Crane Flies


Crane flies are often described as looking like a very large mosquito; however their mouthparts do not enable them to take a blood meal. They are large insects that  range from 1-2.5 inches long and have long, thin legs that can be about two times the length of the body. Their wings are about three inches long and are folded over their body when the insect is at rest. While crane flies may appear menacing, they actually are harmless to people.


While crane flies are not harmful, they do become a nuisance when large numbers of adults swarm. They are attracted to both indoor and outdoor lights. Crane flies spend most of their time as larvae or pupae living underwater in streams, the edges of ponds, within wet logs, or in other damp places. These flies emerge as adults for a quick mating spree before dying. They are beneficial as decomposers of organic matter in streams. However, there are some crane flies that damage turfgrass, a problem that is especially damaging to grass located in areas that receive low amounts of sun, resulting in reduced plant vigor.


Adults feed on flower nectar and the larvae consume decaying plants, leaves, fungi or plant roots. Some crane fly species are predators on living aquatic insects, while other crane fly species do not eat at all as adults.


Some species of crane flies live in aquatic sources, others in a terrestrial or decaying vegetation source. They frequently occur in moist woodlands, streams and land located in flood planes. Still other species are found in piles of decomposing leaves, compost piles and moist areas of lawns that receive small amounts of sun.


Crane flies go through complete metamorphosis – egg, larva, pupa and adult. As eggs hatch in their preferred habitat, full-grown larvae leave their water source and crawl onto mud or water logged soil and burrow in it. Here the larvae develop into pupae where they overwinter and become adults in the warm spring months. The adult female usually contains mature eggs upon her emergence from the pupal stage and will immediately mate if a suitable male is nearby. Adults only live a few days.


Evidence of crane flies may include damage to grasses in which they develop, but for the most part their presence goes unnoticed until large mating swarms are seen.


The most important and practical way to help prevent crane flies is to make sure that doors and windows are not left open when crane flies swarm. Also, making sure that unnecessary lights are turned off after dark will help to reduce the potential of crane flies becoming a nuisance around the home or other buildings.


Generally, there is no need to use control procedures or products since in their natural habitats, crane flies are considered a beneficial aquatic insect and the adults that may be a nuisance only live for very short time period. However, for crane flies that may damage turf by feeding on grass roots, using approved insecticides may be warranted.