Frogs and toads can be formidable predators of insect pests. (Photo: Norio Nomura/Flickr)
When you grow plants for food, you're part of a cultural revolution that dates back more than 10,000 years. It might not seem very revolutionary today, but agriculture helped our hunting-and-gathering ancestors sow the seeds of civilization. It was almost like humanity had finally begun to wean itself off the wilderness.
As much as agriculture has changed us, however, that last part never happened. We're still woven into the wilderness, which gives us food, resources and other ecosystem services. It also gives us pests, though, which sometimes overshadow all the potential allies that share our habitats. Fences and various deterrents can help defend farms and gardens from wildlife, but so can other wildlife — if we let it.
Growing food isn't about green-thumbing our nose at Mother Nature; it's about knowing her well enough to enlist her assistance. For home gardeners, that often means avoiding broad-spectrum pesticides, since they tend to kill more than just pests. But it doesn't necessarily mean leaving our gardens unguarded. On top of defensive measures like fencing, traps or repellents, wise gardeners cultivate not only crops, but also a habitat for wildlife that naturally keeps pests in check.
To fully embrace this approach, you may want to explore the big-picture ideas of biodynamic agriculture and integrated pest management (IPM), and to encourage pollinators as well as predators and parasites. It's also worth noting the animals in this list are not panaceas, and depending on species and context, some can even be pests. For a primer on their potential benefits, though, here are a few examples of creatures that can help you guard your garden with free, nontoxic pest control:
Weaver ants can not only protect tree crops from pests, but may also improve the quality of produce. (Photo: Rushen/Flickr)
Many ants are farmers themselves, having raised crops and livestock for millions of years. That won't compel them to help us — some species herd crop pests like aphids, for instance — but it does illustrate how complex and influential ants can be.
Not only do ants offer indirect benefits like making and aerating soil (which is more important than it might sound), but they can also fend off an array of more irksome insects. Research suggests certain ants control crop pests at least as effectively as pesticides; in one study, cashew trees guarded by weaver ants had 49 percent higher yields than pesticide-treated trees, and also produced higher-quality cashews, bringing farmers a 71 percent higher net income. Ants have also been found to rival chemical pesticides in protecting crops such as mango, cocoa and citrus.
Many bats offer free pest control, eating hundreds or thousands of winged insects per night. (Photo: Andy Kainz/Flickr)
Summer evenings are often a great time to work in your garden, although mosquitoes can quickly put a damper on crepuscular cultivation. It's pretty hard to focus on gardening while you're fending off hordes of bloodthirsty flies.
Fortunately, some local wildlife may be happy to help. Just one little brown bat, for example, can eat hundreds of mosquito-sized flies in a single night. Insect-eating bats may not be a silver bullet — it's still unclear how much they can suppress mosquito populations on their own — but as a 2018 study found, certain species (namely the little brown bat) really are prolific predators of mosquitoes.
And that's not all. Aside from mosquitoes, insect-eating bats also eat many moths whose caterpillars directly threaten crops. Just by eating corn earworm moths, for instance, bats save U.S. corn farmers roughly $1 billion every year. (And, like bees and butterflies, some fruit-eating bats are also important pollinators.) If you'd like to enjoy the benefits of bats, consider these tips for attracting and housing them.
Birds, like most animals on this list, are not easily pigeonholed. While some tend to run afoul of farmers — hence the ancient tradition of making scarecrows, for example — avian visitors often thanklessly protect our farms and gardens.
Lots of songbirds prey on crop pests like caterpillars, beetles, snails and slugs, especially when they have hungry mouths to feed in breeding season. Many offer tangible benefits to people, such as reducing leafhopper abundance by 50 percent in vineyards, cutting caterpillar damage in half at apple orchards or saving coffee farmers up to $310 per hectare by eating borer beetles, to name a few.
To lure more songbirds, it helps to know which insect-eaters live nearby and what they look for in a habitat. (Talk with local growers, check field guides, and try resources like the Cornell Lab of Ornithology, the U.S. National Audubon Society or the U.K. Royal Society for the Protection of Birds.) Native trees and shrubs can be a big draw, potentially tripling bird diversity in agricultural areas, although some birds are picky about things like tree type, height, foliage and distance from water.
Birds of prey
Songbirds may eat insects, but what about bigger pests like squirrels, rabbits, rats or moles? Or what if songbirds are raiding your garden instead of protecting it? To battle these bulkier bandits, many people simply befriend a different kind of bird.
