Tuesday, August 16, 2011

Wooly Alder Aphid

I have a patch of Common Alder shrubs upon which the Wooly Alder Aphids seasonally appear. I check the aphid colonies every summer in hopes of finding Harvester butterflies whose larvae feed upon the aphids. So far, I’ve not found any of the butterflies, but I always enjoy watching the aphids.

Wooly Alder Aphids overwinter as eggs on Silver Maples and begin their colonies there in the spring. The aphids mature into winged adults on the maples and then fly off to establish colonies on alders. By the end of summer the aphid colonies may contain hundreds of individuals. In the fall, mature aphids leave the alders and return to the Silver Maples to lay eggs.

Wooly Aphids produce long waxy strands that resemble silky hairs. As the aphids grow and molt, the shed skins clump together into brown masses.

Like other aphid species, Wooly Aphids secrete a sweet liquid known as honeydew. The honeydew accumulates on leaves and branches below the aphid colony Sooty mold often grows on the honeydew and forms a thick, black covering.

Many species of insects visit the aphid colonies to collect the sweet honeydew. This is the Four-toothed Mason Wasp, Monobia quadridens, a black and white wasp which commonly feeds on nectar. It is a predator on caterpillars which it seals into nest chambers to feed developing larvae. I’ve never seen these wasps act aggressively, but they are often swatted because people mistake them for a Bald-faced Hornet.

Flies are always attracted to sugar water, so the honeydew covered leaves bring in a number of different fly species. I do find it odd that I never find any ants near the Wooly Aphids. Every other honeydew producing insect at Blue Jay Barrens is accompanied by ants, but not Wooly Aphids.

There are about a dozen Common Alders growing in this corner of an old crop field. They were planted here 25 years ago. I keep hoping that a Harvester butterfly will find them and their aphids. I’ll keep looking.


  1. I also really want to see a Harvester caterpillar! It is on my bucket list. :)

  2. I'm also always checking out aphid colonies like these looking for Harvester caterpillars. I once spotted an adult Harvester butterfly in the area, but have yet to find a caterpillar.

  3. Hi, Janet. Finding a Harvester caterpillar would certainly be exciting. I've not given up hope.

    Hi, Troy. If I found an adult Harvester, I think I would have to start checking the aphids one-by-one to make sure I wasn't missing any caterpillars.

  4. I saw something similar on stalks of coneflower earlier this summer; only 3 individuals. I will have to check again to see if they are still there. There are no alder shrubs nearby that i am aware of. Are there other plants they frequent?

  5. Hi, Wilma. There are several species of wooly aphids, so it's possible to find them on a variety of plants. There are also some plant hopper larvae and scale insects that produce a fuzzy covering, so it could be something like that.