Combating, recognizing and preventing leatherjackets

Leatherjackets are the larvae of crane flies. The cabbage crane fly and the meadow crane fly are particularly common in the Netherlands and cause the most damage.

During the day, the larvae remain hidden in the soil, but at night they emerge to gnaw on the green parts of plants, usually as close to the ground as possible. The insect larvae do not eat the roots of plants, as many people think. This feeding damage can cause considerable damage to lawns, gardens and agricultural crops.

Leatherjackets are the larvae of crane flies and can grow up to 5 centimetres long. They can be recognised by their grey-brown colour and cylindrical, worm-like shape. Unlike many other insect larvae, such as grubs or wireworms, leatherjackets have no distinct front or back and lack legs. This makes them easy to distinguish from grubs, which have a curved body and distinct legs, and wireworms, which have a firm, hard texture and a more pronounced head structure.

The life cycle of leatherjackets begins when adult crane flies lay eggs in moist soil in late summer or early fall. After about two weeks, the eggs hatch and the larvae, the leatherjackets, emerge. These larvae feed primarily on green parts of plants from fall to spring. Towards the end of spring, the leatherjackets pupate in the soil. After a few weeks, the adult crane flies emerge, ready to start the life cycle over again.

Young leatherjackets that have just hatched do not cause any visible damage. They eat dead organic matter in the soil and do not come above ground. The older leatherjackets do cause damage.

Bald spots in the lawn
At the end of November, when the larvae reach their third stage, most damage to lawns becomes visible. This is because the grass does not grow quickly during this period, while the leatherjackets do eat the grass. The leatherjackets dig tunnels in the ground and emerge at night to eat plants above ground. They feed on weeds or grass stems and pull the plants along in their tunnels. A persistent myth is that leatherjackets eat the roots of the grass, but they do not.

Bald spots caused by birds
In addition to the feeding damage caused by leatherjackets, birds such as crows can also cause damage. Nothing will stop these animals from picking the tasty leatherjackets out of the ground, especially not when they come across a beautiful lawn. This often results in uprooted patches of grass where these birds have gone in search of leatherjackets.

Combating leatherjackets with nematodes is an effective and environmentally friendly way to get rid of these harmful larvae. Nematodes, also called nematodes, are microscopic worms that can penetrate leatherjackets and other insect larvae and transmit a bacterium. The bacterium eventually kills the leatherjackets. Here you can read how you can easily apply this biological control method.

Step 1: Choose the right nematodes
For the control of leatherjackets Felti or Carpo nematodes are most suitable, depending on the time of year you use them. Keep the nematodes in the refrigerator until you are going to use them.

Step 2: Prepare the nematodes
Mix the nematodes with water according to the instructions on the packaging. It is important to stir this mixture well so that the nematodes are evenly distributed. Use the mixture immediately after preparation to maintain its effectiveness. Preferably apply in the evening or on a cloudy day, the nematodes cannot tolerate UV light well. Make sure that the nematodes are applied with enough water so that they do not dry out.

Step 3: Application of nematodes
Apply the nematode and water mixture to the affected areas using a watering can or sprayer. Make sure the soil remains moist after application so that the nematodes can spread and do their work. If necessary, spray with a garden hose so that the nematodes can penetrate the soil properly.

Step 4: Repeat the treatment
For successful control, it is often necessary to repeat the treatment several times. This is especially important for heavy infestations. Usually, two to three treatments per season are sufficient to get the leatherjacket population under control. Read more on the page about when it is best to control leatherjackets with nematodes.

The best time to combat leatherjackets with nematodes is in the period from September to early November . At that time, the leatherjackets are still small and easier for the nematodes to parasitize. Not much damage is visible during this period. In the autumn, it is best to use the Felti nematode. The optimum soil temperature for the use of these nematodes is above 10°C.

In spring and summer it is possible to apply a repeat treatment of nematodes in the period March to June. For soil temperatures above 14 degrees the Carpo nematodes can best be used.

Prevention is better than cure! To prevent leatherjackets, you can take the following measures:

Keep your soil and lawn healthy
A strong and healthy lawn is less susceptible to leatherjackets. Regular fertilization, aeration and correct mowing will help. Ensure a well-drained soil, because leatherjackets thrive in damp conditions. Preferably water your lawn in the early morning rather than in the evening. This reduces the chance of a damp soil, which is attractive to leatherjackets.

Attracting natural enemies
Encourage the presence of natural enemies such as birds and hedgehogs in your garden. This can be done by hanging nest boxes and creating a varied garden.

Preventive use of nematodes
Do you suspect the presence of leatherjackets? Then release Carpo or Felti nematodes.

Check regularly
Regularly inspect your lawn to detect early signs of leatherjackets. This way you can intervene quickly before the damage becomes too great.

Catching leatherjackets
Leatherjackets can be caught by putting down a black plastic sheet or a garbage bag at night. The leatherjackets will think it is night and come up. In the morning you can easily catch them and remove them from under the black plastic.

Combating leatherjackets with garlic
One method to deal with leatherjackets is to use garlic extracts. The strong smell of garlic is said to repel leatherjackets, but this smell is also unpleasant to humans. Although some claim that garlic inhibits the growth of leatherjackets, no scientific evidence has been found for this. Furthermore, garlic does not actually ensure that leatherjackets are combated or disappear.

Chemical control of leatherjackets
Another option is to chemically combat leatherjackets. However, we strongly advise against this because chemical agents not only tackle leatherjackets, but also affect the entire soil life. These substances usually work on the nervous system of insects and do not distinguish between different species. This can cause serious damage to the soil ecosystem, which in turn affects the health of plants and lawns. That is why we always advise using ecological methods of pest control, in line with our mission and vision for a sustainable and healthy environment.