One of the pleasures of doing this column is that readers sometimes write to me with natural history questions. Recently, Susan, in College Park, sent a picture of small white blobs atop hairlike stalks on the leaves of her butterflyweed. The stalks, she said, were about an inch long, and the blobs at the end the size of the glass beads on top of dressmakers’ pins. She also noted that the butterflyweed was covered in aphids. Could the blobs be aphid eggs?
Eggs, yes, but not aphid eggs. Rather, the eggs belonged to one of the aphids’ deadliest enemies — green lacewings — and they were deposited with care by the female lacewing near a ready supply of prey for her young.
It’s hard to imagine a less likely candidate for a fearsome aphid menace than the gauzy green adult lacewing, delicate and fragile as the lace from which it takes its name. Not so the lacewing larva — a tiny crocodilian terror with long jaws they use to impale their aphid snacks and suck the lifeblood out of them.
Lacewings belong to the large insect order Neuroptera, loosely translated as “netwings,” from the Greek “neuro” (nerve or net) and “ptera” (wing). The 6,000 or so species worldwide are characterized by their mostly transparent wings with a fine, net-like tracery of wing veins. Neuroptera also include antlions and owlflies — and popular as fly fishing models — the fishflies, alderflies and dobsonflies.
Lacewings, though, are the fashion plates of the order. Here in the DMV, they come in two broad categories: green lacewings and brown lacewings. Green lacewings comprise the insect family Chrysopidae, derived from the Greek “chrysos” (gold) and “ops” (face) — a nod to their stunning beauty. Our most common green lacewing, the golden-eyed lacewing (Chrysopa oculata), sports brilliant golden eyes to complement its diaphanous green wings. There are 20 or so green lacewing species in our area; adults average about an inch long, not including another half inch of antennae. Green lacewings aren’t always green, however; they can also be pinkish, yellowish, or — confusingly — brown.
The dozen species of brown lacewings in our area (family Hemerobiidae) are always brown and usually have wings that are less translucent than their more jewel-hued cousins. They’re also smaller, about a half-inch or so long, with antennae only about half the length of their bodies.
Both brown and green lacewing adults are capable fliers, and we often see them at night on screened windows and doors, or around porch lights. They are active from early spring until the first frosts of autumn. They’re quite common, and you’re much more likely to see lacewing adults than you are the larvae.
During the day, lacewing adults are often seen on flowers, where they feed on nectar and pollen and meet up with potential mates. Once she’s mated, a female lacewing goes in search of aphids — she has very sophisticated olfactory senses that can detect the scent of aphids and, even more intriguingly, the scent given off by plants in distress from an aphid infestation. She homes in on that chemical signature and picks a leaf or twig near this ready food source on which to lay her eggs.
Lacewing eggs are a marvel in their own right. The female first draws a long, very thin strand of silk from her abdomen, as long as her body, and at the top of the stalk places a single pearly egg. She may “plant” a garden of dozens of these stalked eggs. Why the high-altitude egg pedestals?
First, they reduce cannibalism. Lacewing larvae are voracious predators, and if a sibling happens to be nearby when one hatches, it’s likely to become big brother’s or big sister’s first meal.
But even more importantly, the long stalks loft the eggs out of reach of ambling ants. And where there are aphids, there are almost always ants. Many aphids produce a syrupy sweet liquid from their butts that ants find irresistible, and in exchange for this sweet treat, the ants protect aphids from roving lacewing larvae. Lacewing larvae are such effective predators of aphids and other small insects that the eggs are sometimes sold as a biological control in lieu of chemical pesticides.
Up close, lacewing larvae could be diminutive doppelgangers for the bloodthirsty main characters of the “Alien” movie franchise. Their jaws are massive, relatively speaking — sometimes a third of the body length — and wicked sharp, lined with jagged teeth that grab and impale hapless aphids. For all its heavy armament, that jaw is hollow, and for good (and rewarding) reason: It both pumps the victim full of a cocktail that dissolves its insides, and then reverses flow to suck out the resulting aphid smoothie.
Some species of lacewing larvae even affix the grisly husks of their recent dinners to spines along the lacewing’s back and sides, fashioning an effective camouflage against ant patrols. Other lacewing larvae pile bits and pieces of lichen, dead leaves and other debris onto their backs — what looks like a lichen on the move across a tree trunk is likely a lacewing on the hunt!
Lacewing larvae aren’t afraid to punch well above their weight for potential meals, either. They’ll even take a nip out of an unsuspecting human arm if they happen to stumble across one, although they can’t really draw blood or inflict any harm beyond an annoying pygmy pinch!
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Rick Borchelt is a local botanist and science writer who gardens and writes about natural history. Reach him with questions about this column at rborchelt@gmail.com.