Leatherjackets, larvae of crane flies

What are leatherjackets?

You may have come across them before: the greyish-brown to black larvae (leatherjackets) you can find in the soil of the lawn in the garden or on the sports field. However, you may have only seen large bare patches in the lawn and not yet encountered the larvae. Whatever the case, chances are that the damage to the grass was caused by the larvae of the crane fly, which we call 'emelts'. The crane fly lays its eggs in the ground around August and September and does so in numbers of 300 to 400 eggs at a time. In doing so, it prefers long grass, which the crane fly larva likes to eat. It takes about 2 weeks for the crane flies' eggs to hatch and when they do, they think of only one thing: hunger!

The cow longlegs mosquito and meadow longlegs mosquito

The leatherjackets feed on small plants, blades of grass and their roots, and thus if more than 10 leatherjackets per square metre are present, they can create a devastating pest. There are several species of crane flies: hence 'emelt' is a generic term. However, the most common crane flies in the Netherlands are the cow crane fly and the meadow crane fly. The cow moose produces two generations per year: it usually lays its eggs in spring and early summer, between April and June to be precise. You will see a second generation pupate in late summer and early autumn: between August and September. The meadow long-legged midge, which only hatches around August and September, therefore produces larvae that you will see causing damage mainly in late autumn until May.

The damage done by leatherjackets

As just mentioned, it is grass, which is on the menu of the larva of the crane fly. This therefore explains the damage caused by the leatherjackets and why most people prefer not to see crane flies in the garden: large bare patches mark the areas where the leatherjackets feast. They hide during the day, but emerge at night to eat the greenery, young parts of the plant as well as the roots of the grass, which can completely destroy the root collar of a young plant (often grass). You will see this happen most often in a lawn, on a sports field or golf course, but you may also encounter the leatherjackets in young seedlings or plants. Apart from voracious damage to roots and blades, the leatherjackets also invite birds, moles and mice to come and dig over the grass in search of the larvae, which can wreak havoc on the grass' roots in the process. Leatherjackets may cause serious damage, but their adult counterparts, the crane flies, do not. They only eat nectar and stay away from lawns.

So you can recognise leatherjackets by their grey-brown, almost black body that, when you touch it, feels somewhat leathery. The body of leatherjackets grows between 2 to 5 centimetres long and has no legs. Leatherjackets look a lot like worms and move in a similar way. As with worms, it is difficult to determine the front and back of an emelt. Their length depends on the stage of life: the larger they are, the older, and closer to the time of pupation to long-legged mosquito.

Controlling leatherjackets with nematodes

Controlling leatherjackets can fortunately be relatively simple and also done in an environmentally friendly way. One of the natural control methods available is the use of nematodes. The use of nematodes (also known as nematodes) against leatherjackets is successful in most cases and a popular approach, because the nematodes do not pose a threat to soil life in the lawn or turf, but they are a natural enemy of the leatherjackets. So, as an organic gardener, you can use nematodes to control blackhead without fear of damaging the soil. 

Nematodes against leatherjackets

The nematodes used to control leatherjackets are also known as 'nematodes'. The Latin name of nematodes is 'Steinernema Carpocapsae'. Nematodes are used to control various insects, including the offspring of crane flies. Nematodes are parasitic nematodes: minuscule and invisible to the eye. Because they are so small, they are able to invade the leatherjackets, after which they will spread their bacteria into the crane fly larva. These bacteria multiply and infect the emelts, after which they will die. This usually happens around the third to fifth day after application of the nematodes and continues for about six weeks. When all the emelts have died, the nematodes will also leave: in fact, if they no longer have prey, they will leave the soil.

Nematodes like moist soil

To do their job, the nematodes must be able to move quickly and easily. To do so, the soil must be moist and airy. Fortunately, this is the case in the Netherlands and Belgium regarding most soils. Is your soil not? Then you can prepare the soil for the nematodes by perforating it to a depth of 10 centimetres. You do this with a special tool called a 'mestrike'. In addition, make sure the soil is well moist by putting a sprinkler on the lawn for at least an hour. Your soil should now be ready for nematode application.

You can buy nematodes quickly and easily online these days: in addition, you can often find them in shops for gardeners. The package contains a bag of nematodes and instructions for use. Fortunately, it is not difficult to apply the nematodes. To do this, fill a watering can with lukewarm water, to which you add the nematodes. Make sure you mix the water and nematodes well before emptying the watering can over the lawn areas infected with leatherjackets. You use about 0.5 million nematodes per square metre, but don't worry about overdosing: this is not possible. Applying too few nematodes, on the other hand, is! So for an effective approach, make sure you always use 0.5 million nematodes per square metre. In most cases, a package contains 25 to 125 million nematodes. So make sure you work with enough nematodes and order an extra package if necessary.

To ensure yourself an effective approach, it is advisable to keep the soil well moist for six weeks after applying the nematodes. Spraying the lawn daily for half an hour is enough to keep the nematodes active.

When to control leatherjackets?

The best time to control leatherjackets is when they have just hatched from their eggs. This is because this is when the crane fly larvae are at their weakest, which makes it easier to put an end to the black-backed embankment pest. As mentioned earlier, the crane fly usually lays its eggs at the end of summer: that is, around late July, early August. It takes about 2 weeks for the eggs to hatch. That makes this period - to be precise, from August to November - the perfect time to release the nematodes. Another way to determine when you should control leatherjackets is to pay close attention to whether you see long-legged mosquitoes flying around the garden. If this is the case, deploy the nematodes two weeks after seeing the first crane flies. However, keep in mind that the soil temperature must be at least 14°C, otherwise the nematodes will die before they have even completed their task.

Because leatherjackets, like many other species of larvae, can remain present in the soil for a long time, it sometimes takes several years for a population of leatherjackets to disappear completely. You may therefore find that you will have to apply the treatment for controlling leatherjackets several times to be completely rid of an infestation. However, do not worry too quickly: if the treatment is applied adequately and consistently, the infestation of leatherjackets should be able to be controlled relatively easily and effectively and, eventually, not have to return.