Of the 9,000 wireworm species around the world, some are serious agricultural pests that can also affect home gardens. Like with many other pests, it’s the immature stage of the insect and not the adult that inflicts damage. Wireworms are the long, wire-like larvae of the click beetle, which got its name from the audible click it makes when, after being turned on its back, it swiftly flips back into the right position.
If you detect wireworm damage in your garden, you’ve already had wireworms in the soil for several years. Wireworms have a particularly extended lifecycle from two to three up to six years, a good part of which the larvae spend feeding on plant stems and boring into stems, roots, and tubers. Getting rid of wireworms as soon as you detect them is key to prevent damage not only this season but also in future gardening years.
Wireworms primarily feed on grasses, corn, grains, and potatoes, but they also go after many other vegetables.
What Do Wireworms Look Like?
Being familiar with the life cycle of wire worms is just as important for their identification as their appearance. You not only need to know what to look but also when to look for it.
There are many different species of wireworms that attack crops; however, they share a similar lifecycle—a complete metamorphosis from eggs to larvae to pupae to adults.
The Life Cycle of Wireworms
Wireworms spend the most part of their life cycle as larvae in the soil. They stay in the same location during their entire life cycle. As adults, they return to where they hatched, which often results in multiple overlapping generations of wireworms in different sizes and ages in the same location.
In the spring, when the soil has warmed up to 50 to 55 degrees Fahrenheit, the adult beetles emerge from their overwintering location in the soil. They mate and over the summer, the females lay eggs on the soil surface, in soil cracks, or near roots. They lay a single egg at a time but on an ongoing basis and up to 300 eggs total. Preferred places for depositing the eggs are grassy or weedy locations or fields. During their entire life span of nine to 12 months, the adults stay mostly near the soil surface. When their egg laying is complete, the adults die.
Depending on the temperature, the eggs hatch after a few days to a few weeks.
The larvae feed on seeds and underground parts of plants for the remainder of the summer, then overwinter and restart their feeding the next spring. This pattern continues for two to three years until the larvae create an underground cell to pupate in the late summer. The new adult beetles emerge from the pupa within a few weeks and remain in the soil until the next spring.
How to Identify Larvae and Adults
The newly hatched larvae are white with dark brown jaws and about 1/16 inch long. The grown larvae measures 1/2 to 1 1/2 inches in length and 1/8 inches in width. After the first month, some species develop a hard body shell, while others are soft. The color of the larvae ranges from shiny yellow-brown or chestnut brown to tan-brown. The body is slender, cylindrical, and jointed, with three pairs of short legs behind the head. The larvae of the different species are usually identified by the pattern on the last segment of their abdomen.
The pupae are about 1/2 inches long, white, soft, and very fragile. They resemble the adult beetles in shape and size.
Above ground, you’ll only spot the adults: beetles with a hard-shelled, narrow, slender body, and 1/3 to 1/2 inches long, that is tapered towards the rear end. The color ranges from brownish or reddish-brown to grayish, tan, or black. What gives away the species is the clicking sound when the beetle is turned on its back and flips itself over again.
The eggs are tiny, pearly white, and round and difficult to detect in the soil, even more so because they are not laid in clusters but individually.
How to Get Rid of Wireworms
Your best line of defense against wireworms is monitoring and prevention, especially if you had an infestation in the past. Once wireworm larvae are feeding on your plants, they cannot be efficiently combatted with insecticides.
Bait Them and Remove Them By Hand
The most efficient mechanical method to remove wireworms is to bait and kill them. However, this only works if the population is still small. Dig trenches two to four inches deep, at least three feet apart. Fill the trenches with a germinating peas, beans, or corn and cover them with a board. The wireworms will be attracting by the food source and gather in the trench. Remove the board after about one week and crush the wireworms.
Signs of Wireworms
The preferred host plants of wireworms in home gardens are grasses. Bold, wild, and cultivated grasses, both sweet corn and ornamental corn, and potatoes. They also feed on a wide range of other vegetables, including beans, beets, cabbage, carrots, cucumbers, lettuce, muskmelon, watermelon onion, leeks, parsnips peas, radishes, sweet potatoes, and flowers.
