While some gardeners still think that any bug in the garden is a bad bug, change is in the air. Most plant-lovers now realize that insects and plants go hand-in-hand and that there are far more beneficial insect species than there are harmful ones. In fact, of Earth’s million insect species identified by science, less than 1% are classified as known agricultural or human pests. That means that the vast majority of insects we encounter are either benign or beneficial.
Aside from valuable pollinators, there’s another group of beneficial insects worth getting to know. Often called “natural enemies” or just plain “beneficial insects,” the role of this group of important insects is pest control. Yes, bugs eat bugs, and as it turns out, this natural predation plays a huge role in controlling pests in our landscape.
Today, I’d like to introduce you to just five members of this important category of insects. You’ve likely encountered them in your own garden over the years. Perhaps you didn’t know who they were or what they do, but from now on, you’ll know how valuable these five insects are in keeping pest numbers to a minimum.
This is North America’s largest and most important group of parasitic flies with 1,300 different species. Adults, at first glance, resemble small houseflies covered in dark, bristly hairs. They measure 1/3- to ¾-inch long.
The adult flies are important pollinators while their young are the pest eaters. They’re parasitoids because female tachinid flies deposit eggs or live larvae directly onto the bodies of host insects including various caterpillars, beetles (including Colorado potato, Mexican bean, Japanese and cucumber beetles), squash bugs, sawfly larvae, four-lined plant bugs and many others. The egg hatches, and the larvae tunnel into the host’s body. They consume their host and eventually kill it.
Some species also lay eggs on plants in hopes that they’ll be ingested by a host as the plant is eaten. Most often, the fly larva then pupates within its host and emerges as an adult.
Since adult tachinid flies use nectar and pollen as a food source, they’re attracted to habitats rich in flowering herbs, particularly those in the dill (Apiaceae) family. Cilantro, dill, fennel, golden Alexander and parsley are attractive to them, as are members of the daisy family including aster, chamomile, feverfew, ox-eye daisy, coreopsis and Shasta daisies.
Hover or syrphid flies
Many species of hover flies look much like small wasps or bees, with a black and yellow striped abdomen. They do not have the ability to sting and aren’t harmful to humans despite their wasp-ish looks. The ¼- to ½-inch long adults can hover like a hummingbird as they drink nectar from flowers and are important pollinators. It’s the larvae that control pests.
Hover fly larvae are small, brown or green maggots that hatch from eggs laid on plants infested with pests. Each larva can eat up to 500 pests before maturation.
Adults cannot reproduce without pollen as a food source, and because they don’t have specialized mouthparts (nor do many other beneficial insects), plants with very shallow flowers are attractive to them. Plants like alyssum, aster, coreopsis, cosmos, daisies, fennel, mint, sunflowers, wild mustard and dill are great choices.
To maintain a steady population of these predators, make sure something is blooming in your garden from the last frost in spring to the first frost in fall.
Minute pirate bugs
Measuring a mere 1/16 inch, the oval shaped adult is black with white wing patches. The teardrop-shaped nymphs are even smaller and are orange or yellow in color. Both are surprisingly fast moving, and both feed by piercing prey with their needle-like “beaks.”
Minute pirate bugs feed on spider mites, thrips, aphids, insect eggs, small caterpillars, lace bugs, scale, whiteflies and others. To attract them to the garden, plant lots of spring-flowering plants.
Since minute pirate bugs are often the first predators to emerge in the spring, before prey becomes readily available, they depend on early-season pollen and plant sap as a food source. Good plant choices for this beneficial include: basket of gold, oregano, sage, wallflower, wild mustard, alfalfa, crimson clover and parsley.
There are over 6,000 different species of parasitic wasps in North America. These tiny, non-stinging wasps are some of the most beneficial insects in the garden and are known to parasitize more than 300 species of pests.
Most species of parasitic wasps measure between a minute 1/32 and ½ inch in length. Some species have pointed ovipositors (the term for the female’s egg-laying apparatus) that look a lot like an exaggerated stinger but they’re only used for laying eggs.
Most female parasitic wasps lay eggs inside or on host insects. The eggs hatch and consume the prey, eventually killing it. Some species pupate in external cocoons (including the cotesia wasp that attacks tomato hornworms) while others pupate within the host’s body (like the tiny Aphidius wasp that attacks aphid colonies).
Depending on the wasp species, they help control: aphids, beetle larvae, bagworms, cabbage worms, potato beetles, corn ear worms, cucumber beetles, cutworms, caterpillars, Japanese beetles, leafminers, sawfly larvae, squash vine borers and many, many others.
Adult wasps consume nectar and pollen, and they’re attracted to plants like allium, alyssum, cosmos, dill, fennel, thyme, yarrow, coneflowers, sunflowers, helianthus and others.
These beautiful, slender insects are attracted to lights and are commonly found clinging to window screens on summer nights.
The adults are light green with huge, transparent wings, threadlike antennae and golden eyes. They measure up to an inch in length and consume pollen and nectar exclusively.
Adult lacewings lay eggs on the ends of long filaments to prevent the new hatchlings from turning to cannibalism. Several eggs lined up along a blade of grass look much like little lollipops in a row.
The lacewing larvae that hatch from these eggs are fast-moving, flattened, brown and white creatures with large, curved mandibles for grasping prey. Lacewing larvae are big time protein eaters! They’re only ½-inch long but can consume up to 100 aphids per day – appropriately earning the nickname “aphid lions.”
To lure them in, plant angelica, caraway, coreopsis, goldenrod, yarrow, tansy and even dandelions.