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Nature Notebook – Milkweed Tussock Moth

What looked like tiny pieces of a black and white shag rug covered the Butterfly House door. The caterpillars of a milkweed tussock moth had just finished another molt and were in search of more milkweed.

They started their lives as a large family unit feeding together on the tender parts of milkweed leaves, carefully avoiding the veins filled with sticky latex sap. After the caterpillars developed their distinctive black tufts of hair, they were large enough to need their own space for eating so they spread out. After a few more molts they will enter pupation until next spring.

Like monarch butterflies, milkweed tussock moth caterpillars and adults can store the cardiac glycosides from the milkweed sap in their bodies. However, the adult moths do not have the typical warning color pattern because they fly at night. Nocturnal predators do not recognize colors.

Instead, the moths have an organ that emits an ultrasonic sound that bats (their primary predator) can easily hear. If a bat ignores the warning signal and tries to eat a moth, it will regret its decision. The noxious taste that accompanies the sound teaches bats to avoid the moths.