What Are Crane Flies and Are They Harmful?

Crane flies (Family Tipulidae) look like giant mosquitoes, being up to 3cm (1-1/4″) in length, with a long slender abdomen, very long thin legs, narrow wings, and long antennas with multiple segments per stalk. They can be brown, green or white in colour.

They’re sometimes called ‘Daddy long-legs’, a name more commonly used to refer to the Daddy long-legs spider, or Cellar spider, Pholcus phalangioides.

Adult crane flies are harmless insects, they are weak fliers, and they don’t bite, sting, or suck blood. In fact, their mouthparts don’t allow them to feed at all, but only drink water, so they don’t live very long. Even though crane fly larvae can live for up to a year, the adults only live for a few days or weeks.

Crane flies belong to the taxonomical order Diptera, which is derived from the Greek words “di” (two) and “ptera” (wings), a reference to the characteristic that true flies only have a single pair of wings, and that the second pair of ancestral hind wings are reduced to club-shaped modified wing structures known as halteres, which vibrate at high speeds during flight to function as flight stabilizers, much like a gyroscope in a plane.

Other species of the Diptera order such as houseflies, hover flies and mosquitos also have halteres, but crane fly halteres are among the easiest to view with the unaided eye.

Mosquitoes look different, they’re much smaller and have a distinct long, pointed proboscis which they use to puncture the skin to feed. Only female mosquitos feed on blood, they do so to source protein so they can become fertile and lay eggs. Male mosquitos are nectar feeders and can be distinguished by their very feathery antennae.

Where Do Crane Flies Live?

Crane flies live in moist environments such as forests, woodlands, floodplains, streams and urban areas, because their larvae (grubs) need moisture to survive.

Most species of crane fly larvae live in damp soil, or beneath layers of decomposing leaves in wet locations where they can get sufficient moisture. They can also be found in compost piles under piles of decaying organic matter. Some crane fly larvae are aquatic, and live in fresh water.

What Do Crane Fly Larvae Eat?

Crane fly larvae have chewing mouth parts and primarily feed on decaying plant matter. They are beneficial insects as they act as decomposers, helping break down plant matter to return the nutrients to the soil.

There are a few exceptions though, some crane fly species can be found much drier environments, such as agricultural fields, dry rangeland and even in desert environments. A small number of these species are considered pests of farms and lawns as they feed on roots of seedling field crops, forage crops, and turf grasses.

The crane fly larvae are known as leatherjackets due to their tough leathery skin. These grubs are greyish-brown in colour, up to 40mm (1-3/4″) in length, and do not have any legs or a discernible head. They live beneath the soil and eat lawn and seedling roots.

There are no effective chemical controls available for leatherjackets.

Thankfully, there’s an effective biological control, the parasitic nematode Steinernema feltiae, a microscopic worm-like organism (sold as ‘Nemasys’) which can be watered onto soil, only needs to be applied once, and is environmentally safe. These nematodes enter into the larvae and infect them with certain bacteria which is fatal to them.

Remember though, the majority of crane fly larvae are harmless, they just help break down organic matter!

References

• Galveston County Master Gardeners – Beneficials in the Garden, Crane Flies <https://aggie-horticulture.tamu.edu/galveston/beneficials/beneficial-29_crane_flies.htm&gt;
• Australian Museum – Crane flies https://australian.museum/learn/animals/insects/crane-flies/
• Croprotect – Latherjackets https://croprotect.com/pests/leatherjackets