Crane flies: life cycle, larvae & how to get rid of daddy long legs

The European crane fly is a familiar visitor to homes and gardens and can cause problems for farmers and lawn enthusiasts. Read on to learn how to get rid of daddy long legs and their larvae.

There are over 300 species of crane fly (Tipula spp.) in the UK, all of which are entirely harmless to humans and animals. Their appearance in your garden does not always spell trouble for your lawn and getting rid of the crane flies themselves will not necessarily help to protect it. In fact, they serve as an excellent food source for bats and birds and their presence frequently indicates a healthy ecosystem. It is their larvae — commonly known as ‘leatherjackets’ on account of their tough and leathery skin — that can cause damage to lawns. The larvae of only a few species will cause this damage. Of these, the European crane fly is the most common visitor to UK gardens. The other, the marsh crane fly (Tipula oleracea), is almost identical and only on close inspection do subtle differences in its eyes, antennae and wingspan become apparent.

Daddy long legs: life cycle and problems with crane fly larvae

The adult crane flies have long legs and grey-brown bodies of up to 2.5cm in length. Their veined wings are transparent and span up to 5cm. In flight and on foot they are slow and ungainly. The larvae are tubular and vary in colour from black to grey-brown, reaching a maximum length of 4cm in the spring. They are sometimes confused with other lawn grubs, but are easily identifiable thanks to their apparent lack of legs and a head. The pupae of the crane fly are red-brown and clearly divided into segments.

Crane fly life cycle

Adult crane flies emerge from their pupae in the soil from August until October and live for only a fortnight. After mating, the females deposit up to 300 eggs on the lawn. The adults are weak fliers, managing only a few metres at a time, and are frequently found close to larvae habitats. Once the crane fly eggs hatch in the grass after 2 to 3 weeks, the young larvae begin to feed on the roots and shoots of nearby plants. As temperatures drop and winter approaches, the larvae burrow further into the soil and can survive frosts up to 5cm below the surface. In the spring, they emerge and feed voraciously on grass roots — this is when the leatherjackets inflict the greatest damage. They retreat once again to pupate below the soil surface in summer, and finally emerge as adult crane flies to begin the cycle again.

Damage caused by crane flies

Small numbers of larvae in your lawn are not a problem and are tolerable without the need for treatment. The damage caused by a serious infestation will be most apparent in spring, particularly after mild, damp winters. Here are some of the symptoms to look out for:

• Yellow-brown and wilted patches in the lawn
• Visibly eaten blades of grass
• Slowed growth
• Small holes in the lawn caused by larvae burrowing to the surface
• More birds appearing on the lawn, particularly starlings, magpies, crows, and rooks
• Affected grass will come up easily when pulled due to root destruction
• Secondary damage by birds and animals disturbing the lawn to reach larvae

You can conduct a simple test to confirm the presence of crane fly larvae. Soak an affected area of lawn with water and cover it securely with anything that is impenetrable to light, such as a black plastic bin bag. Uncover it the next morning and if larvae are present, they will be sitting on the surface of the lawn. You can simply remove the larvae and feed them to garden birds.

How to get rid of crane flies

Once you have confirmed the presence of this lawn pest, you can set about controlling the crane fly larvae and preventing future attacks. It is unlikely that any one method alone will completely get rid of crane flies. You are more likely to control crane flies and their larvae effectively by combining several measures and carrying them out regularly.

Nematodes: get rid of crane flies naturally

The entomopathogenic nematodes Steinernema carpocapsae are naturally occurring, microscopic soil organisms that you mix with water and apply to your lawn. They ambush the young crane fly larvae and infect them with symbiotic bacteria. The bacteria alter the larvae to make them edible for the nematodes which feast and reproduce inside them. Unsurprisingly, this quickly kills the larvae, and the cycle continues until few victims remain. This fascinating process is harmless to humans and animals and can be highly effective by applying the treatment between mid-September and mid-October. This is when the newly hatched larvae are at their most vulnerable (but also harder to spot). For best results, the nematodes must not dry out, so an application to moist but well-drained soil on an overcast day is best. Treating the edges of an affected patch is also important to prevent the larvae from spreading out to new areas.

Insecticides against crane flies

The law prohibits both home gardeners and farmers from using insecticides to get rid of crane fly larvae. They are potentially toxic to humans and pets and are harmful to many beneficial insects.

Using calcium cyanamide to kill crane fly larvae in the lawn

Fertilisers containing calcium cyanamide are sometimes used to control crane fly larvae. However, a report in 2016 by the EU Scientific Committee on Health and Environmental Risks identified calcium cyanamide as potentially harmful to humans and the environment. Fortunately, there are other ways of controlling crane flies and their larvae without the use of either insecticides or fertilisers.

Home remedies

As well as the use of nematodes, there are several more control measures that can help to get rid of crane flies in your garden. Covering affected areas with black plastic and collecting larvae that burrow to the surface overnight, as suggested above, can help to reduce numbers if done regularly. Do not leave black plastic on the lawn in daylight hours as the grass will quickly turn yellow. When you notice the first adult flies of the season, begin mowing your lawn more frequently and collect all the clippings. This will significantly reduce the number of eggs in the lawn. If you have a small lawn, you can cover it with a light horticultural fleece to prevent adults from laying eggs in the first place. Research by the Soil Association using garlic solution against larvae has also shown promising results when applied to affected areas in autumn. Garlic sprays are available from garden centres and online. However, you can also make your own by steeping crushed garlic cloves in boiling water overnight and applying the strained solution to affected areas. The strength of the spray will depend on the quantity of garlic used. We recommend starting with eight cloves in 5 litres of water and going from there.

Crane flies and your options in a nutshell

• Adult daddy-long legs are harmless and do not damage humans or lawns.
• The larvae, known as leatherjackets, can damage lawns when found in large numbers but can be controlled naturally.
• The use of insecticides is prohibited, and calcium cyanamide fertilisers are not recommended.
• Nematodes are a safe and effective option for controlling crane fly larvae when applied correctly.
• Increasing the mowing frequency when adults emerge will get rid of crane fly eggs in the lawn.
• Covering small lawns with fleece can prevent the crane flies from laying eggs.
• Covering affected areas with black plastic brings larvae to the surface for collection.
• A homemade garlic solution spray discourages the larvae.

Can you prevent a crane fly infestation?

Crane flies produce just one generation each year, and there will be no larvae left in the lawn once all the adults have flown. It is possible to prevent future infestations by carrying out the control measures above alongside a few other simple prevention techniques. Leatherjackets are unlikely to damage a healthy lawn with strong, deep roots. Carry out a lawn repair after infestation, or overseed your lawn to discourage future attacks. A high-quality seed mixture, such as our Plantura Lawn Overseeding Mix, is ideal for restoring bare or patchy lawns and is best applied in spring or autumn. Attracting birds to your garden at any time of year will provide you with an enthusiastic team of crane fly predators and a preventative autumn application of nematodes will boost the resilience of the soil.

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Other general maintenance tasks such as aerating, scarifying and fertilising can also help to keep your lawn in good health, which in turn helps to control crane flies. That said, over-feeding a lawn or doing it at the wrong time could cause damage. Discover the dos and don’ts of lawn fertilisation in our separate article on how and when to feed your lawn.