Download a pdf version of this page here: Beneficial Insects of the Willamette Valley
Assassin bugs have long, flat bodies, and usually an enlarged, flat area on the lower part of the hind legs. They catch other insects and impale them with their long, straw-like mouth, that they keep tucked under their body when they aren’t eating.
Carabid/Ground Beetles are nocturnal predators of soft-bodied insects like cutworms and cranefly larvae, snails and slugs, and insect eggs. They hide under bark or stones, or burrow into the ground during the day. If you uncover one, just let it go and it will burrow back down somewhere else. The larvae look like long, black or dark brown mealworms. they are also good nocturnal hunters. The picture shows the large one most people know, but there are dozens of others here of different sizes. They all are fast-moving, brown or black beetles with a shiny shell.
Centipedes are easy to tell apart from millipedes once you know what to look for. Centipedes have a flat profile, are usually red/brown or tan, and have one pair of long legs per large segment, projecting mostly sideways. They have venomous claws on their front segment, but they are too small to hurt humans around here (there are bigger tropical centipedes that can give a nasty sting, though). They are fast runners, so they’ll probably be well out of your way by the time you notice them. They like to hide in moist cracks and crevices, so leave an old log or two around the edge of your garden for them to live under, or plant trees with craggy bark.
Devil’s Coach Horse
Devil’s Coach Horse is a type of Rove Beetle with long, strong pinching jaws. They are great predators. They can theoretically give you a bit of a nip, but they will be more interested in getting away than biting. They look a bit like carabid beetle larvae, but you can see the short wing covers at the top of the abdomen that show that these are adult insects.
Earwigs get a bad rap. They are opportunistic predators who love to eat mites, nematodes, aphids, and mealybugs, and they also feed on decaying plant material. They rarely eat live plant material. If you find one in a damaged part of your plant, they are probably cleaning up after a slug of snail did the damage. They are also one of the few maternal insects, tending a nest of eggs and babies until their first molt. So leave the earwigs alone to eat your aphids and mites, and leave a few pulled weeds in piles for them to snack on.
Hover flies/syrphid flies have bright yellow stripes that make them look like a little wasp, but they can’t sting at all. You can identify them by their perfect hovering in front of the flowers they like to eat pollen from. They are great pollinators as an adult, and the larvae eat lots of aphids – sometimes as fast as one a minute. They look like tiny green maggots, which I guess they are, since they are true flies. The adult will find a patch of aphids and lay an egg in among them. The larva hatches out is a couple of days and starts chomping away. If you see a patch of just aphid husks on a plant, it was probably a syrphid fly larva. The adults especially like plants with tiny flowers like parsley, Queen Ann’s lace, and herbs.
Lacewings are easy to recognize by their pale green body (some are light brown) and long, clear, lacy wings, and they LOVE to eat aphids. The larvae look sort of like tiny alligators with long pinchers and eat anything they can find. They lay their eggs on long stalks to keep them away from other insects. Since they also like nectar, planting sunflowers, angelica, and even letting some of those weeds go to flower will attract them.
Everyone knows ladybugs, but their larvae eat even more aphids, and you should know what they look like so you don’t accidentally harm them. They are very obvious by their orange and black markings and spiky texture. If you find one while weeding, relocate it to a patch of aphids and it will clear them out.
Leatherwings, aka soldier beetles, have a long, straight body with dull black, leathery wings, a red head, and long antennae. They eat more aphids than a lady bug and range around more. The adults usually show up right about the first of May around here. The larvae live under bark on the ground or under leaf litter and eat lots of insect eggs, so don’t be too quick to rake up those leaves in the fall.
Predatory mites look a lot like a red spider mite, but are lighter colored and move faster (They also have longer legs and a smoother body if you really squint). They hunt down spider mites, thrips, and other tiny pests. Grow plants that make plenty of pollen to attract them. They also prefer damp conditions, so dense foliage helps keep them around.
You can tell they’re a fly from the single pair of wings and short, stubby antennae. They have a furry face and a long, tapering body, sort of like a tiny, murderous ice cream cone. They use their super large eyes to find other flying insects and drop down on them from above, where they can’t reach to defend themselves. Then they hold on tight and start sucking. They love to eat other types of flies, particularly houseflies, but I’ve also seen them eat bees. The larvae like to live in rotting wood, so an old log or stump on the property will give them a place to reproduce.
Hover flies/syrphid flies have bright yellow stripes that make them look like a little wasp, but they can’t sting at all. You can identify them by their perfect hovering in front of the flowers they like to eat pollen from. They are great pollinators as an adult, and the larvae eat lots of aphids – sometimes as fast as one a minute. The adults especially like plants with tiny flowers like parsley, Queen Ann’s lace, and herbs.
Leafcutter Bees are one of our 400+ types of native bees and are excellent pollinators. They look like mini honey bees. They are solitary nesters in old beetle holes or other cavities and cap off their egg/larval cells with leaves cut from alfalfa, clover, or roses. Damage to roses is minimal and well worth the extra pollination from having these guys around. They LOVE sunflowers, and while the females sleep in the nesting tunnels, the males sleep outside, and you can often find them still asleep in the morning on your sunflowers if you plant them.
Mason Bees or Orchard Bees are excellent pollinators of fruit trees in particular. The are solitary bees that seal off their larval cells with mud. You can buy mason bee larvae to get started, but they are generally around in any case. To keep them, you can buy mason bee blocks or paper straws for them to nest in, or drill 5/16” diameter holes at least 3 inches long into a solid block of wood, or rout out 5/16” channels in boards and stack them to make tunnels. Set them out or hang them in a protected place with south or west exposure. Local mason bees will find the holes and move in.
Earwigs get a bad rap. They are opportunistic predators who love to eat mites, nematodes, aphids, and mealybugs, and they also feed on decaying plant material. They rarely eat live plant material. They are also one of the few maternal insects, tending a nest of eggs and babies until their first molt. So leave the earwigs alone to eat your aphids and mites, and leave a few pulled weeds in piles for them to snack on.
Millipedes have a rounder profile and are MUCH slower than centipedes. They also have 2 pairs of fairly short, thin legs per short segment. Instead of running away, they tend to curl up in a protective spiral when disturbed. They are primary decomposers and only eat rotting vegetation. They will not harm any living plants. They tend to be small and gray around here, but there are very large, shiny black millipedes with bright yellow or orange spots on their sides in our coastal and cascade range forests.
Pill bugs are like many-legged armadillos. They roll up into a ball for protection when disturbed. They are everywhere there is good soil with lots of organic material. They are primary decomposers and eat ONLY dead plant material.
Adult soldier flies do not eat. They look a lot like wasps, but can’t bite or sting and are completely harmless. To accentuate the wasp look, they have clear “windows” at the front of their abdomen. When they fly, light shining through them gives them a long-waisted wasp look. The larvae are some of the very best composters and will turn scraps into good rich compost in a hurry. The larvae are also prized as fishing bait.
Sowbugs look a lot like pillbugs, but are flatter and can’t roll into a ball. They are also primary decomposers and won’t harm any live plants. Essential for your compost pile.