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

The European crane fly (Tipula paludosa), or ‘Daddy-longlegs’, is a familiar visitor to homes and gardens throughout late summer and early autumn. Their larvae, known as leatherjackets on account of their tough, leathery skin, can cause real problems for both cereal farmers and lawn enthusiasts. Read on to learn how to identity and manage crane flies and their larvae in your garden.

There are over three hundred species of crane fly (Tipula spp.) in the UK, and they are all entirely harmless to humans and animals. Their appearance in your garden does not necessarily spell trouble for your lawn and killing the crane flies in the grass will not 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 the larvae of only two species that can cause damage to lawns and of these Tipula paludosa 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 can sometimes be 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 two weeks. They mate, and 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. The crane fly eggs hatch in the grass after two to three weeks and the young larvae then 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 there can survive frosts up to 5cm below the surface. In the spring they emerge and feed voraciously on grass roots, and 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. There are several 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 appear 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 cranefly 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 and can be removed and fed to garden birds.

How to get rid of crane flies

Once you have correctly identified the crane fly larvae and understood their life cycle, you can set about controlling them and preventing future attacks. It is unlikely that any single method alone will completely eradicate a major infestation. By combining several measures and performing them regularly you are more likely to see an improvement.

Nematodes: get rid of crane flies naturally

The entomopathogenic nematodes Steinernema carpocapsae are naturally occurring, microscopic soil organisms which are mixed with water and applied to the 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, 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

It is prohibited for both home gardeners and farmers to use insecticides against 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

Fertilizers 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 things you can do to combat crane fly larvae without the use of either insecticides or fertilizers.

Home remedies

As well as the use of nematodes, there are several more control measures that can reduce the crane fly larvae population. Covering affected areas with black plastic and collecting larvae that burrow to the surface overnight, as suggested above, can help to reduce numbers if performed regularly. Do not leave black plastic on the lawn in daylight hours as it 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. Small lawns can also be covered with a light horticultural fleece to prevent adults from laying eggs in the first place. Research by the Soil Association using a 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, but 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. Eight cloves in five litres of water will provide a good starting point.

Your options in a nutshell

• Adult daddy-longs are harmless and do not damage humans or lawns.
• The larvae, or leatherjackets, can damage lawns when found in large numbers but can be controlled naturally.
• The use of insecticides is prohibited, and calcium cyanamide fertilizers are not recommended.
• Nematodes are a safe and effective option when applied correctly.
• Increasing the mowing frequency when adults emerge will decrease the egg burden.
• Covering small lawns with fleece can prevent the laying of 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 applying the control measures above alongside a few other simple prevention techniques. Leatherjackets are unlikely to damage a healthy lawn with strong, deep roots, so repairing or overseeding your lawn after an infestation is a good first step. Attracting birds to your garden 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. Other general maintenance tasks such as aerating, scarifying and fertilising the lawn can also help to keep it in good heart. However, 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.