However, female mosquitoes and black flies require blood in order to produce the next generation and some species will take it from people if they are available. Our breathing gives us away - they sense the carbon dioxide that we breathe out.
Mosquitoes breed in stagnant water. They pierce our skin and inject saliva which contains a substance that prevents clotting. The saliva actually causes the itch, not the bite. Some of the most aggressive mosquitoes that I encountered were in salt marshes.
Black flies breed in fast flowing water. They slice a hole in the skin and slurp up the blood from it. Their bite can be painful.
Ticks, which don't fly and aren't really an insect, also sense their host by its breath and also require blood to reproduce. Like mosquitoes and black flies, they also may transmit diseases. Ticks attach themselves to their victim's skin.
Horse and deer flies are larger biting flies. Unlike mosquitos and black flies, they don't seem to pay much attention to insect repellents. Their preferred victims are large animals such as deer or moose, but they will go after people, too.
Some insects, such as lady bugs, may also help control unhelpful insects. Dragonflies eat mosquitoes and other flies.
Honey bees produce honey.
Animated gif courtesy of Animation Factory
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