Wireworms: Small Pest, Major Annoyance!

They’re found in our gardens and lawns, but they are most annoying when they show up in our vegetable beds. We call them wireworms or click beetles. And if you want to control them, you need to get to know them better.

So, is this little pest a click beetle or a wireworm? Actually, it’s both!

The adult is very much a beetle. Small, elongated and black or brown, usually less than ¾ of an inch (2 cm) in length. And it has a surprising characteristic: when it’s on it back, it can launch itself into the air with a loud click. It then comes down right side up, landing on all 6 legs, ready to scurry away. Despite this unusual special effect, the average gardener rarely notices its presence of the dull-colored, nocturnal and very discreet adult. It’s rather its larva, called wireworm, that we run regularly into in our day-to-day gardening.

So, the wireworm, usually yellow, orange or brown, looks a lot like a small earthworm. It’s long, thin, segmented… altogether wormlike, but it has a head with tiny eyes (worms just have a mouth at one end). More visibly, though, there are three pairs of legs attached to the first segments whereas true earthworms simply don’t have legs. So, it’s an insect, not a worm. Also, its body is leathery and tough; not soft like a real worm. In other words, it crunches when you squish it instead of squooshing. (And don’t pretend you didn’t notice!)

Root and Bulb Eaters

Wireworms and click beetles are a formidable consumers of roots, tubers, bulbs and other underground plant parts. In the vegetable garden, it seems to have a particular affinity for potatoes, carrots, radishes, turnips, rutabagas and especially sweet potatoes. Also, any other part of the plant that touches the ground can be affected: leaves, stems or fruits. Any strawberries and tomatoes lying on the ground, for example, are likely to be damaged. Also, it mows down and eats young seedlings, often before they have even managed to push their way out of the soil.

However, since a lot of the damage happens out of sight underground, you don’t always notice the problem. Or again, only at harvest, when you dig up your root vegetables to find them full of holes and unuseable. Or when you uproot summer bulbs, such as dahlia and gladiolus, to bring them in for the winter… only to find them likewise looking like Swiss cheese. And rot, carried by the wireworm, often settles into the wounds, making for quite a mess.

We don’t always associate wireworms with the damage they cause. A plant can start to wilt, making you think it lacks water. But its real problem is that its roots are being chewed off and it can’t absorb water! We don’t always think to dig up a failing plant to see what had happened to its base. We often just add them to the list of “plants that I have lost without understanding why”… and that allows wireworms continue their ravages.

Distribution and Varieties

Wireworms are very common. In fact, they are found almost everywhere, in all terrestrial environments. They are only absent from Antarctica. There are nearly 10,000 species in over 100 genera (Limonius, CteniceraI, Melonotus, etc.). A typical home garden often houses several hundred wireworms belonging to a dozen different species! And entomologists identify species new to science every year!

Each of these species has its own favorite environment, but the preferred habitat of the most damaging wireworms is fields… and lawns. Lawns put up with large numbers of wireworms while not showing many symptoms. However, when the same species move into vegetable beds, more damage occurs. For that reason, spaces recently converted from lawn to vegetable or flower beds usually have the worst problems. So, owners of new gardens suffer the most and have to put extra effort into controlling the pests. As it can take two to six years for the larva to develop into an adult, depending on the species, the problem can be persistent.

In the vegetable garden, where the damage can be serious, simple crop rotation and interplanting can help confuse wireworms to some degree. Monocultures, on the other hand, encourage them. Also, allow birds like starlings and blackbirds to roam your gardens: they excel at seeking out wireworms. Or, if you raise chickens or ducks, know that they are excellent wireworm hunters too.

Life Cycle

Although there are many different species of wireworms, their life cycle is similar. Here’s a brief summary.

Wireworms overwinter in the soil as larvae or adults. Adults emerge in late spring when soil temperatures warm and lay their eggs in moist soil. The larvae then hatch and feed on the roots and other underground parts of plants for 1 to 6 years, depending on the species, getting larger over time. Mature larvae form a pupa in a pupal cell up to 8 inches (20 cm) deep under the ground, then after 3-4 weeks turn into an adult beetle, which remains in the cell until the following spring.

