Wireworms & click beetles
Wireworms are the larvae of click beetles. They are slender, hard and shiny, yellowish to chestnut brown and up to about 1 1/2 inches long, with three pairs of short legs near the head. They spend two to six years or more in the soil, eating seeds before and after they germinate, boring into the stems of seedlings and tunnelling into potatoes, carrots and other roots. Damage is worst in ground that was recently lawn, pasture, hay or grassy weeds. The adults, the click beetles, do no harm to the plants. No parasite or biological product has been reliable against wireworms in the field. In a garden, trap them with buried bait before planting and avoid planting potatoes straight into turned-over grass.
Wireworm larva and tuber tunnel; click beetle adult inset. Photo: pending.
Identification
The larvae look like mealworms: long, thin, cylindrical and hard-bodied, shiny, and yellowish to chestnut brown, with six short legs clustered near the head. Grown larvae are 3/8 to 1 1/2 inches long, depending on the species. A few species are soft and whitish, with yellow-brown heads and tails.
The adults are click beetles, slender, streamlined beetles, usually brown and 1/4 to 1/2 inch long for the common crop species, with the body tapering towards the rear. A flexible joint between the thorax and abdomen lets them flip into the air with an audible click when they are placed on their backs, which is how they got their name. Viewed from above, two backward-pointing spines on the segment behind the head wrap around the front of the wing covers. Click beetles do not damage plants.
Easily confused with
- MillipedesHarmlessAlso called "wire worms" for their cylindrical shape, but they have two pairs of legs on most body segments and crawl on the surface. A wireworm has only six legs, all near the head.
Damage symptoms
Wireworms feed on whatever is below ground. Early in the season they bore into seeds before or during germination, so rows come up patchy or not at all, and they tunnel into the underground stems of seedlings, which wilt and die. Later they bore into potato tubers, carrots and sweet potatoes, leaving narrow round holes. In potato the holes run straight or at an angle up to about 1/2 inch deep, without going right through. Damage is often worst in cool, wet springs, and it tends to come in patches.
- Gaps in rows where seed never came up, especially beans, peas and corn
- Seedlings that wilt and die, with a small hole in the stem below the soil
- Narrow, round tunnels in potato tubers, up to about 1/2 in deep
- Holes and scars in carrots, sweet potatoes and other roots
- Patchy damage, worst in ground recently taken out of grass or pasture
Lifecycle & degree days
Click beetles emerge from the soil in spring and summer, fly at night, and lay eggs in the soil, usually in grassy or weedy ground and sod. The larvae then spend years in the soil: two to six years in Kentucky's account, and two to eleven years across species in Utah State's. They move up and down the soil profile with temperature and moisture, and they are drawn to the carbon dioxide given off by germinating seeds. Because generations overlap, a field or bed holds wireworms of every age at once. A wireworm problem in spring usually means there was grass, sod or a grassy cover crop on that ground within the last three to five years.
- Larval life
- 2–6 years typically (2–11 across species)
- Eggs
- 200–400 per female, late spring–summer
- Egg hatch
- 3–7 weeks
- Pupa
- About a month, in the soil
- Overwinters
- Larvae, and new adults in their pupal cells
Host crops
Wireworms prefer cereals and grasses, but damage many crops. Potatoes and other starchy roots suffer the most visible harm, because tunnelled tubers cannot be sold. Corn and large-seeded crops such as beans and peas lose stand when the seed is eaten. UMass also lists cabbage, lettuce, pepper and sweet potato. UC IPM notes that carrots are especially attractive, which is what makes them useful as bait.
Monitoring & action thresholds
Kentucky and Utah State both use an average of one or more wireworms per bait station, set before planting, as the point where preventive treatment is worth considering. That is a farm figure. We found no home-garden number, but the bait stations work the same way in a bed and show whether wireworms are present before you plant potatoes.
Bait before planting. Kentucky's method: bury half a cup of untreated corn and wheat seed in a hole about 4 inches deep and 9 inches wide, three weeks before planting, and dig it up after two weeks. Utah State uses a soaked stocking of oats, wheat, corn or barley 6–8 inches deep, covered with dark plastic, for 7–10 days. UC IPM notes that baiting works only once the soil is about 50 °F (10 °C) at 4–6 inches. Count the wireworms in the bait and the soil around it.
Biological control
No biological control is reliable against wireworms. Utah State Extension says that no effective parasites or biological insecticides are known, and that entomopathogenic nematodes are ineffective. Laboratory and shade-house trials support that: in a 2024 test of 16 nematode populations, wireworms were highly resistant, with 3–43% killed after 56 days, and in a Montana shade-house trial Steinernema feltiae did no better than untreated soil. The insect-killing fungus Metarhizium brunneum infects wireworms and has cut damage in some European trials, but results in the field are inconsistent and the US products are not labelled for wireworms (see Metarhizium). UMass names two biological products: PFR-97 (Isaria fumosorosea), labelled for soil use on outdoor crops, and Majestene (heat-killed Burkholderia), which has a 2(ee) label for wireworms in potato and sweet potato. Neither has a page here. Birds eat some wireworms but do not keep numbers down.
Cultural controls
Wireworms are a legacy of grass. Most garden control is about timing, trapping and not giving potatoes to a freshly dug lawn.
- Do not plant potatoes, carrots or corn straight into ground that was lawn, pasture or grassy weeds in the last three to five years (UMass)
- Trap them with carrots: plant a nearly full-grown carrot every 2 1/2–3 ft, pull them every 2–3 days, remove the wireworms and replant (UC IPM)
- Or bury baits of germinating peas, beans or corn 2–4 in deep under a board, 3–10 ft apart, and collect the wireworms after a week (Utah State)
- Lift potatoes promptly once the vines die, and clear dead plants and tubers, which can be reinfested
- Avoid thick grassy cover crops such as winter rye or sorghum-sudangrass in the three years before a susceptible crop (UMass)
- Drying the top soil in midsummer, or repeated cultivation in late spring and early summer, reduces some species
Chemical, last resort
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
University of Kentucky ENTFACT-120, Wireworms (Bessin, rev. 2026)
Utah State University Extension, Wireworm fact sheet (Davis, Karren & Roe)
UC IPM, Wireworms (Home and Landscape)
UC IPM Pest Management Guidelines: Potato — Wireworms (Haviland & Trumble, 2019)
UMass Extension Vegetable Program, Wireworms
Sandhi, Shapiro-Ilan & Reddy, J. Econ. Entomol. 113:2104 (2020)
Chacon-Hurtado et al., J. Invertebr. Pathol. 207:108231 (2024)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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