Mosquitoes are insects which make up the family Culicidae. They have a pair of scaled wings, a pair of halteres, a slender body, and long legs. The females of most mosquito species suck blood (hematophagy) from other animals, which has made them the most deadly disease vectors known to man, killing millions of people over thousands of years and continuing to kill millions per year by the spread of diseases. Length varies but is rarely greater than 16 mm (0.6 inch), and weight up to 2.5 mg (0.04 grain). A mosquito can fly for 1 to 4 hours continuously at up to 1–2 km/h travelling up to 10 km in a night. Most species are nocturnal or crepuscular (dawn or evening) feeders. During the heat of the day most mosquitoes rest in a cool place and wait for the evenings. They may still bite if disturbed.