slippery—a major eeew factor, if not exactly dangerous.

Orange-striped Spiny Oakworm

Orange-striped Spiny Oakworm

I suppose the orange stripes carry a strong “if you eat me I will make you puke” message, for the caterpillars seem generally to be left alone by insectivorous predators. Perhaps they have built up enough oak tannins to make them unpalatable. For those of you, like me, who played at “living off the land” as a youngster, you remember just how vile a raw acorn tastes. Now I never ate an oak leaf, but I suspect the effect of the tannin would be similar.

I have heard different evaluations of how much damage oakworms actually do. While they will certainly strip an oak tree, which appears very damaging indeed, some foresters whom I have consulted feel that that by the time the caterpillars peak, the trees have already stored their food, and consequently, this late defoliation does little real harm beyond the cosmetic.

On the other hand, folks who sell pesticides describe them in terms normally reserved for Biblical plagues.

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