Yellow aphid with black stripes on wings
We were sitting at our picnic table in the yard on September 3, 2012 when this little yellow aphid landed on Sandy. Its body was about the length of this underscore ( _ ) if you are reading this in standard 12-point type .
While there are a lot of different kinds of aphids, there are only a few that are yellow, which narrowed things down significantly.
The other key ID features that really narrowed things down were the mostly-black legs, and the black stripes running from the head all the way back along the edge of the wings.
This looks like one of the aphids in the subgenus Lineomyzocallis. These are a small group of very similar aphid species in the genus Myzocallis that feed on oak trees, which we have in some abundance. They aren’t particularly well-studied, because they don’t appear to cause much harm to the oak trees they infest.
At first I thought it was one of the much-better-known Oleander Aphids, Aphis nerii, which are widespread and feed on milkweed plants. But the Oleander Aphids don’t have that prominent pair of black stripes running down the back. The only real similarity is the canary-yellow color. In the case of the Oleander Aphids, the color is a warning that the aphids are chock-full of the toxins they accumulate from the milkweed they feed on. It is possible that the color of the Lineomyzocallis aphids is also a warning color, as oak trees are loaded with tannins and the aphids may well be accumulating them as a chemical defense. While tannins aren’t as noxious as the glycosides that insects can acquire from milkweed, they taste horrible enough.
 I really should have put on the close-focus lens for this little guy, the pictures came out a bit blurrier than I would have liked.
 Tannins are the reason why people don’t just casually snack on acorns. Bitter, bitter. While you can make food out of acorns, you have to spend some time leaching out the tannins to make them passably edible. Squirrels evidently can’t taste tannins (or maybe even like the flavor). Lucky, lucky squirrels.