Drunken Slugs and Cozy Toads: Tips for Natural Garden Pest Control
May 23, 2019
Put down that chemical pesticide. You can create a non-toxic garden that supports its own defense system if you go all in and rely on biological warfare for natural garden pest control. Here's how to provide habitat and sustenance to beneficial critters, from single-celled fungi to furry flying mammals.
How to attract toads (and other amphibians) to your garden
If you have a garden pond or live near a slow-moving body of water, you probably have plenty of bug-eating frogs. But how about land-loving toads? All native amphibians will eat pretty much anything they can stuff into their faces. Here's some insight from the Cooperative Extension "Ask an Expert" service.
- Toads and their cousins can travel many miles to find their ideal habitat.
- Never relocate amphibians. This spreads amphibian diseases, and the animals will try to return to their old homes—often dying in the process.
- If you build a water feature accessible to frogs, toads, salamanders, and newts, don't keep fish in it. Amphibians avoid water where fish might eat their eggs.
Set up a "toad abode" in a shady, out-of-the-way spot: An upturned pot with a toad-sized doorway, either home-made or bought online, set firmly in damp, diggable soil works beautifully. Another approach is to hollow out a sloping burrow in the soil, place an untreated board or flat stone across the top, and pile on moss or groundcover plants. Wet down the surrounding area on hot days to keep the humidity up. If there isn't a good water source nearby, place (and refill daily) a large baking dish filled with clean water halfway into the soil. Toads don't drink water—they soak it up through their skin.
We suggest you set up a few toad houses around your garden to give them some options, and to create their own little neighborhood.
Build a bat house
North America is home to four bat families, further divided into more than 75 species of winged furballs. Some bats are pollinating specialists, while others devour crop-damaging and disease-spreading insect pests. The ubiquitous little brown bat, for example, can eat one insect every seven seconds while it's in hunting mode, and it loves cutworm and borer moths, flying termites and ants, and leafhoppers...not to mention mosquitoes. Larger bats will eat flying beetles, crickets and grasshoppers. A single bat can eat thousands of bugs each night.
Build a bat house with your kids, or buy one from a bat-savvy source. Bat Conservation & Management and Bat Conservation International are excellent resources for kits, plans, and ready-to-hang bat roosts, and keep these tips in mind as you scout out locations:
- Bats prefer to roost within 1/4 mile of riparian areas, where bugs congregate and breed.
- Choose a pole or sturdy dead tree that's at least 25 feet away from a densely-wooded area.
- Place the bat house 15 to 20 feet up.
- Make sure the entrance isn't blocked by plants or other obstructions.
- Place on the south or southeast side of the pole.
- Bats need 100 to 110°F daytime temperatures in their roosts to raise their young, but males appreciate slightly cooler homes.
- Be patient! It can take 12 to 18 months for bats to move in.
- Bats are sensitive to stains, paints, and wood treatments. Keep your bat house interiors chemical-free!
Check out these mugshots of the most common bats patrolling US airspace and try to deny that they're adorable. Just wait until you notice how few skeeters you have to slap each evening, and how incredibly healthy your garden looks—especially once you have a decent supply of high-phosphorus bat guano.
Last call! Use beer to bait snails and slugs
You've probably tried trapping snails and slugs in beer-filled containers. Maybe you caught a few, but not enough to make a dent in the population. Maybe you didn't know you have to set the traps no more than six feet apart; they attract slimers within a three-foot radius.
Instead of beer traps, use them as lures.
The yeast and sugar in beer draw in snails and slugs, so unless you're on a Natty Lite budget, it's cheaper to make your own brew. After dark, wet down an area near ideal slimer hangouts, which include low-growing, shady plants, debris piles, stone overhangs, and under flower pot dishes. Set out saucers filled with your homemade mixture, and go drink real beer for a couple of hours. When the temperatures cool off, the snails will gravitate towards the bait. Grab a flashlight and gloves, and go pluck 'em up.
You'll note that most of this article focuses on using live organisms to defeat garden pests. We're totally justifying this method by pointing out that yeast is, indeed, a living organism.
Invest in a beetle bank
"Ground beetle" is a generic name assigned to members of the Carabidae family, and they're excellent biological weapons in the war against insect pests. They specialize in assassinating ground-dwelling invertebrates and can eat the equivalent of their body weight in a single day. Here's some of their favorite food:
- Pest insect eggs
The vast majority of ground beetles are carnivores, but some eat weed seeds. In fact, research indicates ground beetles have an untapped potential for weed control, and Penn State University suggests there are far more weed-destroying ground beetles than we think.
