Beneficial Insects: Get to Know the Good Garden Bugs

Familiarizing yourself with beneficial garden insects is an important step toward keeping pests away and your garden healthy.

Beneficial insects

Spiders, lady beetles and praying mantises are all insects that may help keep your garden robust.

Photo courtesy Storey Publishing

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Tammi Hartung shares her successful methods for attracting pollinators, nourishing soil and deterring pests in The Wildlife-Friendly Vegetable Gardener (Storey Publishing, 2014). Because virtually every garden has pests — animals and bugs that wreak havoc on healthy plants — getting familiar with beneficial insects is a natural, proactive measure toward keeping garden pests at bay. Learn more about good bugs in this excerpt from Chapter 4: “Attracting Pollinators and Beneficial Predators.”

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Beneficial insects manage pests that seem to come to every vegetable garden at some point during the growing season, so a wise gardener makes them welcome. Each type has its favorite prey, so it is quite important to encourage a diverse community of them in the garden space. These “good bugs” consist of both insects and spiders (which are arachnids, not insects). Before you can welcome predators into the garden, you must be able to recognize which are helpful and good and which are pests. Once you can distinguish which bugs you want to encourage, and which you do not want wreaking havoc, you can begin to welcome the beneficial ones to help you eradicate the pests.

Meet the Beneficial Insects

A lady beetle larva will eat 25 aphids a day and the adult lady beetle will eat as many as 60. Both adults and larvae feed on soft-bodied pests, such as caterpillars as well as aphids. Most adults have bright-colored wing shells that are orange, yellow, or red with black spots, but some have black shells with orange spots. The larvae look totally unlike beetles — they have black elongated bodies with yellow or orange markings on them.

Adult lacewings are lovely creatures with translucent, sparkling wings on green or brown bodies. Green lacewings frequent gardens, whereas their brown cousins prefer more cover and tend to live in trees and shrubs. Lacewing larvae, sometimes called aphid lions, have hooked jaws and look a bit like alligators. They are aggressive hunters of many pests, including aphids, mites, and leafhoppers. Green lacewing eggs are easy to recognize; laid individually or in clusters, they have a silken, threadlike stalk that attaches them to a plant.

Spined soldier bugs look like their relatives the stinkbugs, having that same armor-type shell. They produce the same disagreeable odor if crushed. Unlike pest stinkbugs, spined soldier bugs mostly eat caterpillars, by stabbing them with their sucking mouthparts. They are common in gardens and very beneficial.

Tachinid flies look a bit like the common housefly, only slightly larger. These parasitic flies lay their eggs on or in the soft-bodied larvae of earwigs, caterpillars, beetles, and grasshoppers. When the eggs hatch, the larvae devour their host. A few species of tachinid flies lay their eggs on plant leaves, hatching inside the host insect after it has unknowingly eaten the eggs while munching on the leaves of the plant.

Praying Mantises

A familiar predator in the garden is the praying mantis, which gets its name because while hunting it holds up its front legs as though praying. This insect comes in green and brown and sort of resembles a twig, except that this twig moves and has large eyes on the outside edges of its head. Mantises often occur naturally in the garden, hatching in spring from an inch-wide egg sac that overwinters among perennial plants. (A good reason not to trim back and tidy up perennials in the garden until later in the spring is that these plants provide good habitat for many beneficial insects as well as seeds for wild birds.) These insects hatch out as tiny beasts about 1/4 inch long, but reach 2 to 4 inches when fully mature. They are cute as anything, especially when they’re tiny. Not shy around humans, they’re fairly easy to watch while working in the garden. Despite being cute, they are ferocious hunters of insects. Unfortunately they eat any insect they can catch, including beneficial insects and pollinators. They also cannibalize each other, especially when they’re small, until only a few are left within the boundaries of even a large garden landscape. Famously, the female often does in the male after she has mated with him.

Praying mantises are large enough to take on big insects such as grasshoppers and crickets. Because grasshoppers can quickly devour plants in the garden, I welcome the one or two praying mantises that make their home in mine. Occasionally, we come across one that has found its way into a greenhouse; the praying mantis earns its comfy home in there by helping with greenhouse pest management. You can purchase praying mantis egg sacs in the spring, but it’s usually best not to encourage a huge population. It is likely you have a few in your garden already.

