Aphid in Sheep's Clothing

I will never grow up. I am still asking small-child questions: "What is this?" "What does it do?" "Why?"

The green bugs Laurie brought me the other day have been keeping me busy. Google was little help, this time; I had nothing to go on, other than "green bug, alder, cottonwood". I posted my photos, such as they were, on Bug Guide; the next morning, a commenter said they looked like "woolly aphids". Back to Google, to research woolly aphids on alder.
First, I discovered that woolly aphids produce their own "blanket"; it is not cottonwood fiber, even though it looks similar, and is also coating leaves in the vicinity. Instead, it is a waxy substance that they exude from the anus, as other aphids exude honeydew.

I compared a cottonwood twig, with seeds and fiber, with the fiber from the bugs. The cottonwood was not quite as white, silkier to the touch and more "feathery". Fiber from the suspected aphids was sticky; cottonwood fiber was sticky only when it had already come into contact with the leaves where the bugs were. So that checked out.

But then I ran into problems. The woolly alder aphid is common in BC, is covered with a white, sticky fibrous blanket, migrates from maple to alder in early summer, and eventually covers the leaves with a sticky nectar which leads to the growth of a blackish mold. Check, check, check, check and check. Except that all the photos of woolly alder aphids without the coating were nothing like mine. Wrong colour, wrong eyes, wrong shape.
A close-up of my bug, shorn of its "wool". Note the little wings or wing covers; he beat those winglets, but never managed to fly with them. Also note the absense of visible mouth parts or pincers. And the "goggles"; black circles around the eyes, as though written on with a felt pen. The tail is black, but in two sections, with the rear-ward one being slightly greyer. You can see where the wool is produced; a small bit still sticks there. (Ignore that red fiber: it's a piece of my carpet.)

I looked at hundreds of photos of woolly aphids, of all sorts; none of the denuded bugs were anything like mine.

Could something else mimic these? Something that, under the disguising blanket, turn out to be another beast? A predator? A "wolf in sheep's clothing," in miniature?

In the New Westminster Library, I searched the indexes of insect books for "woolly aphid". Mostly, it wasn't there, or referred to one or two lines of text. But there was a new (to the library; it's from 2003) book: For Love of Insects, by Thomas Eisner. And it has 20 pages on woolly aphids, a mimic, and its interactions with the aphids and the ants that "farm" them.

The green lacewing larvae prey on woolly aphids. Some of these are known as "trash bugs"; they purposefully coat themselves with bits of debris, including food leftovers. Eisner discovered some of these that took the waxy fibers from the woolly aphids, and covered themselves with them, until they could pass for a large aphid themselves.

He pulled the covering off some of these, the same way I had with my bugs, and watched. They immediately set about covering themselves again, grabbing pieces and twisting around to place them on their spiked backs until they were completely disguised again. (I went back and looked at the bugs I had stripped the day before; they were also back to normal, sheep ready for the shearing.)

Ants are well known for their talents as aphid farmers. They will stand guard over their herd of aphids, protecting them from wasps and other invaders, including humans, and "milking" the aphids for honeydew by stroking them with their antennae. The woolly aphids also produce this honeydew, along with the wool, and are shepherded by ants for this purpose.

The green lacewing larvae escape the notice of the ants by stealing the waxy fibers from the aphids they will be preying on. Eisner and his staff stripped the larvae and placed them back in the colony of aphids; ants attacked them right away. Some they killed outright, others they carried away and threw off the branch. A few were eaten. But an ant that bit a larva coated with fiber got a mouthful, and retreated to clean himself off. After a few attempts, they ignored the larvae.

So: were my bugs lacewings? If so, it was odd that I hadn't seen any lacewing eggs anywhere; these are noticeable, because they lay them one at a time on top of a 1/2 inch stalk. To me, they would look at first glance like one variety of slime mold, which I keep a lookout for.

And none of the lacewing larvae looked anything like my bugs, either.

Besides, all the lacewing larvae that I could find, and all the descriptions, mention the large mouthparts , the "powerful jaws" "like ice tongs". My bugs have no visible mouthparts at all, no matter what position I prodded them into. And smooth bodies, with no spikes.

So, what are they? I still don't know. For now, I'm going with "woolly aphid". But not the woolly alder aphid, nor either of the two invasive woolly aphids here in BC, the woolly balsam aphid and the woolly hemlock aphid.

A "normal", non-woolly aphid, on another leaf from the same tree, for comparison purposes.