Garden Insects Identification: Name Pests by Damage

To identify a garden insect, match the damage on the plant to the kind of feeding that caused it, then find the insect itself on the undersides of leaves, on stems or at the soil line. Holes and missing leaf edges come from insects that chew; sticky, curled, speckled or streaked leaves come from insects that suck sap. Once you know which kind you are looking for, the list of suspects is short.

If you find the insect, photograph it and InsectLens identifies it. The group pages linked below let you confirm the result.

Each line below pairs a symptom with the pests that cause it, from the Gardener's Supply Company plant pest photo gallery unless another source is named.

• Small round holes in leaves: flea beetles, on many vegetables and fruits.
• Leaves eaten down to the veins: Japanese beetle adults, on roses, beans and fruit trees such as apple, cherry and plum.
• Large amounts of leaf and fruit gone on tomatoes: tomato hornworm.
• Irregular holes and ragged edges on leaves and flowers: earwigs. See earwigs.
• Seedlings cut off at the soil line: cutworms.
• Winding tunnels inside leaves: leafminers, on spinach, lilac, apple and ornamentals.
• Sticky leaves that turn black: aphids, whose honeydew often grows a black sooty mould (UC IPM), or whiteflies, which also cause yellowing. Many ants on a plant often point to aphids, because ants feed on the honeydew and protect the aphids from their enemies (UC IPM).
• Curled, distorted leaves: some aphids inject a toxin that makes leaves curl (UC IPM); tarnished plant bugs cause distorted growth and puncture wounds.
• Fine pale speckling, bronzed leaves, fine webbing: spider mites. UC IPM says the first damage is a stippling of light dots, and dense webbing appears when numbers are high.
• Silvery streaks and distorted growth: thrips.
• Squash plants wilting: squash vine borer larvae boring into stems, or squash bugs sucking sap, which causes wilting and yellowing.
• Roots or root crops damaged: root maggots on cabbage and onion, wireworms in root crops, tubers and sown corn seed.
• Plants chewed to the ground: grasshoppers.

Gardener's Supply lists 35 common pests in eight groups. The ones gardeners meet most often:

• Caterpillars: tomato hornworm, cabbageworm, cabbage looper, corn earworm, codling moth (in apples and pears). See caterpillars.
• Beetles: Colorado potato beetle, cucumber beetle, Japanese beetle, Mexican bean beetle, flea beetle, asparagus beetle. See beetles.
• Small sap feeders: aphids, whiteflies, mealybugs, scale, spider mites, thrips. See aphids.
• True bugs: squash bug, tarnished plant bug, stink bugs. See true bugs.
• Soil pests: cutworms, wireworms, root maggots. White C-shaped larvae in lawns and beds are covered on grubs.

The UK and European list from the Big Bug Hunt adds slugs and snails, sawflies, vine weevil and allium, chrysanthemum and horse chestnut leaf miners, and several root flies (cabbage, carrot and onion).

Many insects in a garden eat the pests. UC IPM names lady beetles (adults and larvae), lacewing larvae, syrphid fly larvae and parasitic wasps as the main natural enemies of aphids; parasitic wasps leave behind swollen, crusty "mummified" aphids. Gardener's Supply lists ladybugs, parasitic wasps and green lacewings as beneficial, found on plants with aphids, whiteflies, mealybugs, scale or caterpillars. The Big Bug Hunt adds ground beetles, hoverflies, spiders, centipedes, dragonflies and wasps to its beneficial list.

So a lady beetle larva, which looks nothing like the adult, is a reason not to spray. Compare with lacewings and see beneficial vs pest insects.

• Check often. UC IPM advises looking at plants at least twice a week while they are growing fast, so an infestation is caught early.
• Turn leaves over. Spider mites live in colonies mostly on the undersides of leaves; a single colony can hold hundreds (UC IPM).
• Shake over white paper. Adult spider mites are under 1/20 inch long and look like moving dots; shaking foliage over white paper shows them (UC IPM).
• Look for two tubes on the rear end. Aphids are 1/16 to 1/8 inch, pear-shaped, and have a pair of tube-like cornicles pointing backward; UC IPM says this feature separates aphids from all other insects.
• Try water first on sturdy plants. UC IPM says a strong stream of water or shaking the plant knocks aphids off.
• Know the season. Spider mites peak from June to September in hot, dusty conditions and on water-stressed plants (UC IPM).

Yes, you can upload a picture of a bug to find out what it is. Photograph the insect itself, not only the damage: get it in sharp focus from above and, if you can, from the side, and include the plant it was on. Small insects such as aphids, thrips and mites need a close-up or a hand lens photo. Photograph it and InsectLens identifies it, then compare the result with the damage list above. If the photo only shows damage, the list on this page narrows the suspects before you search for the insect.

Research and drafting for this page used AI assistance. Every figure, date and quotation was then checked line by line against the sources listed at the bottom of the page, each of which was opened while writing. Pest control products are not recommended here; follow your local extension office for treatment choices, and read and follow the label of any product you use.

Indoor plants get a shorter list of pests than a garden, and each leaves a recognisable sign:

• Scale: oval bumps about 3 to 4 mm long with a waxy covering, brown to yellow, on stems and leaf undersides (Homestead Brooklyn). They are easy to mistake for part of the plant.
• Mealybugs: wingless, oval, segmented and covered in white wax, with cottony egg masses, sticky honeydew and black sooty mould. They hide in the crown, in branch crotches and on stems near the soil (UC IPM).
• Aphids: soft-bodied, in clusters, leaving sticky honeydew (Homestead Brooklyn); the two tubes at the rear identify them (UC IPM).
• Whiteflies: look like tiny white moths and fly up when the plant is disturbed; leaves yellow (Homestead Brooklyn).
• Spider mites: nearly invisible; fine webbing, pale stippling and bronzing on leaves (UC IPM). See mite identification.
• Fungus gnats: dark, delicate, mosquito-like flies 1/16 to 1/8 inch long around damp potting mix; the larvae have a shiny black head and a whitish, legless body (UC IPM).
• Thrips: silvery patches on leaves and tiny black specks of droppings (Homestead Brooklyn).

Two pests come up most. Mealybugs, because UC IPM says their waxy coating repels most contact insecticides and their habit of clustering in hidden spots makes them hard to reach; its advice includes dabbing them with a cotton swab dipped in a solution of 70% or less isopropyl (rubbing) alcohol in water and discarding heavily infested plants. Spider mites, which Homestead Brooklyn calls probably the most feared houseplant pest because they are so difficult to get rid of; UC IPM notes that they prefer hot, dusty conditions and water-stressed plants, and that sprays of water, insecticidal oils or insecticidal soaps can be used.

• White paper test for spider mites: shake a few leaves over a sheet of white paper; disturbed spider mites run around quickly and are easy to see. A 10X hand lens shows them clearly (UC IPM).
• Potato slice for fungus gnat larvae: push raw potato chunks, cut side down, into the potting mix; larvae gather underneath (UC IPM).
• Yellow sticky cards: catch adult fungus gnats (UC IPM) and whiteflies (Homestead Brooklyn), which tells you what is flying and how many.