(Euchaetes Egle, Milkweed Tussock Moth)
The funny thing about nature is…the more you know, the more you understand how little you know.
What you might know:
Many butterflies rely on specific “host” plants to lay their eggs. Monarch butterflies, for instance, require milkweed plants as their host plant. Milkweed gets its name from the milky substance inside its stem and leaves that contain toxic chemicals. Those chemicals don’t hurt the monarch caterpillars, but they will hurt anything that eats them as larva or in their final adult butterfly forms. For instance: a bird will stumble on a monarch caterpillar or butterfly and decide to eat it despite its bright “warning” colors. The bird will get a very upset stomach, throw up, and learn to associate the colors of the monarch with an upset stomach, dissuading them from eating them again in the future.
(Danaus plexippus, Monarch Butterfly)
What you might not know:
Common Milkweed is also host plant to the milkweed tussock (or tiger) moth caterpillar (Euchaetes Egle). The chemicals inside of the milkweed plant protect this moth in almost the same way that it protects the butterflies. The difference is found in the dark…
Since tussock moth caterpillar is bright and showy, it is pretty easy for birds to pick out as a “don’t eat me” prey during the day. The Tussock moth, however, looks a whole lot like other ‘boring’ brown moths. So how do birds know not to eat it?
Well, they probably don’t.
It’s a moth, not a butterfly. Moths are active at night and so are their predators: bats. Bats don’t give a flap about the color of their food BUT they learn a different association (or dissuasion) for the toxins from the milkweed plants the tussock larva ate. The milkweed tussock moth evolved an organ that emits an ultrasonic signal easily detected by bats that is specific to them. The signal, and the association of that signal, warns bats that eating this moth will be rewarded with a noxious, vomit inducing meal.
Cool yeah? These guys will be in their larval stage at the end of August into early September and they’re known for living on the milkweed plants you can find at Latta Nature Preserve – come see them! In fact, if you want to be a hero to these little tigers and their endangered milkweed neighbors (the monarchs) plant some milkweed in your backyard!
Want to learn more about butterflies and their host plants? Check out this fantastic article from Birds&Bloom that explains common myths about butterflies and how to attract them to your yard.
Myths and Facts About Butterfly Host Plants - Birds and Blooms