The Color of Poison

The Color of Poison – Moths by Kent McFarland

Scientists have catalogued about 160,000 moths around the world. There may be another 200,000 species yet to be discovered and described. In the United States alone there are over 11,000 moth species. Most of us think of moths as just drab brown, gray or white creatures of the night, but many are dressed as flashy as their butterfly cousins and can be seen flying in bright daylight.

Rattle Box Moths

Rattle Box Moth © Kent McFarland

One of the most striking diurnal moths is the beautiful Rattlebox Moth (Utetheisa ornatrix). It’s the only moth in eastern North America with pink-orange colored forewing marked with rows of white-ringed black spots. There’s good reason for the bright colors; they’re a warning. This moth tastes terrible. Their caterpillars dine on the leaves of Rattlebox (Crotalaria mucronata), which contain powerful alkaloids that the moths can store making themselves quite distasteful and unpalatable.

Predators don’t always heed to colorful warnings. These alkaloids don’t smell. For a predator like a spider, they have to taste it. But a mere taste from a spider could be fatal. The moths combat this with a volatile frothy blend of chemicals emitted from special ducts in their thorax. Disturb an adult moth and the bubbling brew is quickly exuded.

Scientists from Cornell University found during their research that even the moth’s eggs are protected from predators by these chemicals. Ants won’t touch them. Lacewing larvae stay back. Even parasitoid wasps won’t attack the eggs. But how are they protected before they are able to hatch and eat Rattlebox plants?

Incredibly, both the male and the female contribute nasty alkaloids to the eggs. The females transfer some that they sequestered as larva. The male contributes the fowl chemistry to the eggs when he mates with the female. He transfers a package that contains not only sperm, but also a pile of alkaloids that the female can quickly assimilate into her body and eventually to the eggs.

Mating lasts a long time; up to 9 hours. Just one mating will protect a female for the rest of her 30-day life. But that apparently isn’t enough. She’ll mate with up to 20 different males. How do the scientists know how many times a female mated? Each time a male passes a spermatophore to a female it is dissolved by the female and leaves behind a tiny hard ring. When the female dies, through dissection they can count the rings in her storage pouch. Each donut shaped ring represents a mating.

During this first ever National Moth Week, take time to enjoy and celebrate the wild colors of moths, just don’t taste them.

Kent McFarland (New England)

Tags: , , , , ,

One Response to “The Color of Poison”

  1. Hillel Brandes says:

    Amazing evolutionary “strategy”! Thanks!