The recent fall weather in Austin has been gorgeous, and yesterday, for the baker’s dozenth time this October, I went out to see what natural wonders I could photograph. What first caught my attention was some poverty weed, a type of native bush that turns all plumy this time of year; but as sometimes happens, when I got close, I noticed something more interesting than what first attracted me. Near the tip of one willowy branch of the poverty weed I saw that some ants were herding a group of yellow aphids.
“Okay,” you say, “I may let you get away with saying baker’s dozenth instead of thirteenth, but herding? People can and do herd cattle, but can one type of insect herd another? Don’t insects prey on other insects?” According to the best sources—which is to say the ones I’ve been able to find without looking very hard—ants have occasionally been seen to eat aphids, but much more commonly the two creatures exhibit what biologists call mutualism. Aphids extract juices from plants, and in the process they excrete a sweet-tasting substance appropriately called honeydew, which ants are crazy for. The ants keep aphids around for that delicious bounty, and they really do herd them. Ants will sometimes pick aphids up and move them to a place where juices are more plentiful, even to a healthier plant in the vicinity. In return for having a continuing source of sweet food, the ants will attempt to fight off or kill any aphid predator that comes along, and during the winter some ants protect aphid eggs from the cold by storing them in their own underground nest.
“Fascinating,” you say, “but I’m reading this column to learn about etymology, not entomology.” All right, I was coming to that. Linnaeus, the great 18th-century categorizer of plants, created the genus name Aphis, with stem Aphid-, as if it were a Greek noun, but why he chose what we now call an áfido/aphid isn’t clear. The Oxford English Dictionary notes that “a number of conjectures are offered…, the least improbable being that the plural is for Greek apheides… ‘unsparing, lavishly bestowed’ (? in reference to their prodigious rate of production, or to their voracity)….”
Spanish more commonly calls an áfido a pulgón, basing the word on pulga ‘flea,’ even though aphids don’t bite people the way fleas do. English has called the aphid a plant louse, whose first word differentiates it from the type of louse that plagues people; English has also used the term ant-cow, which captures the herding nature of the ant-aphid relationship.
©2010 Steven Schwartzman