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Date: Tue, 30 Jul 1996 00:24:27 -0400
From: Judy Johnson <jjohnson@asrr.arsusda.gov>
Subject: Moth Scales

Will the wing scales of moths or butterflies poison or blind you? Certainly not any that I am aware of, although its a big world out there and there are a whole lot of these wee beasties.

The scales of moths and butterflies are simply outgrowths of their exoskeleton, and thus are composed primarily of chitin. Being loosely attached, they rub off quite easily. As with just about any fine dust, it can be a potent allergen, and can be very irritating if it gets into your eyes. Research entomologists who must rear economically important pest moths must be careful to limit their exposure to these scales. The development of severe allergies in response to moth scales is a definite occupational hazard. I write here from personal experience and also refer to the following articles:

Wirtz, 1980. Occupational allergies to arthropods-documentation and prevention. Bulletin of the Entomological Society of America, 26: 356-360

Brenner, et al. 1991. Modernized society and allergies to arthropods. Bull. Ent. Soc. Am. 37: 143-158

These fragile little insects don't have a lot of physical armament with which to protect themselves, consequently they have become adept at camouflage, misdirection, and chemical warfare. A number of butterflies are known to accumulate noxious compounds from their food plants, using them to discourage predators. These chemicals either leave a bad taste, or will actually make the predator ill. One of the best-known examples is the monarch butterfly, which feeds as a caterpillar on milkweed plants. The cardenolides that the larva accumulates later protects it as an adult. Most birds that eat a single monarch become ill, and never eat another monarch, nor any butterfly that resembles a monarch.

I've not been able to find any indication that toxic compounds are specifically accumulated in the scales. Some butterflies have scales associated with glands on their wings that give off odors. These may behave as a sex attractant, or serve to repell predators. Some butterflies have abdominal glands that give off an exudate that is highly repugnant and can cause human eyes to water. A good reference on this is:

Brower, 1984. Chemical Defence in Butterflies in "The Biology of Butterflies" Princeton Univ Press (ISBN 0-691-08499-8).

The larvae of various moths are known for their urticating hairs, which can deliver a painful stinging sensation to human skin. These hairs may be a mechanical irritant, or may be associated with a toxin. I have particularly unpleasant memories associated with working with the grapeleaf skeletonizer (Harrisina brillians) due to their painful, nettle-like hair. It may be that some adult moths have a similar mechanism, but I don't know of any.

So, while I don't recommend snorting moth or butterfly scales, they are not poisonous.

Judy "Indianmeal moths make me sneeze" Johnson