They're creepy, crawly, icky and sometimes even scary, but not all insects are pests. Some should be encouraged to stick around, and you should actually go out of your way to lure them to your garden. These natural predators will keep harmful insects in check.
When you reach for the spray can, you can cause more harm than good. Garden helpers invariably get caught in the crossfire, and you often end up wasting money and exposing yourself and your garden to potentially harmful ingredients in the process. Pesticides should only be used against true pests, and even then, only as a method of last resort in cases of real infestation. Try to select the least toxic product available.
Here are six beneficial insects everyone should recognize, the roles they play in a healthy garden and suggestions for plants that will encourage them to stick around, according to the National Garden Bureau and the Home Garden Seed Association.
1. Syrphid Flies
Striped and sometimes mistaken for bees, syrphid flies don't sting. Flying adults sip nectar from flowers, pollinating them in the process. Females lay eggs on leaves, usually near colonies of aphids. The half-inch larvae are important predators of scales, thrips, mites and aphids. Grasping prey with its jaws, the larva sucks them dry. A single syrphid larva can consume hundreds of aphids in a month.
Sweet alyssum provides the nectar of choice, but catmint, yarrow, buckwheat and cilantro also are draws.
Indefatigable pollinators and generally nonaggressive, there are as many as 50 species of bumblebees, none of which persist from year to year. Classified as "buzz pollinators," bumblebees shake flowers as they feed on nectar, which benefits certain types of flowers, particularly tomatoes.
Bumblebees are not picky. Clover, sunflowers, mint, coneflowers, asters and tomatoes are among the many flowers they like. To keep them in the garden all season long, plant flowers that will bloom in spring (like hellebores,) summer (butterfly bush) and fall (dahlias).
3. Parasitoids (parasitic wasps)
As if conjured up by a science-fiction writer, female parasitic wasps target suitable host insects and then lay their eggs onto or into their prey. The larvae that hatch feed on the host, essentially eating it alive from the inside out, ultimately killing it. You might have noticed tomato hornworms with dozens of white silken cocoons attached to their backs. In those cases, it's best to leave the hornworms alone; the parasites are busy eradicating them for you. Mummified aphids, dark-colored whiteflies and swollen, limp cabbage loopers also may indicate the presence of a parasitoid.
Plants in the carrot, sunflower and daisy families are very desirable, so consider planting dill, cilantro, eryngium, parsley, asters, goldenrods and sunflowers. By planting annual and biennial flowering plants in vegetable beds, and perennials along the borders, you can attract parasitoids exactly where you need them.
Lacewings feed on pollen, nectar and honeydew excreted by aphids. Though some adults feed on prey, the larvae do most of the work, earning the nickname "aphid lions." They use their piercing-sucking mouthparts to attack aphids, insect eggs, thrips, mites, mealybugs, immature whiteflies, small caterpillars and other soft-bodied insects, and then suck out their insides.
Plant flowers that allow easy access to nectar, as you would to attract parasitoids (those in the carrot and sunflower families). It's best not to be too quick to soap-spray aphids; give beneficial insects a chance to find them. Spraying aphid-infested plants with one tablespoon of sugar per cup of water may help increase lacewing and ladybug populations.
5. Lady beetles
Commonly called ladybugs, both adults and larvae are voracious eaters of scale, thrips, mealybugs, European red mites and aphids. Their populations tend to synchronize naturally with those of their prey. If plants are infested, you can purchase lady beetles by the box in local garden centers.
Most trees, shrubs and flowers, especially yarrow, dill, butterfly weed, coriander, fennel, sunflower, marigold and dandelion, will attract ladybugs, as they need to consume large amounts of nectar and pollen in order to reproduce.
6. Tachinid flies
There are more than 1,300 species of tachinid fly in North America, some of which can be easily mistaken for houseflies. Others, however, have prominent bristles. Predatory against corn earworm, imported cabbage worm, cabbage looper, armyworms, stink bugs, squash bug nymphs, Japanese beetles, sawfly larvae and more, some tachinid flies lay eggs where caterpillars will eat them and then wreak havoc on the internals of their host. Others insert eggs directly onto or into their prey. Either way, eggs hatch and maggots grow within the host, killing it.
Use plants in the carrot, sunflower and mint families, in much the same way as you would attract parasitic wasps.