A: If we set a thief to catch a thief, then why not set a bug to eat a bug? Sometimes the best way to control an outbreak of an insect pest is to use another insect, or a close relative (such as spiders). Ladybugs, the most famous of these insect killers, are wimps compared to some of the other predatory critters in your garden. Lacewing larvae, ground beetles, praying mantises, wasps, hover flies, spiders… there are plenty of beasties who are more than happy to keep garden pests under control.
Most beneficial insects are already present in our yards, but we can increase their numbers by providing for their other needs. For example, adult lacewings (right) often delicately perch on flat-topped flowers such as Queen Anne’s Lace and blooming cilantro, sipping nectar. These adults then lay eggs, which hatch into predatory larvae—the insect equivalent of the Incredible Hulk!
Praying Mantises prefer warmer climates, but we do have several species here in Colorado. They overwinter as eggs, so you might find their egg cases (shown below) as you do your fall clean-up. (You can also populate your garden from egg cases purchased in the spring from a garden center or catalog.)
Indiscriminate killers, mantises will attack anything small enough to be captured, including both harmful and beneficial insects, small lizards, frogs, baby rodents, and even other mantises. (Mantises in other parts of the world grow much larger than the ones here in the U.S.!)
Wasps are another incredibly efficient means of biological pest control. Why would we want more wasps in our gardens? Most people think of paper wasps and hornets (which do eat other insects, by the way) or yellow jackets—the kind of wasps that sting us. But the wasps that patrol our gardens are tiny, parasitic insects that can be as small as 1/100 of an inch and are not at all aggressive. You probably won’t even notice them.
These wasps are the stuff of caterpillar nightmares. They lay their eggs in the soft tissues of their target prey. The wasp larvae then slowly eat their way out, killing the host in the process. If you discover an insect infestation that includes a large number of dark, dead, mummified bugs, don’t spray! Those dead insects have been killed by wasp larvae, and you don’t want to kill your helpers.
Most of these wasps are species-specific. That means that each kind of wasp has a particular insect that it parasitizes. If you decide to purchase parasitic wasps, it’s important to properly identify the pest so you know which species of wasp to get. Identifying insects can be very difficult; if you get stuck, your local master gardeners can be a big help.
Many of us are not big fans of spiders in our homes, but their value in the garden is undeniable. All spiders are predators!
Not all insectivores are other arthropods (segmented animals with jointed legs and an exoskeleton). Many vertebrates eat insects as well. Toads, lizards and snakes, some birds and rodents… all can play a part in natural pest control. For example, 2/3 of the diet of a Western Bluebird, shown here, is made up of insects and other invertebrates.
If you’re a fastidious gardener, you might be frustrated by using living pest-eaters. They won’t eat every single “bad bug” in your yard. Rather, the populations of prey and predator eventually reach a balance, with neither one getting the upper hand.
It’s also important to avoid indiscriminate spraying of chemical pesticides that not only eliminate prey, but also kill the very creatures you’re trying to encourage. If chemicals become necessary, check with a county extension agent for options that are more selective in their target species.
For more information on beneficial insects, check out CSU’s Fact Sheet, “Beneficial Insects and Other Arthropods,” by W.S. Cranshaw, who also took the above photo of the mantis egg case.
The photo of a Aleiodes indiscretus wasp parasitizing a gypsy moth caterpillar is courtesy of Scott Bauer, USDA Agricultural Research Service, Bugwood.org.
Article and other photos by Leslie Holzmann, Certified Colorado Gardener.