More urban species: Hallowe'en aphids

Some zookeepers were passing through one of their exhibit gates only to discover their skin and clothes stained by some purple substance. There were also a lot of flies and yellow jackets flying around. Finally someone noticed the aphids.


A lot of aphids. The purple staining came from the crushed bodies of hundreds of aphids. Since aphids normally spend nearly their whole lives on their host plant, this behavior is a little strange. My best guess is that they overpopulated their host plant and dispersed out of necessity. Above this gate is one of many Austrees in a row. An Austree is a ornamental willow hybrid developed for use as a windbreak--it grows straight and very fast. Researching willow aphids, I found that they feed on second year growth; there would only be so much of this kind of growth on each tree.


Most aphids are wingless, but some are born with wings, allowing them to fly to new host plants to establish new colonies.

Aphids famously produce a waste material called honeydew, which other insects use as a food source. Ants are usually the ones you think of accompanying aphids, but in my experience yellow jackets are drawn to aphids in the fall, when the yellow jackets are desperate for a source of liquid food. (Yellow jacket adults can't feed on solid food, so they feed their larvae solid food and the larvae regurgitate a liquid the adults can eat. In the fall, the queen stops producing new larvae and the workers must find liquid sugar on their own, thus the misery they cause to late summer soda drinkers and ice cream eaters.)

Looking on bugguide, it's clear that these are genus Pterocomma, large aphids that feed on willow or poplar. They most closely resemble, in appearance and behavior, other aphids on bugguide not identified to species, but named "halloween aphids" by one user. Their coloration plus their sudden appearance in October justifies this common name to me. I hope some aphid expert identifies them to species (and keeps the name "halloween aphid.")