Pests controlling the pests
Running with impressive alacrity from the porch-rail wasp nest you’ve just disturbed, or blasting it into oblivion with half a can of bug spray, you probably haven’t noticed, or don’t care, that there aren’t many flies hanging around your front door. All wasps (which includes yellow jackets and white-faced hornets) are, for all the fear their truly impressive stinging capacity induces in us, voracious predators of thousands of other insect species and thus play a vital role in limiting the populations of numerous pests, including the too-familiar tormenting, germ-carrying, food-contaminating fly.
In fact wasps feed abundantly on all kinds of nuisance species such as corn earworms, hornworms, blow flies, mosquitoes, and caterpillars, including those of the gypsy moth. They also seek out flower nectar, playing an important role in pollination. Therefore, contrary to our usual perception of them, the diverse varieties of wasps and their kin are actually beneficial insects, a hazard to us only when they build their nests too close to our own dwelling places.
“If wasps were not out there busily killing agricultural pests,” observes the noted science writer Richard Conniff, “we would starve.”
And oh yes: only the female wasp stings. You could grab a male wasp right off the windowsill bare-handed and it would buzz furiously between your fingers, even poke at you with its stingless behind, to no avail –it can’t hurt you at all. Assuming you have correctly identified its gender, of course.Be especially sure of this distinction if you live in or visit the southwest and happen to run across the large, aptly named tarantula hawk Pepsis wasp. This female’s stinger can be up to a third of an inch long, with a venom jolt described by entomologists in the know as “kind of profound.” Or to quote the Schmidt Sting Pain Index, which places the tarantulahawkwasp at the top of the list: “Blinding, fierce, shockingly electric.. . a running hair dryer has been dropped into your bubble bath.”
In other words, leave Pepsis alone (good wasp advice overall); its venom serves a purpose in desert ecology. The female preys on its namesake, paralyzing the giant spiders with one quick sting and burying them in the sand with a single egg laid against each tarantula’s abdomen. The living, immobilized spider will provide fresh food to the developing wasp larva for as long as a month before it finally dies. ‘Nuff said.Though tarantula hawks have not, so far, migrated to the northeast, we’re not exactly out of the Schmidt Sting Pain Index woods. Buzzing a mere point under Ms. Pepsis on the Schmidt scale is the familiar northern paper wasp (“caustic & burning, like spilling a beaker of hydrochloric acid on a paper cut”). Considered less aggressive than other members of its family, Polistes fuscatus is a social insect, living in colonies made up of a queen, infertile female workers, and male drones. They are relatively large (about an inch long) and slender, reddish-orange with a distinct yellow stripe and long legs.
As with other members of the order Hymenoptera (60,000 of which, including ants and bees, possess some form of stinger), it is the paper wasp female that hunts for food and constructs the unprotected umbrella-shaped nest-on-a-stalk. Each colony lives but one year; only the inseminated queen survives the winter, hiding in hollow logs, under bark and leaf litter, or inside houses and other structures.
Emerging in late April or early May, the P. fuscatus queen immediately chooses a site and starts building a series of horizontal six-sided cells made from chewed wood fragments mixed with her saliva. She lays one egg in each cell. The cell ends are open, exposing the heads of the developing larvae, which the queen feeds by chewing caterpillars to a pulp and stuffing the pulp solids into the larval cells. She and her eventual brood of mature wasps eat the fluids released by this pulping process, as well as flower nectars and juices of ripening fruit.
Thus the wasp world reverses the usual food role of nature: juveniles feed on solids while adults drink the liquids.
When larvae are ready to pupate, the queen covers the cells with silk, forming little domes over the openings. From these the female workers emerge, ready to assume their tasks of nest expansion, caring for the queen and new larvae, food foraging, and defense. This allows the queen to focus all her energy on egg-laying. By season’s end, a P. fuscatus nest can harbor 200 or more workers. Male drones hatch later in the year and die soon after fertilizing the queen or new queens, their sole function in life.
Paper wasps may be less aggressive than yellow jackets or white-faced hornets, but they will most assuredly defend their nests if disturbed, and all wasp venom contains factors that release histamine, a compound that dissolves red blood cells. For about 1 percent of the population even one sting can be fatal; and as people often learn the hard way, each individual wasp can sting many times. Removing nests near homes and other human activity is therefore a necessity.
