If you’ve ever encountered those strange, squishy, little brown grubs in your lawn, you may be wondering what they are, and what harm they could possibly cause.
Harmless as they may look, these peculiar pests can cause damage to lawns, seedlings and small plants by eating the roots.
If you discover yellowing patches of grass in your lawn, it’s possible that leatherjackets (crane fly larvae) are the culprits. Fortunately, there are many ways to deal with these wriggly pests. From encouraging predatory birds to spraying garlic solution and applying parasitic nematodes, all will reduce, or eliminate them from your garden.
In this article, we’ll take a detailed look at leatherjacket bugs and how you can successfully remove the larvae from your lawn.
What are leatherjackets?
Leatherjackets are the larvae of crane flies, also known as daddy longlegs. These large, clumsy flying insects, that love to fly right into you, may seem pointless, but the flies and their larvae are an important food source for many birds including starlings, rooks and golden plovers.
There are over 300 species of crane fly (Tipulidae) in the UK. Completely harmless, crane flies are part of the family of true flies including mosquitos.
Most of the crane fly life is spent in the larval stage. The larvae of most crane fly species don’t feed on living roots, but for those that do, the damage can be extensive, particularly for lawns. The most common types of crane flies are the European and marsh crane flies, both are considered agricultural pests in some parts of the world due to the damage that they can inflict on grass and cereal crops.
What do leatherjackets look like?
Small, brown and wriggly, I’m sure many a sci-fi movie monster has been inspired by these otherworldly creatures. Leatherjackets are about 3cm long and dull brown in colour.
Looking a bit like a legless caterpillar, leatherjackets are often confused with chafer grubs which are larger with shiny white bodies and black heads. Unlike many ground-dwelling larvae, leatherjackets don’t have an especially noticeable head and their uniform colour can make them tricky to spot in the ground.
Also known as leatherjacket worms, you’ll find these critters residing just below the soil surface and if you’re doing any lawn edging or planting, you’re particularly likely to encounter them. You might also find leatherjackets under plant pots and in areas of shallow gravel.
The crane fly life cycle begins with the emergence of the adult fly in August/September. This can vary a little from region to region.
The adult stage of the crane fly is a romantic but short one. Living for just 10-15 days, their sole purpose is to mate and lay eggs. They don’t have mouths so are unable to eat during this stage. Female crane flies will hatch out with a supply of mature eggs and will find a mate soon after emerging.
Daddy longlegs eggs are usually laid in the grass (around 300 at a time) and the larvae hatch out after a few weeks. Their growth is measured in ‘instars’ and they will take around 8 months to grow and pupate. The leatherjacket larvae will dig more deeply into the soil as the temperatures drop, rising up again in spring. Crane flies spend the vast majority of their life in the leatherjacket stage.
The crane fly larvae will pupate around the month of June, emerging as adult crane flies from August onwards, ready for the new cycle to begin.
Are leatherjackets good for the garden?
Although the larvae of some crane fly species are completely harmless, those that live under our lawns have voracious appetites and feast on the roots of the grass.
Although soil-dwelling leatherjacket larvae have some benefits, they help to promote a healthy soil ecosystem, more than a few of these grubs can cause damage to your grass.
Leatherjackets damage lawns by eating the roots of the grass. If you’ve seen how quickly caterpillars can lace the leaves of your vegetables, leatherjackets and grass roots are no different.
A small, balanced number of leatherjackets won’t cause a problem but if they are eating the roots more quickly than the grass can recover, sections of the lawn will begin to die. A healthy lawn can sustain around 40 leatherjackets per square foot, any more than this and you will start to see the signs of infestation.
Larger birds and animals that feed on leatherjackets can also cause damage to the grass, particularly during the summer when the grass is drier.
What causes leatherjackets in the garden?
Crane flies tend to lay their eggs in areas of grass. There will often be more crane flies after a wet autumn because the larvae and pupae prefer damp conditions.
Crane flies are attracted to the light from our houses and short grass provides the perfect spot for egg-laying. A leatherjacket infestation is often just down to bad luck, people may have one infestation and no more problems, or could experience repeat infestations. The number of adult crane flies will vary and where they deposit their eggs is quite random, some even lay eggs whilst flying.
What are the signs of leatherjackets in my lawn?
Discoloured patches of yellow-brown, weak grass in your garden are often a sign of leatherjackets insects in the lawn. If you have a leatherjacket infestation, you may be able to easily pull up large sections of turf where the roots have been damaged. Damage to lawns will be at its worst in spring, when the larvae are at their largest and if winter has been damp and mild, it may be particularly bad.
If you dig into the soil, you’ll likely find a few of the brown larvae, particularly around border and path edges.
How to get rid of leatherjackets in your lawn
If you’re unlucky enough to have a leather jacket infestation in your lawn, there are several ways that you can tackle the problem.
