Black flies are common in humid, wooded regions in summer months and can be found throughout semitropical regions year round. Black flies are most active around sunset during June and July and act as severe nuisances to backpackers, hikers and other outdoor enthusiasts. Black flies are not active at night, nor do they live indoors.
Black fly larvae thrive in all kinds of flowing water, making them most common in creeks and waterfalls. Adults seek moist environments and may bite exposed skin such as the face. They may also find their way under belts and socks, although they are incapable of piercing through clothing. In order to avoid being bothered by black flies, hikers often tightly tuck in their shirts and pants.
These insects have proven to be such a nuisance in summer months that special hiking gear has been developed to combat them. Research also shows that black flies are more attracted to dark colors than to light colors; hikers who dress accordingly are less likely to be bothered.