Raptors, aka birds of prey, include a variety of predators like falcons, hawks and owls. Many species hunt precisely the varmints that covet our crops, sometimes even providing a clear boost to yields and profits. The key is identifying your pest, knowing your local raptors and finding the best bird for the job. If rabbits eat your kale after dark, for example, you might want to attract nocturnal owls, but if squirrels nab your tomatoes in broad daylight, the answer may be a falcon or hawk.
Some raptors are also better-suited to certain environments. A family of barn owls can eat 3,000 rodents in one four-month breeding cycle, but they prefer larger properties with open space for hunting. You could set up a nest box for them (or more than one, since they aren't territorial), or target a different species like barred owls, forest dwellers that also prowl wooded suburban areas. Not all raptors are receptive to next boxes, though, so first check with a group like the Raptor Resource Project, the Raptor Institute, the Hungry Owl Project or the Barn Owl Trust.
Dragonflies and damselflies
Dragonflies hunt a variety of garden pests; this one appears to be eating a spittlebug. (Photo: L Church/Flickr)
Dragonflies and damselflies are expert aerial hunters, nabbing prey from midair with a success rate as high as 95 percent. They are especially beloved for feasting on mosquitoes, midges and gnats, a service that can make it much easier to spend quality time in your garden or other outdoor spaces during the summer.
These acrobatic hunters are also known to prey on adult moths and butterflies. That may be cold comfort if caterpillars are already eating your crops, but dragonflies and damselflies are still part of an IPM approach, or "an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques," according to University of California Cooperative Extension.
If you want to attract dragonflies and damselflies to your property, having a pond or other water feature is a significant plus. For more suggestions, check out this guide on how to create a dragonfly garden.
Frogs, toads and salamanders
Native amphibians can be a blessing for farmers and gardeners. That includes frogs, toads and salamanders, most of which are opportunistic insectivores.
As generalist predators, these amphibians may eat some beneficial insects like ladybugs, lacewings or dragonflies. Yet herbivores often make easier prey, and since a single frog or toad may eat up to 100 insects per night, any crowds of leaf-eating pests in your garden would make a tempting feast. Frogs and toads devour all kinds of beetles, flies, moths, caterpillars and other insect larvae, as well as slugs and snails, providing a powerful check on garden thieves. Salamanders have similar diets, ranging from herbivores to disease vectors like mosquitoes and ticks.
The key to attracting amphibians is to create a suitable habitat for them. That includes foliage and other cover from predators, sources of moisture and shade, and possibly a small pond (especially for frogs). It may also include a toad house or frog house, which can be as simple as an overturned flower pot to provide a cool, moist place to hide. And due to amphibians' permeable skin, they're highly sensitive to pesticides and pollutants, so toxic chemicals should be avoided.
Ladybugs, also known as lady beetles or ladybird beetles, are some of the most famously beneficial garden insects. They're beloved not just for their iconic appearance, but also for preying on aphids, scale insects, leafhoppers, mites and other crop pests. Some ladybugs can behave as pests themselves, either by damaging crops or outcompeting native species, but overall these beetles are valuable allies. Just one ladybug can eat as many as 5,000 aphids during its life.
It's possible to buy kits of ladybugs to release in your garden, and while that may be fine, it's generally best to encourage existing wildlife rather than trying to start a local population from scratch. As with most beneficial wildlife, your garden should be free of insecticides that could harm helpful insects like ladybugs. It should also have aphids or other insects for them to eat, although that's presumably why you want ladybugs in the first place. And, since many ladybug species eat nectar and pollen as well as insects, it can help to grow plants whose pollen is popular with ladybugs.
For examples of those plants, along with other suggestions, check out this guide on attracting ladybugs to your garden.
Like ladybugs, green lacewings are important predators of soft-bodied insects and insect eggs, according to University of Kentucky entomologist Ric Bessin, who writes that, while underappreciated, "their contribution to insect control is immense."
Unlike ladybugs, however, green lacewings are not carnivores at all life stages. While both ladybug larvae and adults feast on aphids and other insects, green lacewings often shift from a larval diet of insects to an adult diet of nectar, pollen and honeydew. The adults of some lacewing species do still eat insects, Bessin notes, but otherwise their main role in pest control is producing more carnivorous larvae.
And those larvae are no joke. Also known as "aphid lions" or "aphid wolves," they ravenously attack aphids and other soft-bodied insects with their large mandibles (pictured above). One lacewing larva can eat as many as 200 aphids per week, and may even cannibalize its fellow larvae if there isn't enough prey available.
