Bed bugs are small parasitic insects and are therefore animals. They are reddish brown in color and adults measure 4 millimeters to 6 millimeters, which is approximately the size of an apple seed.
Although they possess short, stubby wings, bed bugs are flightless insects. They are best known for feeding on sleeping humans, although they are a parasite of both birds and bats as well. They infest bedding, mattresses and other furniture, and they can also live on clothing.
The irritation caused by a bed bug bite is an inflammatory reaction to the bug's saliva after a bite, resulting in redness and itching.