And then it all starts again.

Because generations overlap, wireworms of all sizes and ages of each species can be present in the soil at the same time.

Controlling Wireworms

Quite honestly, wireworms are not easy to eliminate. Often, the best that can be done is to reduce their population to acceptable levels. However, here are some avenues to explore in your effort to keep them under control.

Destroy Them as You Garden

Probably the technique most used by gardeners in controlling wireworms is simply to crush them when they encounter them. During planting, dividing, harvesting or weeding, for example. It’s simple but effective!

Personally, I drop them into a bowl and put it on the patio so the birds can come and eat their fill. Sometimes there are bird lineups waiting for a wireworm to carry home to a nest.

Garden Above the Ground

Female click beetles prefer lawns and lawnlike environments for egg-laying. They have no particular interest in container gardens. So, you’re not likely to find wireworms in a balcony, terrace or rooftop garden unless you bring in contaminated soil.  

Even the “instant vegetable garden” of the fiber pot type (read An Instant Vegetable Bed You Can Put… Anywhere!), one placed directly on a lawn, has a bottom that is an impenetrable barrier for this insect. Vegetable gardens produced according to the so-called laidback gardener method (A Vegetable Bed from Scratch … the Laidback Way), i.e. by placing a layer of fresh soil over a barrier of newspaper, are also protected from wireworms present in the original soil. They’re unable to migrate up through the fiber to reach the new plantings.

Distance Can Also Be a Barrier

Wireworms very often move into gardens from nearby lawns. They end up serving as a sort of wireworm nursery, producing an endless supply of them. Leaving a 1 ½ to 2 foot (45-60 cm) strip of heavily mulched weed-free soil all around the garden bed also provides an anti-worm zone which can help deter them.

Predators And Diseases to The Rescue

In lawns, where wireworms are abundant, but rarely do significant damage, the same beneficial nematodes (Steinernema spp., Heterorhabditis spp., etc.) that destroy white grubs and Japanese beetle larvae will also control wireworms. You just have to apply them to gardens according to the instructions given on their packaging. These days, nematodes are readily available in garden centers in many areas.

On the other hand, BTG (Bacillus thuringiensis galleriae), a bacterial disease also used against white grubs, has no effect on wireworms.

There are also wireworm diseases, including certain strains of the fungus Metarhizium brunneum. They can help control wireworms when applied to the soil. Some are available to farmers (particularly to European potato growers), but I’ve seen nothing yet for home gardeners.

The same goes for click beetle pheromones, which can be used to upset their reproduction. They give off compounds like those of female click beetles, making it possible to attract, trap and dispose of the males. Farmers have access to such products (if they know where to look), but not home gardeners.

Wireworm Potato Trap

Here is a very effective little trick for trapping wireworms.  And it uses only products you already have at home! Just make a wireworm trap using spuds from the kitchen.

Wireworms are highly mobile and move laterally through gardens, seeking out interesting scents. They can cover up to 12 feet (3.6 m) in a single night if there is a strong enough smell.

Cut a raw potato* into pieces of at least 1 x 2 inches (3 cm x 5 cm) in size and insert a skewer into each one. This is so you can find them readily later.

*You could also use a piece of carrot or sweet potato.

Now bury the pieces in the garden about 2 to 6 inches (5 to 15 cm) deep and about 3 feet (1 m) apart, leaving the skewer visible above the ground.

Special Tip: It can also be helpful to add a few rolled oats (yes, the breakfast cereal!) to the bottom of the trap hole. They make the tuber even more inviting for wireworms!

After 24 to 48 hours, dig up the potato chunk using the skewer as a guide. This is best done at night when wireworms are most active. Remove the wormy potato segment with its wireworms and replace it with a fresh piece. Repeat as long as you keep finding wireworms (they’re active from mid-spring through fall).

You’ll be surprised by the large number of wireworms you can catch this way!

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So, little by little, take control of the wireworm population in your yard… so you can garden in peace!