Spiders

Spiders have gotten a bad rap. The common thinking that all spiders are evil and should be squashed underfoot is simply wrong. Spiders are amazing hunters. They will patrol your garden, catching and eating all manner of insect pests. Notice how beautiful their webs are and how they sparkle when the morning dew is on them. Spiders come in any manner of colors and shapes. The common garden spiders we have are called banded argiopes and have striped legs that make them look almost comical. They sport yellow and black stripes or, less often, chartreuse and black banding. The banded argiope is a medium-sized orb weaver and is common in the western part of North America. Another helper in our garden is the monkey-faced spider (Araneus gemmoides), sometimes called a cat-face or humpback spider. It’s a sort of a peachy tan, with two orange spots on the back end of its abdomen on the underside. If you look up at this spider in its web, you may see what looks like the face of a monkey or perhaps of a cat staring back down at you. The monkey-faced spider is a very large orb weaver — I measured one on the porch at 1 1/4 inches across at the widest part of its body. They are good fly predators and create beautiful large webs in the greenhouses and in the garden.

Other species of orb weavers are common garden helpers in other parts of the country. Yes, there are spiders you should approach with care — the black widow and the brown recluse, for example — but they are few in number. The vast majority of spiders are helpful in the garden and deserve respect.

Wasps

Wasps are valuable in the food garden. Several excel at pest patrol, and a few are important pollinators. When most people think of wasps, they think of hornets and yellow jackets. These are social wasps, and they can be annoying. But there are also many types of solitary wasps, and most of them don’t sting.

Paper wasps (Polistes spp.) feed on caterpillars, earworms, beetles, and flies, in addition to some other insects. They can sting but usually will do so only if their papery nest is threatened in some way. Baldfaced hornets (Dolichovespula maculate) are tree-dwelling paper-nest wasps. They are also beneficial to gardens because they feed their young live insects, mainly caterpillars. They will also sting if their nest is threatened. Another useful wasp is the parasitizing trichogramma. This incredibly small wasp lays its eggs in the larvae of pest insects such as caterpillars, earworms, and whiteflies. When the eggs hatch, the larvae feed on the host, leaving behind only an empty shell. These very tiny wasps are especially helpful in a greenhouse.

Some wasps can be useful pollinators, although they’re not as efficient at this task as bees are. Most wasps feed on nectar only as adults in need of quick nourishment to transform into energy. These small solitary wasps are pretty, gentle creatures as they move around and through the flowers. They prefer those that are shallow-throated like those of fennel and members of the carrot family, such as carrots, parsley, and celery. They also pollinate garden flowers, among them goldenrod and butterfly weed. Pollen wasps (Pseudomasaris spp.) are the only wasps that actually collect nectar and pollen and take them back to the nest to feed their young.

For the most part, hornets and yellow jackets don’t bother anyone and simply conduct their business of foraging for insects or nectar and pollinating the flowers as they go. There are, however, some places where stinging insects are not welcome: right by a door or a table on a porch are two examples. In these cases, it’s best to remove a nest and look for ways to lure the wasps elsewhere.

Good Plants for Pollinators and Beneficial Predators

Many so-called weeds are wonderful fodder for both pollinators and predators, making it wise to practice a degree of tolerance when it comes to weed management, to maximize the variety and numbers of pollinators that will visit the garden. Some of these same weeds can provide food for humans as well. Take the notorious dandelion. You can use the tender leaves in spring as salad greens. Once they bloom, you can mix the yellow flowers with some minced onion, flour, and seasoning herbs and fry them up as dandelion fritters. You can also gather a large amount of the flower heads for dandelion wine. The chopped and roasted roots of dandelion can be used as a coffee substitute, much like those of chicory, a common roadside weed with beautiful blue flowers. Another edible weed is common purslane: large-leaved forms are a nice addition to salad mixes and are an excellent source of healthful omega-3 fatty acids.

Planting a variety of herbs in and around the food garden helps create a welcoming environment for pollinators and other beneficial insects, such as lady beetles, lacewings, moths, and butterflies. Chamomile attracts beneficial wasps and hoverflies. The large leaves of horseradish provide shelter for beneficial insects and spiders, and the plant may act as a decoy to lure grasshoppers away from other plants. When thyme is in bloom, it’s often covered with honeybees; have a good look before you harvest a handful of thyme to be sure you’re not grabbing a bee at the same time! Oregano and lemon balm are also wonderful for honeybees. Herbs add beauty to the garden and flavor to the kitchen.

