Beneficial insects Gardening Harmful insects

Bugs: Garden Friends or Foes?

Garden soil isn’t sterile … and we wouldn’t want it to be sterile. Rather, it needs to teem with life. Mostly microbial life, too small for our eyes to see: fungi, bacteria, nematodes, etc. But also, small creatures we can see. We’ll call them “bugs” here, a sort of colloquial term that covers any little creepy-crawly animal. So, by our definition, bugs can include insects and other arthropods, but also gastropods, worms, etc.

Some gardeners seem to adopt the attitude that if it moves, you should squash it. But not all of these small creatures are harmful. In fact, according to some studies, only 1 to 3% of the “bugs” you run into while gardening could actually be seen as enemies in any way. Instead, many are simply inoffensive. But about as many are actually useful.

 There’s a whole range of helpful critters that take on a lot of roles—pest control, organic matter decomposition, soil aeration, flower pollination, and so on—and which are therefore beneficial. Or at least inoffensive. The creatures that attack our plants, eating leaves, roots or flowers, for example, and are therefore harmful, are comparatively few.

But how do you tell the good guys from the bad guys?

Well, the only way to do that is to learn a bit more about them!

20 Portraits of Our Plants’ Friends and Foes

Here are 20 examples of “bugs” that you may see in your garden, as well as a rating as to whether they are beneficial or harmful.

And be forewarned, some of the information may surprise you!

Ants

Ant on peony bud
Peony flower buds produce nectar to attract ants so the latter can protect them against their predators. Photo: serkucher, depositphotos

There are more than 1,000 species of ants in North America alone…. And most are harmless. They are above all detritivores: scavengers of dead organic material, especially plant detritus. That means they are beneficial. Also, many are predators of several plant enemies.

However, certain species harm plants by farming aphids on them. Yes, they literally raise them for the sweet honeydew they produce and even protect them by chasing away beneficial insects. Sometimes the same ants even transport aphids from plant to plant, spreading the infestation.

For other species, it’s the ant nest (anthill) that can damage lawns and gardens when it shows up in the wrong place. And carpenter ants, although highly beneficial in the wild because they decompose dead wood, are very harmful when they attack our wooden constructions.

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Rating: Generally beneficial, but sometimes harmful


Bees

Honeybee on yellow flower.
Honeybee. Photo: prudek, depositphotos

Honeybee. Photo: prudek, depositphotos

Often striped black and yellow, bees come in all sorts of sizes. They’re generally plumper than their cousins, the wasps. And often hairier too. In particular, they’re important pollinators of our plants. Without bees, there will be no apples, squash, or many other common human foods. True enough, some can sting (although not all). However, bees are not aggressive. If you leave them alone and don’t get too close to their nest, bees won’t bother you.


Rating: Beneficial

Butterflies

Black swallowtail butterfly on zinnia.
Black swallowtail butterfly: the adult is beautiful, but the larva eats our vegetables (celery, carrots, parsley, etc.). Photo: okiepony, depositphotos

There are thousands of species of butterflies, so necessarily this comment will be a bit of a generalization. However, adults tend to be important flower pollinators. Also, on the beneficial side, gardeners generally like to see the more colorful butterflies fluttering around their yards, so I give them extra points for making our lives happier. However, butterfly larvae (caterpillars) feed on plants, including garden plants. Among the varied types of caterpillars, cutworms cause a lot of damage to vegetables, cabbage worms devour the leaves of our cabbages and other brassicas and the huge tomato hornworm quickly defoliate tomato plants. And those were just a few examples.

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Rating: Those whose larvae feed only on weeds are clearly beneficial, but others are both beneficial and harmful.


Centipede

Centipede.
Centipede. Photo: Valentin Ayupov, depositphotos

Centipedes are long, fast-moving, wormlike, segmented arthropods with fairly long legs and antennae. They are best told apart from their distant cousins, millipedes, by the fact they have one pair of legs per segment…. and move faster! The number of segments varies by species, but many common centipedes have 15 segments, much less than millipedes. Centipedes are nocturnal predators of pest insects and slugs. The centipede theoretically has a slightly poisonous bite, but it rarely penetrates the skin of humans.


