Because they are perceived to eat mosquitoes, making them a beneficial insect.
It also is neither a mosquito nor a hawk, but it does catch mosquitoes in the air; it hawks them all right. In some places a mosquito hawk is a damselfly. Damselflies are very closely related to dragonflies, and like dragonflies, damselflies are neither hawks nor mosquitoes, but do hawk mosquitoes. Most people who call dragonflies mosquito hawks also call damselflies mosquito hawks. Both are in the order Odonata, and again, an entomologist in any country should know the name Odonata, and what it means. Crane flies are in the order Diptera and therefore are practically unrelated to dragonflies and damselflies.  There are many myths concerning mosquito hawks. This is interesting when you discover that there are two insects that are commonly called this name. Both dragonflies and crane flies are commonly known as mosquito hawks, and yet both have very different interactions with mosquitoes. Also commonly refered to as mosquito hawks, crane flies resemble very large mosquitoes. Although it is rumoured that mosquito hawks eat mosquitoes, that is not the case with crane flies. Crane flies do not bite people either, but prefer to feed on the roots of a variety of grasses. Mosquito hawks as pest control. Best Answer: There isn't any insect with the common name of 'mosquito hawk.' The name is used with a variety of large insects, including dragon flies. Dragon flies have two sets of parallel wings that stick out perpendicularly from the body, and they cannot be folded in. Some people to dragon flies as a mosquito hawk. Another insect that looks like a gigantic mosquito is the crane fly.  Mosquito hawk-dragon fly. Dragon flies are commonly refered to as mosquito hawks. This may be due to the species habit of killing mosquitoes. An adult dragonfly can eat hundreds of mosquitoes a day, as well as consuming a variety of flies and other insects. Also commonly refered to as mosquito hawks, crane flies resemble very large mosquitoes. Although it is rumoured that mosquito hawks eat mosquitoes, that is not the case with crane flies. Crane flies do not bite people either, but prefer to feed on the roots of a variety of grasses. Mosquito hawks as pest control. Also called darning needle, devil's darning needle, ear sewer, mosquito hawk, skeeter hawk, snake doctor, snake feeder, spindle. Regional Note: Regional terms for the dragonfly are numerous, providing good evidence for dialect boundaries in the United States. plural dragonflies. Any of various large insects of the order Odonata or suborder Anisoptera, having a long slender body and two pairs of narrow, net-veined wings that are usually held outstretched while the insect is at rest. Some people call them “mosquito hawks” because they eat mosquitoes. They also eat gnats, flies and other flying insects. Dragonflies have even been seen eating winged termites as they fly out of the ground. In some cultures, dragonflies are considered good luck. In other cultures, they are considered bad luck.  Crane Flies (Tipulidae) are delicate insects varying in size from ¼ inch to as large as 1½ inches in length. The largest crane flies are sometimes called daddy-long-legs, gully nippers, or mosquito hawks. However, they do not bite people and they do not eat mosquitoes. Some species of crane flies emerge from aquatic sources and others from terrestrial or decaying vegetation sources. Crane flies are not predacious and usually many times larger than a typical mosquito. Adults are strongly attracted to porch lights.  Mosquito Hawks. Mosquito hawks are colloquial terms for crane flies and dragonflies. These insects received this nickname because they are perceived to eat mosquitoes, making them a beneficial insect. Mosquito hawks also received the term because they look like an oversized mosquito. This is particularly the case with the crane fly. The image to the left is a crane fly. While crane flies do not bite humans, they are potential threats to your lawn in large numbers. One of the fun summer events is the formation of dragonfly swarms throughout our area, and they are especially enjoyable when close to home, as in our backyards. There are many more dragonflies (called mosquito hawks by many) in summer, in part because they have been breeding successfully so the population builds. Many adults have arrived by migrating back to our neighborhoods, thus supplementing the home-grown numbers.
http://www.answers.com/Q/Is_the_mosquito_hawk_the_same_as_a_dragonfly http://a-mosquito.com/mosquito-hawk.php https://answers.yahoo.com/question/index?qid=20070701213307AArAK6C http://a-mosquito.com/mosquito-hawk.php http://fusionanomaly.net/dragonfly.html http://www.orkin.com/other/dragonflies/ http://www.mosquito.org/mistaken-identities http://www.mosquitoinfo.info/mosquito-hawks/ http://www.loyno.edu/lucec/natural-history-writings/dragonfly-swarms-summer-delight
why are dragonflies called mosquito hawks