Herbs typically are quite aromatic. They contain volatile oils, which supply their wonderful fragrances and flavors, even some medicinal properties. Many of those same aromatic oils act as deterrents to pests in the garden; mice are not crazy about the smell of strong mint, and deer usually avoid sage and lavender.

The wise gardener will grow many flowers around and inside the food garden to attract not only pollinators but also beneficial predators. Pest insects are often attracted to flowering plants that are highly fragrant — for example, sweet alyssum and other members of the mustard family. Have you ever noticed how sweet-smelling the flowers of arugula and radishes are? This is one of the reasons they can become infested with aphids or flea beetles. Predatory insects know that sweet-smelling flowers may be the perfect place to find dinner. The predators often lay their eggs on flowering plants such as yarrow and chamomile so that when the eggs hatch, the larvae will have a good supply of pest insects, as well as some -nectar, to feed on.

Strategically incorporating annuals and perennials in and around the food garden will assist you in pest control — and you’ll have the delightful added advantage of the color these flowers bring. Aphids are drawn to plants like marigolds, roses, chamomile, and angelica, so you’ll see plenty of lady beetles in all stages of their life cycle on the leaves and flowers of these same plants feasting on aphids. Cosmos — -cheerful annuals that add bright shades of pink, red, and white to the garden — attract spined soldier bugs, which are good predators of caterpillars and beetle larvae, such as of the Colorado potato beetle. I love the delicate lacy scabiosa, sometimes called pincushion plant. Scabiosa flowers provide great fodder for honeybees and also attract hoverflies, whose larvae forage on the aphids that may be lingering in that part of the garden. Design your garden so that you have some of these flowering plants close to your fruits and vegetables.

Organic Pesticides: Only as a Last Resort!

Sometimes even in a healthy garden, a pest population will explode. If you decide there is no alternative to using a pesticide, choose the least toxic organic one that will do the job. Remember that even organic pesticides will kill beneficial insects and pollinators along with pests, which is never a good thing. Organic pesticides, like all other ones, require careful handling to prevent skin irritation, and some, such as pyrethrum, can be toxic to pets and people if not used correctly. Some can make birds sick. The first step in applying an organic pesticide is to read the label thoroughly! Wear gloves and long sleeves, long pants, and shoes to lessen the possibility of contact with the skin, which may cause irritation. Shower off and wash your clothes immediately after you apply any pesticide.

Check the label to make sure the product is effective against the target pest or disease. Look for an Organic Materials Review Institute (OMRI) registration or the US Department of Agriculture (USDA) organic logo to make sure it is safe for organic gardens and the environment at large. Follow the label instructions to the letter. Applying pesticides inappropriately or too often not only will harm beneficial insects but also may create resistance in the pest population you are targeting. Inappropriate application may also harm the plants you are trying to save. For example, summer oil (horticultural oil) will burn plants if applied in hot, sunny weather; peppers and basil seem to be very susceptible to being burned, so wait until late in the day, when temperatures cool off, to spray them.

Pollinators, including honeybees, are extremely sensitive to chemicals of all types. Wait to apply pesticides until after dusk, when honeybees have gone home to their hives and are no longer foraging on the flowers. Choose, too, a calm evening when no rain is expected. Even a gentle breeze can carry pesticide drift to unintended areas. Target or spot-treat only where the pest problem exists.

Pesticides, organic or otherwise, should not be applied near or over ponds, ditches, streams, container fountains, or other water sources. Many formulas are highly toxic to fish, turtles, salamanders, and other aquatic organisms. Water often carries pesticides to unintended areas of the landscape, or even into the greater environment. There are few, but important, exceptions to this rule. A special formulation of Bt (Bacillus thuringiensis subsp. israelensis) that affects only mosquito larvae is an excellent tool, especially for gardens that contain a pond, fountain, or rain barrel. This biological larvicide is applied directly to standing water in containers. Killing off the larvae helps reduce the mosquito population, thus helping prevent the spread of diseases such as the West Nile virus.

More about garden health: Read another excerpt from The Wildlife-Friendly Vegetable Gardener in How to Build a Healthy Soil Community.


Excerpted from(c) Tammi Hartung, illustrations (c) Holly Ward Bimba used with permission from Storey Publishing. Purchase this book from our store: The Wildlife-Friendly Vegetable Gardener.