Getting Rid of Leatherjackets

I’ve seen first-hand the damage leatherjackets can do to lawns; not only do they turn the grass brown but I’ve seen them completely kill it off too.

But what are leatherjackets? Where do they come from, and what’s their lifecycle? How they can be killed or deterred?

Welcome to my guide to getting rid of lawn leatherjackets – all of the methods and advice on this page are based on my experience of dealing with this destructive pest.

What Are Leatherjackets?

Leatherjackets are the larvae of well-known insect called a crane fly, you’ve almost certainly seen these clumsy insects in or around your home, and you’ve probably heard them being called Daddy longlegs.

I see them often in late summer or autumn in my garden and you probably have too.

Daddy longlegs are part of the Tipulidae family of insects and can be found worldwide.

The leatherjacket is the grub or larvae formed from mating daddy longlegs.

Leatherjacket Lifecycle

Daddy longlegs are active from late summer into autumn when males and females will mate.

After mating the female will lay eggs, typically under grassy areas of the garden.

Within a couple of weeks, grubs, known as leatherjackets, will hatch and burrow deeper into the undergrowth.

Initially devouring roots and even coming up to the surface to eat grass blades, the leatherjackets will then burrow deeper into the ground during the winter to avoid the frosts and cold weather.

Leatherjackets aren’t very active during the winter so even if you can’t see them, I don’t think you should assume they aren’t there.

In spring, when the ground temperatures rise, they will reappear and start consuming the grass roots and some top growth.

Once the leatherjacket has consumed enough nutrients and grown to a suitable size, it will pupate – this is the final stage of the lifecycle prior to the grub transforming into a daddy-longlegs.

The lifecycle then repeats itself and this is how they spread.

Here is a brief timeline:

• August to September – eggs are laid in the soil.
• September to October – eggs hatch and leatherjackets are born.
• October to December – leatherjackets devour roots and some top growth.
• December to March – the leatherjackets are less active and burrow deep to avoid the cold.
• Late March to early June – leatherjacket activity increases and it’s at this time that I’ve seen the damage to lawns.
• June to August – the grub changes to a pupa.
• August to September – the daddy-longlegs emerge and mate.
• August to September – daddy-longlegs leave eggs in the lawn, and the lifecycle starts all over again.

Image from Nemasys Leatherjacket Control.

How to Tell if Your Lawn is Infested With Leatherjackets

I worked in the landscaping industry for years, so I know several grubs can damage lawns, and one should not automatically assume that it’s leatherjackets.

Fortunately, I know of a simple test that anyone can use to detect them.

Here’s how I’ve detected leatherjackets in the past, this only works from late March to June:

First, I would find an area of the lawn that looks damaged, an unusual bare or brown patch, for example. Next, I would do a classic pull test; healthy grass will have strong roots and won’t be easy to pull up. I’ve found that diseased or damaged grass will have weak roots that give way easily.

Assuming the grass pulled up easily, I would then dig up a section of the lawn and undersoil and check which type of pest is causing the damage.

Try my method and here’s how you tell the difference between the grubs you may find:

• Chafer grubs are white with a black head and from what I’ve seen, they usually curl up – read how to get rid of white lawn grubs here.
• Wireworms are very thin, up to 2.5cm and are orangish in colour.
• Cutworms are caterpillars and are large and blue-grey in colour.
• Leatherjackets are dark-coloured, cylindrical, straight and over 2cm long (see photos below).

How Much Damage Can Leatherjackets Do To a Lawn?

A handful of leatherjackets is unlikely to do too much damage, but from my experience, I know that they can spread quickly and, if not dealt with, can become an infestation within a few years. 

All of this happens under the grass without you noticing it until the damage is done.

I’ve seen large infestations devastate lawns and tell-tell signs are usually:

• Patches of yellow and brown grass.
• The grass feels spongy underfoot.
• Thin or bare patches.
• Excessive damage from large birds and animals who dig for the grubs.

Leatherjackets will consume the roots and during nighttime, I’ve seen them come to the surface to consume the grass blades as well.

I’ve even seen badgers and foxes tear up the grass as they search for the grubs.

Also, I have seen the leatherjacket grubs be more active during a milder, wetter winter, so you may find that the damage could be light one year and extensive the next.

How to Get Rid of Lawn Leatherjackets

As their name suggests, leatherjackets are tough little pests, and I’m not aware of any chemical treatment that’s effective.

I’ve had success in the past by using these methods:

Option 1) Nematodes 

Nematodes are microscopic worms that kill common garden pests, including chafer grubs, slugs and leatherjackets. I have used these many times and can confirm that they do work.

