Natural Pest Control for Gardeners and Landscapers: It's a Bug-eat-Bug World

The no-work, pesticide-free approach to controlling garden pests is to let their natural enemies eat them. The easiest and cheapest way to minimize the numbers of insects that damage your plants is to encourage predator insects that will eat the plant-damaging insects for free. The easiest and cheapest way to encourage these insect predators is to stop killing them - stop using pesticides in the garden. There may be a brief surge in the plant eaters, but the predator populations will expand to control them.

Caterpillar on 4 O'Clock Flowers

Think of the advantages for you - no buying pesticides, no weekends wasted spraying pesticides, not worries about pesticide residues on your vegetables. Just sit back and watch the food chain in action. For sex, violence and mayhem, it matches anything you can find on television, except maybe Game of Thrones.

Ladybugs and Lacewings
The familiar glossy red ladybug and the delicate golden-eyed lacewing species are voracious aphid eaters as larvae and adults. I don't bother buying ladybugs at the nursery because aphid-infested plants give off a chemical that attracts ladybugs.
If you panic at the sight of aphids and spray them with pesticides, you will never have enough aphids to keep ladybug and lacewing babies alive. If you accept that there will be hordes of aphids on a couple of plants for a week or so, the predators will arrive and lay their eggs on the food source. A week or so after that, the aphids will be under control.
Both ladybugs and lacewing adults eat pollen and nectar, so be sure to have something blooming for them.

Mud Daubers and Other Predatory Wasps
Mud daubers are solitary hunting wasps, and their favorite prey is large spiders, giving them the local name of "tarantula hawk". I often see them running under pots and into the lizard shelters, looking for black widows. They sting the spider to paralyze it, then haul it to their nest to feed their young. The nests are mud blobs, or elegantly shaped mud vases, stuck to walls in shaded spots. To attract mud daubers, all you need is a muddy spot they can gather nest material from and some insect prey.
Other predatory wasps, such as yellowjackets and hornets, hunt caterpillars. Some are solitary burrowers, others are communal "paper wasps" that build their nests under eaves. The risk of being stung is minor even if the nest is dangling from your front porch's ceiling.

Paper wasp and her new nest (one of the Polistes species)

"Velvet ants" are actually a species of wingless burrowing wasp, covered in bright orange, red, or yellow hairs. They hunt on the ground, and will sting if you grab them, but they will run right over your bare feet without stinging.

Any wasp has a nasty, painful sting. I have been stung once by a mud dauber and once by a velvet ant (my fault both times). It hurt. It really hurt! It was pound your head on the wall in hopes of knocking yourself out kind of hurting for a couple of hours. However, they are not aggressive unless you bother them or their nest, and their pest-control value outweighs the tiny risk of being stung.

Syrphid Flies: Predatory Infants, Vegetarian Adults
Syrphid flies, commonly called "hover flies" are a group of related species that look like small bees or wasps, but their flight pattern identifies them - they hover and dart in all directions. Many of the species are predators as larvae, and eat pollen or nectar as adults. They are stingless.

They lay their eggs on aphid-infested plants, or on plants close to the infested plants. Their babies are small legless creatures that look like a very tiny Jabba the Hutt. They eat hundreds of aphids as they grow, and may also eat small caterpillars, mites or other soft-bodied insects.

Adult syrphids are vegetarian, and can be encouraged to hang around by providing pollen and nectar sources for them. Shallow daisy-like flowers are their favorites. Mixing rows of flowers in with the vegetables in your garden would maximize their protective effect.

Preying Mantids
Some folk think that mantids eat too many other predators to be a desireable insect. They will eat any creature small enough to overpower, including other mantids, so you usually end up with one adult female per plant. I watched a mantis egg case hatch once. The first amazingly tiny litte mantis emerged and waited. Its first meal was the second tiny mantis that emerged. Mantis hatchlings were scattering in all directions, trying to catch and eat their siblings without being eaten themselves.

To encourage these, you need a population of tiny insects, such as aphids, for the infant mantids to eat. When you are pruning bushes in late summer, check the clippings for unhatched egg cases. Fasten them to plants that usually have aphid problems, one egg case per plant, and let them hatch out in the spring.

Spiders As Predators
All spiders are predators, but they don't seem to be very popular. People give me strange looks when I talk about useful spiders. Almost any spider has venom that will raise a painful itching lump on your skin, and most of them will bite if you disturb them, but no spider is going to hunt you down just to bite you. Given the opportunity, most of them will hide from you. Unless it's a known dangerous species in an area where someone is likely to be bitten by it, leave it alone.

The same habitat that keeps the reptiles safe from the cats has attracted several wolf spiders. Wolf spiders are long-legged, covered with short grey or brown hairs, and fast runners. Really fast runners. They are active at night, huinting crickets and cockroaches. There are also many "jumping spiders" hunting small insects. These are stocky little spiders, often brightly colored, that stalk their prey and then leap at it.

Black widows are the dominant dangerous species here, but they catch and eat crickets, and also are a source of food for the tarantula hawks. To discourage them, I try to keep the patio clean, sweep out their webs as I find them, and occasionally squash one. I don't deliberately seek and destroy them.

Predatory Ants
I never considered ants as serious hunters until I saw them swarming all over an army of caterpillars that were trying to devour a mesquite. I haven't a clue about how to attract them, but I leave their nests alone as much as possible.

Three kinds of ants can be pests:

Fire ants, of the imported Argentine kind, are a kill on sight kind of insect in the USA. The native desert fire ants are smaller, but leave itching painful welts. The seem to have telepathy, because they will swarm onto your hands or feet, then all bite at once.

Harvester ants gather seeds, which is not a problem. However, some species like to have their nests in the middle of a barren clearing, and will chew down vegetation to create the clearing. One ambitious nest in my front yard had a 3-foot bare spot chewed into the middle of a dense ground cover.

Leaf-cutter ants will cut chunks out of leaves and carry them back to their nest. If you have a large colony of them, they can leave nothing but a bunch of naked stems.