Rating: Beneficial


Earthworm

Earthworm.
Earthworm. Photo: ppl1958, depositphotos

This long tubular creature, with a soft body and no legs or eyes, is essentially a detritivore. It decomposes plant waste and makes it accessible to plants. And it aerates the soil with its tunnels. Again, a benefit for gardeners. So, all is good, right?

Well, not so fast.

In most of North America, there were no earthworms until Europeans brought them over from their native lands. Earthworms are now expanding and wreaking havoc in natural environments, as North American natural landscapes evolved without their presence. For example, they damage forests, because they excessively reduce the depth of leaf litter, leaving tree roots exposed that never evolved to face exposition. (Never release earthworms into a forest after a fishing trip: the result can be an environmental disaster!) They do similar damage in prairies, seriously reducing the thatch native grasses need.

One minor point: some gardeners also object to the castings (small clumps of excrement) that the earthworm leaves on the lawn. They claim they make their lawn lumpy. In fact, though, castings are beneficial to lawns because they are so rich in minerals.

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Rating: beneficial in man-made gardens; harmful in natural environments, at least in North America.


Ground Beetle

Ground Beetle.
Ground beetle. Photo: Bernard Dupont, Wikimedia Commons

Fairly large crawling beetles that gardeners run into when digging and weeding in the garden. They are usually black or metallic in color. They are quite active and try to hide when discovered. Many people squash them without thinking much about it, but in fact they are predators, consuming our gardens’ enemies, such as slugs and aphids, and do no harm to plants.


Rating: Beneficial


Hoverfly

Hoverfly
Hoverfly resting on a flower. Photo: Denis Vesely, depositphotos

The hoverfly is a fly that zips from flower to flower like a bee. Moreover, it often masquerades as a bee, copying its colors. That way it can protect itself from predators who often fear and avoid bees.

As the name suggests, a hoverfly is capable to hovering (remaining in one place in the air). It’s an outstanding pollinator and, just as important, the larvae of several species are formidable predators of harmful insects, in particular aphids. Having no stinger or sharp mouth parts, the hoverfly is harmless to humans.

It’s easily distinguished from bees by its huge eyes which seem to take up almost its entire head!


Rating: Beneficial.


Lacewing

Green lacewing
Green lacewing. Photo: Alex Kharkov, depositphotos

An attractive insect ½ to ¾ inches (10 to 15 mm) long, usually pale green, with transparent membranous wings with green veins. It’s a voracious predator of aphids, spider mites and other enemies of our plants. The larvae too, although much less attractive, are important predators of harmful insects. You can buy lacewings for release in your garden.


Rating: Beneficial


Ladybug

Orange ladybug with black spots.
Ladybug. Photo: Taden1, depositphotos

We have been taught since kindergarten that the little dome-shaped insect with polka dots on a red-to-orange background is beneficial. And that it eats the aphids that harm our vegetables and other plants. As a result, the ladybug (or lady bird) is one of the rare insects most people know as being a “good bug”. So, generally, they leave them be.

It can be useful to look into the appearance of a ladybug larva, because it looks nothing like the adult and you might confuse it with a pest. And the larva is just as greedy a predator of harmful insects as the adult!


Rating: Beneficial


Asian Ladybug

Different color phases of Asian ladybug.
The Asian ladybug is very variable in color: red, orange, yellow, black, with a changeable number of spots. It also goes under the name harlequin lady bug. Photo: Hedwig Storch, Wikimedia Commons

This species is more problematic, at least outside its native Asia. It’s an imported ladybug, introduced to Europe, North America and elsewhere as a predator of aphids and other pests. And yes, it is beneficial during the summer. After all, it’s just as voracious as any other ladybug in suppressing pests.


It isn’t nearly as desirable in the fall, however, when it moves into homes in large numbers to escape the cold. Also, it tends to replace native ladybugs in the wild, some of which are now endangered as a result.

