Sandy spotted these on September 10. They were on a Tag Alder bush beside the trail going to the back of our property.

I recognize these, because I’ve posted about them before. They are Wooly[1] Alder Aphids, Prociphilus tessellatus. And, these particular aphids were being tended and closely guarded by some good-sized ants (which were after the honeydew that the aphids secrete):

I believe that the ants are carpenter ants, and they look a great deal like the New York Carpenter Ant, Camponotus novaeboracensis. They were very defensive of their aphid herd, and when the girls touched the aphids the ants would run out onto their hands to try and bite while spraying formic acid[2]. Sam and Rosie both thought this was pretty funny, because the ants couldn’t get a good enough grip on the skin of their hands to actually hurt, and the formic acid spray just made a sharp, sour odor rather than actually hurting anyone. Still, the ants would have done a real number on any predatory insects that might have approached their herd.

It was hard to see the aphids too clearly through the obscuring wax filaments that they make for protection. When Sam pulled some off the branch and held them in her hand, we were able to see that in addition to the wingless ones, there were a bunch of them with wings.

These are the sexual reproductives. Like other aphids, there are two forms: the wingless ones that reproduce parthenogenically (which are the ones that breed fast and rapidly build up the aphid mass), and the winged ones that come in both male and female (which are the ones that fly off to overwinter, and then in the spring start new aphid masses). These winged ones aren’t even present until the end of the summer, and they will be the only ones that will survive once it gets cold.

Woolly alder aphids usually just wither a few leaves on their hosts, and don’t normally do that much damage to the plants. And, their host species (mostly alders or silver maples) are not of great economic importance in any case. As a result, the main effect of having woolly alder aphids around is that they provide food for a lot of things that eat aphids (lacewings, lady beetles, hover flies, and parasitic wasps, among others). So they could actually be considered beneficial, because they support populations of aphid predators that will then help to keep the numbers of other aphid species down on your actual crops.

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[1] You know, I’m really not sure whether it is supposed to be spelled “woolly” or “wooly”. Neither of them looks quite right, but then, neither one looks quite wrong, either. Poking around in dictionaries online isn’t helping, sometimes they have it one way and sometimes the other. It actually looks like both of them are accepted spellings of the same word, and Google says they come up with almost equal frequency (“wooly” has 7.5 million hits, while “woolly” has 8.3 million, giving it a slight edge but hardly an overwhelming win). So should I pick one spelling and stick with it, or should I alternate spellings so that when people search for “wooly aphids” they will still find this “woolly aphid” page?

[2] Formic acid (HCOOH) is an extremely simple acid molecule, it is basically what you get when you stick a couple of hydrogen atoms onto carbon dioxide. In water, it ionizes[4] to form H[+] and HCOO[-], and is a moderately strong acid as organic chemicals go (it is more acidic than the acetic acid in vinegar). It got its name because it was originally isolated by distilling crushed ant bodies (“Formica”[3] is the latin word for “Ant”). Formic acid is used by the ants as a defensive chemical; ants with stingers use it as a venom component, and those without stingers either spray it at attackers or shoot it into wounds that they create by biting. It seems like I once read somewhere that they also use it as an antibacterial/antifungal agent around their nests, but I can’t find a reference for that at the moment.

[3] You might note that this has the same spelling as the plastic composite material Formica, which is widely used for countertops. My understanding is that they are pronounced differently, though: when applied to ants, it is pronounced “FOR-mic-a” (with a short “i”), but the plastic is pronounced “for-MI-ca” (with a long “i”)[4]. It turns out that there is no connection between the two names other than spelling, though. I had thought that maybe the plastic used formic acid as a curing agent for the polymer, but upon looking it up I see that it doesn’t. The name of the plastic actually comes from the fact that it was originally developed as a replacement for the mineral mica as electrical insulation. It’s a replacement “for mica”, see?

[4] Along the lines of different pronunciations of identically-spelled words completely changing the meaning, here is a question: How do you pronounce this word?

“unionized”

If you were thinking in terms of chemistry or physics, then you probably thought of an electrically neutral atom or molecule, and pronounced it as “un-ionized”. But if you weren’t, then you most likely thought of trade unions and pronounced it as “union-ized”.

I read a lot of technical papers that talk about ions in solution or in plasmas, so I reflexively read it as “un-ionized”. Which gives me a small bit of amusement when I’m reading newspaper articles and they start talking about unionized workers, and I think “well, I hope so, otherwise they would either be balls of expanding plasma, or puddles of dissolved salts!”