Because of environmental legislation withdrawing all insecticide and pesticide treatments in 2015, no chemical treatments for leatherjackets are available. This is great news for the environment and there are many other effective ways to remove these pests from your garden.
1. Ensure the grass is strong
Healthy grass means healthy roots and, unless you have an extensive infestation, a few daddy longlegs larvae won’t do any noticeable damage to your lawn.
Keep your lawn healthy by regularly mowing it, once a week should be adequate during the summer months. Keep your grass well aerated and well fed, and it’ll produce long, strong roots that will be able to withstand most leatherjacket feeding frenzies.
2. Attract leatherjacket feasting birds
Leatherjackets are a juicy delicacy for birds so attracting them to your garden is a good move. Crows, starlings, rooks, magpies and golden plovers are particularly partial to a leatherjacket or 5.
You can attract birds to your garden by providing suitable food and water. Starlings will enjoy mealworms and suet balls.
3. Set a trap
Another good tip is to encourage leatherjackets to come to the surface of the soil. You can do this by wetting an area of the lawn and placing a black plastic sheet or large bin bag over it. Anchor it to the ground using heavy stones or tent pegs and leave it overnight or for a day or two. Any leatherjackets should rise to the surface of the lawn and will provide a feast for the birds. Simply repeat with another section of your lawn until you’ve covered the whole area.
4. Apply nematodes
Leatherjackets can be successfully controlled using insect pathogens like fungi and bacteria, specifically Bacillus thuringiensis. These bacteria and fungi are introduced into the soil by nematodes, pathogenic, worm-like, multi-cellular insects with smooth bodies.
Nematodes that will specifically target and kill leatherjackets can be purchased online, or from garden centres. They work by releasing a fungus or bacteria into the larvae which then destroys them.
When to apply nematodes for leatherjackets
To apply nematodes, you’ll first need to cut your grass short. Mix the treatment with water and apply it to the lawn with a watering can. Although nematodes sound a little scary, they are a completely natural treatment and harmless to humans, pets, wildlife (except leatherjackets) and the lawn.
The best time to apply nematodes is when the larvae are at their most active. So from mid-April to mid-May or from September to October. Be sure to read the instructions on the packet as the dosage may be different depending on the time of year that you apply the nematodes.
5. Spritz on the garlic
If you prefer to try a DIY leatherjacket repellant, garlic is proving to be an exceptionally effective treatment.
Incredibly simple to make, crush several garlic cloves into a bowl, add boiling water and leave overnight, then strain it to remove the larger pieces which may clog up your sprayer. Mix with water then liberally apply the solution to the grass.
The bitter taste of the garlic will prevent the larvae from feasting on the grass and they’ll wriggle away to find sweeter-tasting grass elsewhere.
6. Get digging
For a completely free treatment, you can simply dig down and remove the larvae yourself. This won’t be suitable for a large area of grass, but if you’ve got a small lawn, you can effectively remove leatherjackets from any affected areas using a small trowel.
You shouldn’t need to dig too deep to uncover the larvae because they tend to live around 3 inches below the soil. It may take a few goes to remove the larvae but if leatherjackets are causing noticeable damage to your lawn, it’ll be time well spent.
You can pop the leatherjackets you’ve removed onto a bird table or tray, they won’t be around for long!
How to repair leatherjacket lawn damage
Fortunately, extensive lawn damage due to leatherjackets isn’t common, but what do you do if they have savaged your lawn?
Once you’ve treated the soil for leatherjackets (see above), you’ll need to remove any yellowing or dead grass from the lawn. This is easy enough to do, just take a sharp knife or edging tool to cut around the damaged section and carefully lift it out.
Once you’ve removed all the damaged patches, apply good-quality topsoil to the bare soil, making sure it’s level with the rest of the lawn and re-seed. Choose grass seed that’s suitable for the soil and aspect of the garden.
Take care to keep the patches well-watered as the new grass establishes. You can read more about lawn reseeding here.
How do I control leatherjackets in my lawn?
Although there’s nothing you can do about crane flies laying their eggs in your garden. There are steps that you can take to control leatherjackets in grass. The most effective method is an application of specific leatherjacket-targeting nematodes which can be done twice a year.
Unless you dig up your lawn, it’s almost impossible to know whether you have a leatherjacket issue until it’s too late. Using nematodes will kill any larvae that are in the lawn, preventing any damage. Also, take care to keep your lawn healthy, it’ll help to ensure that any damage caused by leatherjackets is minimal.
Now you know what those strange little brown grubs are, you can rest assured that they’re very unlikely to cause much damage to your garden. If you do notice sections of your lawn are yellowing, dig down and see if leatherjackets are the cause of the problem, you’ll easily find plenty if it’s the case.
Arm yourself with black plastic, a garlic spray, befriend the birds or introduce nematodes to your garden and your lawn will quickly bounce back to life.
If you’ve had success with any of the methods we’ve listed, please let us know in the comments below.