To tell this ladybug from other ladybug species, look for the “M” (or “W”, depending on how you look at it) which seems to be printed in black on white just above its head. Photo: extension.umn.edu

When droves of Asian ladybugs enter the house, you can vacuum them up. Better yet, block all possible entrances to keep it outside.

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Rating: Beneficial in the garden; harmful indoors


Millipede

Millipede.
Millipede. Photo: curraheeshutter, depositphotos

The millipede has 2 pairs of legs per segment and up to 100 segments … but none really has the thousand legs their name promises: (mille = 1,000 + pede = feet). Its antennae are short. It moves slowly and curls up when disturbed. It’s a detritivore and soil aerator, mixing the different layers of soil together. And therefore, it’s useful to plants.

Strictly vegetarian, it doesn’t bite, but it sometimes releases a foul liquid when disturbed.


Rating: Beneficial


Praying mantis

Praying mantis.
Praying mantis. Photo: lightsource, depositphotos

The typical praying mantis is quite a large insect that comes in camouflage colors. It usually lands on a plant and hides there in plain sight, looking like a stem with leaves. It moves little if at all, and only very slowly, its front legs apparently bent in prayer. But if an insect passes by, a leg activates like lightning and grabs the intruder which will be immediately consumed … alive! A praying mantis will eat both harmful and beneficial insects, but the majority of its victims are harmful ones. You can buy praying mantises by mail to release in your gardens in order to control pests.


Rating: Beneficial.


Predatory mite

Predatory mite looking like a tiny red spider.
Predatory mite. Photo: Olei, Wikimedia Commons

This is a tiny yet still visible mite. It’s a solitary spiderlike arthropod with 8 legs, usually red in color. It ambles along at quite a speed for such a small creature. (Usually any bug that moves quickly is a predator; those that eat our plants tend to be in less of a rush!) You often find them wandering about on the soil and in mulch while you garden. Its nymphs parasitize several harmful insects, while the adult eats aphids in particular, as well as its own cousins, red spider mites (Tetranychus urticae).

(Despite their name, red spider mites are almost never red, but usually beige or greenish with two dark spots. If you see a red mite, it’s probably a beneficial one!)


Rating: Beneficial


Slug

Gray field slug on a yellow leaf.
Gray field slug, one of the most common garden slugs. Photo: Brian Eversham, Flickr

Slimy gastropod (mollusk) with eyes set on tentacles and no shell. Legless, a slug can glide over objects on its single foot. It’s a detritivore: a consumer of dead plant material, which the slug breaks down and makes available to plants. So, slugs would seem to be our friends!

However, most garden species are just as interested in living plants as dead ones if not more so and cause a lot of damage. The harm they do generally far outweighs any benefits.

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Rating: Mostly harmful.


Snail

Brown-lipped and white-lipped snails are highly variable. Photo: Angus Davison, Wikimedia Commons

Snails are much like slugs, but have a shell they can pull into so they can hide when disturbed.

There are thousands of species of snails, but only a few are harmful to garden plants, chewing holes into their leaves. Europe has more than its share of harmful varieties, whereas many North American snails are detritivores: they consume vegetable waste and clean gardens while enriching the soil, to the great benefit of plants.

The brown-lipped snail (Cepaea nemoralis) and its almost identical cousin the white-lipped snail (C. hortensia), with their bright yellow or brown-streaked yellow shell, are among the beneficial ones and are the most common garden snails (indeed, often the only garden snails) in many areas, such as Northeastern North America.

Many gardeners crush snails on sight, but before you do, check to make sure the species you’re dealing with is actually harmful!

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Rating: Beneficial or harmful, depending on local species.


Spider

Spider.
Spider. Photo: CreativeNature, depositphotos

Yet another 8-legged arthropod. Although they come in various sizes, up to that of a large fist, most garden spiders in temperate climates are small or relatively small. They’re all predators of harmful insects and gardeners should consider encouraging them rather than killing them. If one is in a location where you don’t want it, move it! A few are poisonous, especially in warmer climates, so do handle them with care.