When home gardeners or commercial growers create beetle-friendly habitats among their row crops and ornamentals, they're building beetle banks. The idea is to create an area that doesn't get soggy, has plenty of cover under which to hide, and provides access to the plants you want them to protect. These can be mounded earth or small, two-foot by four-foot raised beds planted with low-growing perennials.
Carabids lay their eggs just beneath the soil surface, or in the leaf litter and plant residues just above. They remain in the patch during their larval and pupal stages, the former spent entirely underground. So, it's essential to leave your beetle banks undisturbed and to cover them with plenty of leaves or straw mulch.
We'll bet you've already met a few ground beetles in your garden. Check out the above link to Penn State's page if you haven't already—you might recognize one or two of their featured species.
Attract or release predatory wasps
Trichogramma wasps are classified as egg parasitoids. Most of them are quite small—some as tiny as the dot on this i—but their size makes them deadly to their prey. They lay their eggs inside those laid by pest species, and as the wasp eggs hatch, the larvae devour the developing "host" larvae.
If that thought freaks you out, just wait: Trichogramma isn't a single species. It's the name we use to refer to members of the Trichogrammatidae family, which contains roughly 800 species among 90 genera. They're everywhere. They're evil. And they're on our side.
Trichogramma wasps will do serious damage to about 200 pest species, most notably these:
- Cabbage worms
- Codling moth larvae
- Diamondback moth larvae
- European corn borers
- Tomato hornworms
If you want to boost your beneficial wasp population, you can purchase parasitized moth eggs. These come glued to a square of card stock, which you suspend in a protected area in mid- to late spring (be sure there are at least a few plants in bloom). But why go through the hassle? You can grow some of their favorite blooming plants from seed to draw in adult Trichogramma wasps:
North Carolina State's Cooperative Extension places these wasps far, far above European honeybees and bumblebees in terms of pollination efficiency, and encourage gardeners to create consistent food sources to support their populations: "If you want to attract pollinating wasps to your garden, consider adding plants that flower year-round." Easy for you to say, North Carolina. You're so smug, down there with your 210+ day growing season.
Lure in—or let loose—green lacewings
As with ground beetles and Trichogramma wasps, green lacewings are a generic term applied to a large insect family, in this case, it's Chrysopidae. Adult lacewings are pale to medium green (some are brown) with bronze-colored eyes. Their long oval wings, which are about 130% of their entire body length (half to one inch), are transparent with delicate, lacy veins.
Some species will eat insects, but they mostly live off pollen, nectar, and aphid honeydew. In spite of their impressive wings, they don't fly very far from home base or fly much at all. That's probably a good thing if you have bats on the prowl—lacewings are nocturnal.
A single adult lacewing female will find substantial aphid populations and deposit 300 to 500 eggs nearby. The tiny white oval eggs hang from long threadlike stalks, very much resembling downsized and slightly bendy sewing pins.
Lacewings' peak performance happens during their two- to three-week larval stage when they're reverently called "aphid lions." Lacewing larvae are about a half-inch long and camouflaged in rusty brown, usually with cream bands and spots. This is to protect them from the ants that guard their aphid "milk cows," and from birds and other predators.
Lacewing larvae refine their Special Forces cred by decorating themselves with bits of leaves, dirt, and dandelion fluff. They think they look so hardcore! Even if we think they look like itty bitty Bichon Frise puppies, they truly are badass: Aphid lions can eat about 200 aphids during their larval stage, and they'll eagerly devour any other insect in its path. For some great lacewing close-ups, visit Insect Identification for the Casual Observer.
You can purchase lacewing eggs, larvae, and adults and release them according to instructions specific to the stage of life, but if you're happy to hold onto your money, entice lacewings by growing nectar-rich flowering plants, including those favored by beneficial wasps. Have aphids? You'll soon have aphid lions. Don't knock down minor infestations, since the adults will leave without a food source. Plants grown from healthy genetics should tolerate a few aphids now and again.
What about ladybugs and praying mantids?
What about them?
Nah, they're great. At least, they're cute. But neither is as effective as the species featured above nor are they as economical for natural garden pest control. We're more interested in naturally attracting pest predators than taping dollar bills to their backs and waving "buh-bye."
But we're we, and you're you. If you want more info on ladybugs and praying mantids, then who are we to deny our lovely readers? Check out this great article about releasing ladybugs for aphid control from the wonderful University of California agriculture nerds. As for praying mantids, the University of Wisconsin-Madison doesn't consider them to be worthy of the beneficial insect or biological control organism titles.