If you suspect you have wireworms, keep an eye out for wireworms when tilling or digging up your garden soil. The larvae are typically found in the upper six inches of the soil. When the soil is too hot or too cold, however, they can burrow down further. How deep they are in the soil also depends on soil moisture. Wireworms like it moist and cool, which can make it tricky to find them in dry soil during the summer.
Inspect the soil around ungerminated seeds, as well as the upper four to six inches of soil around damaged plants. Check their roots and lower stems to see if larvae are present.
Poor germination rates of your vegetable crops can be a sign of wireworms eating the insides of seeds, feeding on the seeds right before, or just after germination.
The larvae also feed on young seedlings, chewing small holes in the cotyledons, and in the stems. As a result, the seedlings die because they are stunted or girdled.
Older plants aren’t spared. The larvae feed on the smaller plant roots, hair roots, and as well as underground parts of stems, depriving the transport of nutrients and water. As this attack is ongoing throughout the entire season, the plants have no chance to recover; they become stunted or withered and eventually die.
The larvae also burrow winding tunnels and channels into larger roots and taproots. Edible roots and tubers become deformed by forming a secondary root (“forking”). The scarring and channels on the root surface or the inside make them inedible.
What Causes Wireworms?
While wireworms can be found anywhere, areas with that were previously farm fields, pastures, grassland, fallow fields, or sod are especially prone to wireworm infestations. They are filled with host plants where click beetles lay their eggs. Often new housing developments are built in this type of location. Because of the long life cycle of wireworms, it is possible that you see an infestation in your yard three to five years after the land was developed.
Another location that attracts wireworms are poorly drained areas with moist, heavy soils. If, in addition to the soil being wet, sod has been plowed under in this type of location, it becomes an even more suitable breeding ground for wireworms.
As beneficial as cover crops such as rye and adding organic matter are for amending soil, they can also attract wireworms, especially if the drainage is poor.
How to Prevent Wireworms
Unlike other insects, due to their extensive life cycle, wireworm infestations don’t develop within a few days or weeks in a single season. This gives you a bigger time window to prevent and control their populations with preventative measures.
Wireworms prefer wet soil. Improve areas with poor drainage to deter them from settling in your garden.
Make sure to follow crop rotation in your garden beds. Because wireworm larvae overwinter in the soil, newly seeded crops or transplants are an easy target for the pest. If you’ve had a major problem with wireworms, you might want to go one step further and abstain entirely from growing any susceptible crops the next year—even in a different area of your garden.
Adjusting the planting time of vegetable crops that germinate faster in warmer weather can help avoid wireworm damage. The longer seeds sit in the soil before germinating and the longer plants take to get established, the longer they are vulnerable to wireworm attacks. If you wait a little longer until the soil has warmed up more, you give the seeds a better chance of survival.
Using soil insecticides as little as possible encourages natural predators of wireworms, such as ground beetles.
Another form of biological control is to introduce Steinernema carpocapsae to your garden soil before planting. These beneficial nematodes have shown promising results in treating areas with large wireworm populations. Steinernema carpocapsae is available in products for home gardens.
In case of a major infestation, or when you want to plant crops that need to be planted early in the season, apply an insecticide to fend off wireworms. Make a note that these insecticides must be applied to the soil before planting.
Insecticides against wireworms include products with bifenthrin, pyrethrins, and zeta-cypermethrin as active ingredients. They are available for home garden use in granule or liquid form.
How do you kill wireworms?
Baiting them with germinated seeds then removing them mechanically is the best way to kill them. Insecticides are not effective against the larvae.
What do wireworms turn into?
The larvae become click beetles.
How do you get rid of wireworms in a vegetable garden?
Monitoring and prevention are crucial to get wireworms under control. In case of a major infestation, you can introduce nematodes to the soil or apply an insecticide, but these measures must be taken before planting.
“Wireworms.” Wisconsin Horticulture.
Wireworms. Utah State University.
Wireworm. University of Massachusetts Amherst, Center for Agriculture, Food, and the Environment.
Teresa Rusinek. Wireworm Biocontrol Update. Cornell University Blogs.