What are those large mosquito-like insects that find their way into my home? Although they look similar to mosquitoes, they are much larger but do not bite. What are they and where do they come from?
These are expected questions that Galveston County Master Gardeners get during spring and early summer. These mosquito-like flies are called crane flies. Crane flies look like Texas-sized mosquitoes and have been incorrectly called mosquito hawks. (The term "mosquito hawk" generally refers to dragonflies.)
Crane flies belong to an order of known as Diptera. The term Diptera is derived from the Greek words "di" meaning two and "ptera" meaning wings, and refers to the fact that true flies have only a single pair of wings.
Crane flies in the Galveston-Houston region are fragile with long legs and are tan in color. The body of a crane fly adult measures about ˝ inch in length. The body has a narrow abdomen and almost absurdly long legs—our measurements revealed several legs exceeding 1˝ inches.
Each wing is about ˝ inch in length. Located behind each wing is a modified wing structure known as a haltere (plural: halteres). The haltere resembles a golf club and is visible to the naked eye at close examination. Halteres vibrate at high speeds during flight. They function as flight stabilizers, similar to gyroscopes on airplanes that prevent excessive roll, pitch or yaw. Halteres occur on many other species of Diptera including houseflies (a widespread pest) and hover flies (an important beneficial in our gardens). However, crane fly halteres are among the most easily viewed without the aid of a hand lens.
Several species of crane fly occur in Texas. Crane fly larvae have a grey-brown colored and cylindrical shaped body which may bear fleshy lobes on its posterior, i.e., its rear end. Occasionally, the segments toward the posterior end of the body can be greatly expanded.
The larvae commonly occur in moist environments such as woodlands, streams and flood plains. They are found under layers of decomposing leaves in wet locations in December and January. In compost piles, they can be found below the pile of decaying vegetation.
Larvae of some crane fly species can be found in open fields, dry rangeland and even in desert environments. Some species have also been reported to feed on roots of forage crops, turf grasses and seedling field crops. The larval stages of crane fly species occurring in Texas have not been reported to feed on vegetable transplants or garden plants.
The larval stage has chewing mouth parts and feed primarily on decomposing organic matter. Crane fly adults only live for a couple of days and do not usually feed.
Spiders notwithstanding, crane flies rank high on the list of uninvited critters which cause the most bedlam in a home. Attracted by the light inside the house, they fly in the open window or door and start to flap against lampshades or walls. However, they are medically harmless as they do not sting, suck, or transmit disease pathogens.
Beginning mid-February and lasting into April, large numbers of adult flies emerge and rest on plants and walls outside the home where they are attracted to lights. Unfortunately, they sometimes gain entrance into homes through doors or other openings.
An important step in managing crane flies is preventing adults from entering the home. This can be accomplished by ensuring that window and door screens are in place and in good repair. So-called "bug lights" (incandescent bulbs with a yellow color) can be installed as most flying insects, including crane flies, do not have a strong attraction to “bug lights.” Otherwise, merely leave outside lights off during evening hours. These practices will not completely eliminate these flies from being in or around the home, but they will reduce their numbers in these areas.
The main thing to remember is that the adult stage of crane flies is harmless. In fact, their biology is such that their contribution to our ecosystem is largely beneficial because the larvae feed on decaying-organic matter and thus assist in the biological decomposition process.
Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.
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