To host aphid lions, you'll need a space that impresses their parents. Green lacewings are attracted to certain garden plants, according to the Permaculture Research Institute, including caraway, coriander, dandelion, dill, fennel, four-wing saltbrush, golden marguerite, prairie sunflower, purple poppy mallow and Queen Anne's lace. Of course, you'll also need to tolerate a few aphids or mites for the larvae to eat.
Snakes, lizards and turtles
Snakes have a knack for scaring people, making it hard for some gardeners to accept them as allies. Most snakes aren't venomous, though, and even those that are mainly use venom to subdue prey, not for self-defense. It may still be unwise to welcome venomous snakes into your garden, but it wouldn't be wise to simply banish all snakes, either. Most snakes are not only harmless to humans, but also helpful in controlling pests that actually do cause us trouble. (For help with identification, check out this guide to distinguishing venomous and non-venomous snakes.)
Garter snakes, for example, are known to prey on crop-damaging herbivores like slugs, snails and grasshoppers, as well as larger pests like rodents. As with many other animals in this list, the key to attracting beneficial snakes is to offer them a suitable habitat with shelter, a water source and minimal toxic chemicals.
If you just can't tolerate snakes, some other reptiles fill a similar ecological role. Many lizards, for example, feed on slugs, snails, and leaf-munching insects like beetles, caterpillars and grasshoppers. There are a few venomous lizard species, but the vast majority of lizards found in gardens pose no threat to people (or plants). Turtles have wide-ranging diets that may be largely vegetarian, but certain types — like North American box turtles — also eat garden pests such as snails, slugs and beetles.
Like bats and snakes, spiders are unfairly typecast as scary. They rarely bite people, and even when they do, most bites are only minor nuisances. Their venom is meant for much smaller prey, including insects that cause more trouble than any arachnid. House spiders patrol our homes for pests like flies, mosquitoes, fleas and roaches, and outdoor spiders can play even more valuable roles in farms and gardens.
Your friendly neighborhood spiders come in several basic forms, each with its own pest-control superpowers. A wide array of web-weaving spiders, for example, set silky traps to ensnare aerial prey such as beetles, flies, mosquitoes and moths. (In North America, one well-known example is the iconic black-and-yellow garden spider.) Many crab spiders also sit and wait for prey, but instead of weaving a web, often hide amid flowers until an unsuspecting insect shows up to be ambushed.
Some wolf spiders also rely on ambush hunting, but these robust arachnids are best-known for roaming around in search of prey, which can make them especially helpful for farmers and gardeners. That's also true for jumping spiders, impressive hunters armed with excellent vision and vibration-sensing abilities. Some use surprisingly sophisticated hunting tactics, such as taking indirect routes to avoid being seen, that have drawn comparisons to big cats. They can have a significant effect on crop pests, but as with many spiders, they may not respond well to pesticides.
Braconid wasps are a nightmare for many pest insects like aphids, beetles, flies and caterpillars. (Photo: Katja Schulz/Flickr)
Wasps are a diverse group of insects, with some offering more perks than others. Many predatory wasps actively hunt crop pests, but like other generalist predators in this list, they can prey on beneficial insects, too, including bees. That doesn't necessarily outweigh their benefits, but since some social wasps aggressively defend their nest, a lot depends on species and setting. A few predatory wasps could help, but a yellow-jacket nest among your crops is likely more trouble than it's worth.
There are also other wasps, however, that offer a subtler form of pest control without the threat of painful stings. Known as parasitoid wasps, these are highly diverse insects that often target specific garden pests as hosts for their offspring. Some use incredible tactics to find and control hosts, such as sniffing out chemicals in their feces or injecting a virus to weaken their immune systems. Certain parasitoid wasps are used as biological-control agents to combat major agricultural pests.
One such pest is the tomato hornworm, a large and voracious caterpillar that can defoliate tomato plants with alarming speed. Hornworms are a popular host for some parasitoid wasps, which inject their eggs into the caterpillar and then fly away, leaving behind a brood to hatch inside the live host. The eggs soon release little wasp larvae, which feed on the hornworm until they're ready to pupate. The larvae then form visible cocoons outside the host's body (pictured above).
The hornworm is still alive at this point, and may continue walking around, but it has stopped eating. In fact, if you see a hornworm covered in tiny cocoons like this, the best way to protect your garden is to just leave it alone. Once the adult wasps emerge, they'll kill the host and patrol the area for other hornworms.