Exclaiming over the lovely colors, I went to put the bouquet of bearded irises into a vase. As I took out a sharp pair of scissors to cut the stems to size, I noticed a bumpy layer of pale green… something, tucked into the crevices between the leaves. On closer inspection, I realized they were aphids. OK, sort of gross, but not terminally so. Then I realized I had smooshed aphid bodies all over my fingers.
Aphids, also called plant lice, have got to be one of the most pathetic of plant pests. They’re so defenseless! You can kill them with pretty much anything—insecticidal soap, organic pyrethrin–even a strong jet of water will knock them off their perches. Once on the ground (assuming the fall didn’t kill them outright), they’re too feeble to crawl all the way back up the stem, so they lie there and die. Talk about wimpy!
I’m convinced that the only reason that aphids haven’t gone the way of the dodo is that there are so darn many of them. If you can’t win through big brains or brute strength, try overwhelming numbers.
For most of the year, all aphids are females. Males aren’t needed, as the females clone themselves to produce three to five identical daughters per day until they die. This is a photo by MedievalRich at the English language Wikipedia of an aphid giving birth:
Given that their natural lifespan is about a month (unless they’re eaten first—we’ll come to that), that means that each mother produces 120 daughters. These daughters reach maturity in a week or two, and start imitating mom, so you can see how the aphid population can soar.
I should point out that there are male aphids. At the end of the growing season, instead of clones, males and special, sexual females are produced. They mate, creating offspring that can lay eggs. The eggs are stashed away in protected spots for the winter. In the spring, they hatch—and the cycle starts all over again.
If you look closely at a plant infested with aphids, you might notice that some have wings and some do not. The winged forms are produced when the plant the aphids are feeding on begins to decline. That gives some of the group a way to get to a new food source.
Lacking the kind of insect jaws that movie producers love to enlarge on the screen, aphids are truly little suckers. They poke their snouts into the leaves on which they find themselves and suck out the juices. Apparently, they’re incredibly efficient at this, since they excrete excess sugar in the form of honeydew.
This honeydew, a sticky, viscous liquid, is a boon to other insects. Such largess is not to be wasted. You probably already know that ants protect “herds” of aphid from predators so they can feed on the sugary goop (right). Sooty mold also gains nourishment from honeydew, sometimes becoming a more serious problem than the aphids ever were. The gray-to-black stuff covers the leaves, preventing light from reaching them. With no ability to photosynthesize, the leaves die. And if you’ve ever parked your car beneath an aphid-filled tree, you know what that honeydew does to the paint job!
With such reproductive potential, why isn’t the world overrun with aphids? Plump and nutritious, aphids are eaten by all sorts of other creatures. Carnivorous insects, especially the larval forms of ladybugs, lace wings, and syrphid flies, relish them. (You may recognize syrphid flies by their more popular names—flower fly or hover fly.) Parasitic wasps lay eggs on them, and the larvae eat their way out, leaving aphid mummies behind. Spiders take their toll, too. Then there are larger predators, such as lizards and hummingbirds. Life as an aphid is pretty precarious.
Aphids come in a variety of colors, representing different species. In fact, nearly every plant supports at least one species of aphid! There are over 350 different kinds of aphids just here in Colorado. It will be a relief to know that most aphids don’t really harm their hosts—there are just a few that really cause problems.
Given the ubiquitous presence of aphids, I’ve taken to careful inspection of the groceries I bring into my kitchen. I frequently wash them off of lettuce and other leafy greens, and I’ve seen them on broccoli as well. For years, a humorous story has made the rounds of our local master gardener classes. Apparently a group of entomologists were attending a fancy banquet at an elegant hotel in Denver, when one noticed aphids in the salad. He promptly identified them, and everyone rushed over to see. The scientists were fascinated, but the hotel was mortified!