Rating: Beneficial


Tick

Blacklegged tick
The blacklegged tick is not a problem for garden plants, but for those who take care of plants. Photo: KPixMining, depositphotos

There are many ticks, but these days we mostly hear about the blacklegged tick (deer tick) which transmits Lyme disease and other bacterial diseases to humans and their pets. Ticks are not insects, as they have 8 legs, but arachnids. This tick is not harmful to plants, but climbs onto plants, especially in gardens near wooded areas. It then uses the plant as a launching pad, raising itself high enough above ground so it can fix itself to a warm-blooded host. Other ticks have a similar modus operandi.

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Rating: Harmful.


True Bugs

Brown marmorated stink bug
Brown marmorated stink bug, introduced from Asia, is becoming a serious pest in gardens. Photo: Realitymages, depositphotos

There is a category of insects actually called “bugs.” To distinguish them from the generalized term bugs (meaning just about any creepy-crawly), it’s wiser to refer to them as “true bugs.”

True bugs tend to have flattened, rather shield-shaped bodies. And they are very much a mixed bag. Some, such as minute pirate bugs and flower bugs, are entirely beneficial, feeding on aphids, whiteflies and other unwanted pests. Yet others, notably stink bugs and shield bugs, consume or damage plants. And bedbugs are not too agreeable either!

Many, even the otherwise beneficial species, can give quite a painful jab with their proboscis if annoyed.

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Rating: Beneficial or harmful, depending on the species.


Wasp

Social wasp.
A social wasp can be distinguished from a bee by its “hourglass figure” (very narrow waist) and more streamlined appearance. Bees tend to be chubbier … and hairier. Photo: Ale-ks, depositphotos

So much variety! There are several hundred thousand species of wasps! Most wasps are tiny, black, and usually go unnoticed. They don’t sting humans and are vital predators (some) and pollinators (others).

There are also large wasps with a long ovipositor, such as the ichneumon wasp, which lay their eggs in the bodies of their victims. As a result, the baby wasps eat them alive, from the inside! And their prey are usually insect pests, like the caterpillars that eat our vegetable leaves and the borers that drill into the stems of our plants.

The most visible wasps, however, are social wasps, which are often striped black and yellow or white. They live in colonies with a queen and many workers. They carry out a certain amount of pollination, but are mostly predators that help gardens by protecting them from plant-eating insects.

True enough, social wasps are aggressive and their string is painful. You shouldn’t disturb their nest, but…

Rating: Beneficial except when a social wasp nest is located in a place where humans are bound to run into them. Don’t hesitate to consider such nests harmful and to eliminate them if that is the safest way to solve the problem.


Wireworm

Wireworm
Wireworm. Photo: Berislavskiy, depositphotos

This is an orange to brown elongated larva, segmented like an earthworm, but hard shelled. Also, it has six small legs near its tiny head while earthworms have none. The adult is the click beetle, an inconspicuous nocturnal beetle—usually black—that we rarely see.

Both eat the roots and bulbs of our plants and can destroy crops of potatoes, onions, etc.


Rating: harmful.


Now when you garden, I hope you keep your eyes—and mind!—more open. Many of the little bugs you encounter are actually friends of the garden and are worth helping. Who would have thought?

3 comments on “Bugs: Garden Friends or Foes?

  1. marianwhit

    I think I would rate our native mantids as beneficial and not the introduced Chinese ones…they are huge and will eat hummingbirds. It is good to learn the difference.

  2. Excellent information. Must admit as I get older and learn more am trying to learn more about the many insects seen in the garden. This seems to be the year for red ants and boy, are they aggressive. Have been bitten many times. Not feeling overly friendly towards them.

  3. The invasive snake worms, paper wasps invading my space, cabbage worms, tomato blight, chipmunks making trails through the yard, wild turkeys eating my berries, drought, heat, humidity – it’s been a year.

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