There are many different types of nematodes, but the variant sold by Nemasys attacks and kills off leatherjackets without harming your grass, plants, other insects, pets or children.

I have seen or heard of nematodes causing damage or having an adverse effect on a garden.

Nematodes are alive and must be kept in a fridge, so I only ever purchased them at the correct time of year and deployed them as soon as they arrived. 

Each pack of Nemasys contains up to 50million nematodes. I’ve found them very easy to use – I just added them to a watering can and sprinkled them on the lawn. To prevent them from drying out, which would kill them, I would then water the lawn daily for a couple of weeks.

The best time to apply the nematodes is between late August and the end of October when the grubs are young and weak. For effective treatment of large infestations, I’ve had to apply them two or three times for two years, as I’ve found that some usually persist.

While it is possible to apply the nematodes in the spring, the leatherjackets will be hardened and less likely to succumb to the treatment. If you’ve ever picked up one of these pests, you’ll know how tough their skin is.

If you do want to try a spring application, I suggest doubling the normal dose and only applying it when the temperature is above 12°C.

Option 2) Prevention 

I have found a way to prevent leatherjacket infestations but based on my experience, it works best with some of the other methods on this page.

In late summer and early autumn, I would notice lots of daddy longlegs in my garden and I would try to stop them from mating by:

• Mowing more frequently as soon as I saw the daddy longlegs.
• Raking the lawn when I saw the daddy longlegs.
• Collecting grass cuttings and disposing of them off-site.
• Not watering the lawn during August and September.

Fortunately, daddy longlegs don’t live for very long as their only aim is to mate, so I would only need to take these steps for a few weeks at most.

Option 3) The Tarp Method 

This is an excellent method that I’ve used dozens of times.

The goal of this method is to encourage the leatherjackets to the surface, where I would then pick them up myself by hand or by raking them into a bucket.

First, I would pick a time of year when the leatherjackets grubs are active and near the surface (see image above) I would then water the lawn and give it a good soaking.

I would then lay a dark tarpaulin or dark plastic cover over an infected section of the lawn. If it was windy, I would peg it down.

I’ve found it best to leave the grass covered overnight and possibly for a day too. The tarp will create a warm, moist, dark environment that will encourage the leatherjackets to the surface, this is something we in the trade call “sweating them out”.

I would then get up at sunrise and lift the tarp, where I would see them on the surface.

I would pick them up and move the tarp to another part of the garden and repeat the process.

The tarp method won’t lift all of the leatherjackets to the surface but is a cheap way to control their numbers, so they don’t spread like crazy and I’ve had very good results, sometimes lifting dozens of them at each attempt.

Option 4) Encourage Natural Predators 

Every garden pest will have natural predators, and the leatherjacket is one of the tastiest meals a large bird can find.

By encouraging more birds into my garden, I’ve reduced leatherjacket numbers to an acceptable level.

I’ve found this method works particularly well with option 3 (the tarp method), as the birds will eat the grubs while they’re on the surface of the lawn.

There are many ways to encourage birds into the garden:

• Buy squirrel-proof bird feeders.
• Bird feeding stations.
• Just leaving seeds out in the garden early every morning.
• Place water bowls and birdbaths in the garden.

It can take a while for birds to get used to the regular feeding, but once they do, they should come back every day to feed and should pick off some of the leatherjacket grubs.

The only issue I’ve had with this method is that sometimes the birds peck and dig up the lawn as they search for the grubs.

Summary

Leatherjackets are a destructive garden pest that can wreak havoc to lawns by devouring roots and top growth; they also attract large predators such as badgers and foxes which I’ve seen damage the lawn further by digging.

Leatherjacket numbers can fluctuate from year to year depending on how many eggs survive the autumn and the weather conditions in winter and I’ve witnessed leatherjacket numbers explode after a wet and mild winter period. I don’t think you should assume the infestation is under control just because you’ve seen a reduction in the number of grubs one year, I suggest completing the treatment methods until you’re sure they’re gone, which could take a few years.

While there aren’t any chemical solutions available (that don’t nuke everything in the garden), you can use nematodes and also introduce natural predators to your garden. 

For a quick fix, I suggest the tarp method on one section of your lawn at a time while periodically picking up the surfaced leatherjackets.

Other steps that I’ve found can help are; reduce your watering regimen during the autumn, mow the lawn frequently, dethatch and collect grass cuttings.

I’ve had better results by acting quickly and taking preventative measures rather than waiting until an infestation is severe.

Do take note of the leatherjacket lifecycle as they aren’t always active, and nematode predators, for example, are more likely to work during the autumn.

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