Otherwise, paper wasps should be left alone. They feed on pest caterpillars, contribute to pollination, and themselves provide food to birds and other species. In any case, P. fuscatus colonies will not survive the winter.
Moreover, the introduced European paper wasp (Polistes dominulus) has begun to alter the paper wasp playing field. First discovered near Boston in the late 1970s, P. dominulus is a smaller, more efficient colonizer than the northern paper wasp and has spread rapidly across the United States. Native to Mediterranean countries and parts of China, these yellow and black-striped invasives are frequently mistaken for yellow jackets. But they are in their way far more troublesome than yellow jackets.
For one thing, unlike the habits of northern paper wasps, P. dominulus queens will use nests of either species from the previous year, thereby giving them a reproductive head start. In further contrast, European paper wasp queens are cooperative; more than one queen will colonize a given nest. Theyprey on a wider variety of insects and caterpillars, further benefiting early and rapid development of its larvae. In some areas, European paper wasp colonies have produced 2.5 times the number of workers as the native species. Entomologists warn that northern paper wasps are declining, probably as a result of this competition, with unpredictable ecological consequences.
Of more immediate concern to people, the European species prefers to build nests in enclosed voids, unlike the more visible colonies of northern paper wasps. Tucked behind shutters, inside outdoor lighting fixtures, bird boxes, and infrequently used outdoor equipment such as gas grills and covered boats, the unseen nests of P. dominulus can provide a nasty surprise. The species has lately become prevalent in urban areas, notably in unexpected places like parking meters, pedestrian crossing lights, and abandoned cars.
Staying alert to early nest-building by these yellow jacket look-alikes, when only the founding queens are present, makes it easier to knock the nest down and keep them out of outdoor fixtures and gizmos. But keep in mind that if the queen survives, she will find another nook somewhere and start building a new nest.
Several spiders jammed inside the tube later, the dauber lays a single egg on one of them and seals off the chamber with a cross-wall of mud. Then she extends the tube and repeats the process over and over, sometimes creating a half dozen or more chambers. Then she moves on, to build more nests elsewhere.
Nest construction is often accompanied by bursts of buzzing that are amplified by hollow tube acoustics. During this process, the male mud dauber hovers ominously, guarding the nest while the female forages. But his posturing and strafing is a bluff. As with other members of the wasp family, the male has no stinger. Even female mud daubers rarely sting. As such, they are considered a nuisance rather than serious pests. The nests can be scraped off and discarded; since the daubers are solitary, there is no worker caste with which to contend.
Black and yellow mud daubers construct globular nests with one or more cells, also provisioned with spiders. The iridescent blue mud dauber takes over nests made by the black and yellow dauber, but the blue dauber preys specifically on black widow spiders for larval food, providing in the process an inadvertent beneficial service to people.
The potter wasp, another type of mud dauber, attaches its unique juglike single-chambered nest cells on twigs and branches of trees and shrubbery. These daubers prey on moth caterpillars, placing up to a dozen of them in each sealed larval chamber.
Some species of potter wasps nest in the ground, in hollow plant stalks, nail holes in wood, or deserted nests of bees and other wasps. Mason wasps inhabit the abandoned cells of black-and-yellow mud daubers and occasionally use old carpenter bee tunnels or burrows of ground-nesting bees. In these spaces it builds a series of mud-walled chambers stuffed with paralyzed cutworms.
Meanwhile, a cuckoo wasp is probably lurking nearby. So named for the European cuckoo bird, which parasitizes other bird species’ nests, these tiny, colorful wasps are themselves parasites, of mud daubers, bees, and sawflies, to name a few. The cuckoo wasp female waits for the chance to sneak inside the host chambers and lay her own eggs or steal the food spiders. In either case, the host larva dies.
There are about 230 species of cuckoo wasps in the US and Canada, providing check-and-balance within wasp ecology, among other benefits. For example, one variety of this species lays its eggs on the pupae of blowflies that are serious parasites of bluebird and tree swallow nestlings.
