Steven E. F. Brown

One of the many plants growing in our terrariums is milkweed, on which (among other things) Monarch butterfly caterpillars feed. Creatures that live and feed on milkweed tend to be brightly colored, as they take up toxic compounds called cardenolides while eating the plant, and those compounds make them bad-tasting and poisonous to predators. That’s why Monarch caterpillars and adult Monarch butterflies are so brightly colored.

Other insects, such as the Milkweed Bug, Lygaeus kalmii, are also brightly colored because they feed on the milkweed plant.

Our milkweed, besides being a host for Monarchs and Milkweed Bugs, is a home to hundreds of bright orange Oleander Aphids (Aphis nerii). They’re fascinating creatures, all female “superclones,” who apparently don’t need males at all, as male aphids of this species don’t exist in the wild, and can only be created by artificial conditions in a laboratory, as was done in Kyoto not long ago.

Our aphids do a strange, wiggling dance where they circle their abdomens, sometimes in synch with each other. No one’s sure why aphids dance like this, but one theory is that they do it to fend off tiny parasitic wasps. The wasp, Lysiphlebus testaceipes, lays its eggs in an aphid and the wasp larva kills the aphid, which turns dark brown, becoming a “mummy.” The baby wasp lives safely inside the husk of the dead aphid until it is ready to emerge as an adult imago. That exit from the husk is not always successful, as we found when studying our mummies under a microscope — one emerging wasp got tangled up during exit and died.

A crowd of Oleander Aphids (Aphis nerii) on a milkweed stem.

Milkweed bugs (Lygaeus kalmii) are also bright colored due to their toxicity. Note Aphis nerii on the same plant.

A “mummy” of a dead aphid, caused by the larva of a tiny, parasitic wasp.

Another aphid “mummy.”

The tiny wasp, Lysiphlebus testaceipes, doesn’t always make a successful exit from an aphid mummy. This one got tangled up during emergence and died.