Yet another beneficial member of the wasp order is the Ichneumon, an eye-catching creature to say the least. Of the 70,000 ichneumon species worldwide, about 3,000 live in the US. They are parasites of caterpillars, beetles, flies, and pigeon tremex horntails, a type of ancient wasp. The female long-tailed ichneumon can locate horntail larvae deep inside tree trunks, using her antenna to detect the scent of a fungus deposited with the horntail eggs.
Amazingly, the ichneumon then drills down through several inches of wood with her hair-thin ovipositor, a three-inch specialized stinger about twice as long as she is, and with it lays her own eggs on the horntail larvae. And yes, she can and will sting if “improperly handled.” Which means –don’t. Ichneumons are not aggressive and will leave you alone if you offer them the same courtesy.Then there is the velvet ant –the common name for a family of wingless wasps that looks like large, furry ants. They are not ants. Also known as cow-killers because of the female’s painful, long-lasting sting (which does not, in fact, kill cows but still rates 3 out of 4 on the Schmidt scale), velvet ants are parasites of flies, bumble bees, caterpillars, and other wasps. The female can also bite and is, in the words of one entomologist, “on a perpetual short fuse, weapon always at the ready.”
Gall wasps are a group made up of more than 1,250 species of diminutive wasps that parasitize plants by sting-inducing the formation of strangely shaped swellings on stems and leaves. The wasps then lay their eggs in these protrusions, which provide shelter and food to the developing larvae.
Along with fungi and bacteria, there are many insects that create galls, including aphids and mites. But wherever there are oaks there are gall wasps, which attack all parts of these trees including roots, leaves, twigs, and even the acorns. Saliva from wasp larvae further stimulates and alters the galls from within. Large galls can be seen on oaks year-round. Larvae develop in separate, hardened chambers inside the galls and chew their way out when mature.
Gall wasps have complicated life cycles, producing these growths in an endless variety of shapes and colors. Sometimes alternate generations of wasps produce distinctly different galls. Oak spangle galls resemble small buttons on the surface of oak leaves. Other wasp-induced leaf galls look like blisters, beads, fuzzballs, or sets of moose antlers.
Though the majority of galls are not injurious, some of these galls can cause the death of the tree over time and should be pruned off. Galls can also appear on roses, berry bushes, flowers, and many other plants and are certainly some of the oldest curiosities of nature. The fossil record shows that insect-induced galls existed 225 million years ago during the Triassic period in France.
Oak leaf gallsGalls were a well-known source of tannin in the early manufacture of inks and dyes as well as livestock feed and hair restorative formulas. Medicinally, gall ointments have been used as an eyewash and to stop nosebleeds, shrink inflamed tonsils and painful hemorrhoids, and to soothe bleeding gums (hopefully not all with the same applicator). Gall extract injections were recommended in folk medicine as a cure for gonorrhea. In ecological terms, the abandoned galls provide refuge and food for many insects, including solitary bees, spiders, and other types of wasps.
Just incidentally, the wasps that emerge from galls will not sting humans.
In sum, the parasitic habits of the wasp family have benefited humans throughout history, far more than their stings have caused us woe, and in recent times those habits have been, in a way, parasitized by us for the benefit of human agriculture.
Apple growers in the northeast owe much to the tiny Peristenus digoneutis wasp imported from Europe in 1979 by the Beneficial Insects Introduction research lab in Newark, Delaware. Its mission was to control the tarnished plant bug, a pest of fruits, vegetables, seed crops, tree seedlings, and cotton. Tarnished plant bug infestations have cost farmers billions annually in crop losses and chemical controls, not to mention the hazards of using those controls in the first place.
Rather than release P. digoneutis wasps directly into these crop fields, entomologists introduced them to alfalfa fields where tarnished plant bugs feed and multiply. When the alfalfa is cut for hay, the bugs fly off and infest other crops. Since their introduction, digneutis wasps have reduced tarnished plant bug numbers in these fields by 65 percent. At the same time, infestations in apples and strawberries in contiguous states have been reduced by about the same amount. This ingenious and apparently successful use of an introduced species is being carefully monitored, with plans to extend digneutis populations incrementally.
And these are only a few of the wasp family members. So keep in mind as you aim to blast that bug spray all over the side of your house that even a small colony of paper wasps hanging by your front door live there at the expense of thousands of flies, gnats, and mosquitoes that would be actively invading your personal space if they hadn’t been chewed into wasp baby food already by those formidable, busy workers.