A fundamental relationship between insects and humans revolves around those insect species that transmit diseases of humans. Almost all mammals are fed upon by some arthropod parasite with the exception of whales, dolphins, and manatees. It is estimated that at least one of every six humans is suffering from some insect-carried disease.

Human blood is a primary meal for many of our arthropod parasites, such as mosquitoes, ticks, and lice. Parasites usually have specialized mouthparts and feeding mechanisms. For example, mosquitoes have straw-like mouthparts, including two long sharpened stylets that pierce the skin and four stylets that form a channel through which blood is sucked up. (View an animation of a mosquito biting.)

Except for the inconvenience of having an itchy welt at the site of the bite, most people do not have a problem with a mosquito bite. The more important issue concerns what other organisms the insect may be carrying that might enter the human's bloodstream, possibly causing sickness and sometimes death.

Insects serve as vectors, or carriers, for several major human diseases, including

• malaria
• yellow fever
• African sleeping sickness
• bubonic plague
• West Nile virus

Several disciplines including medicine, epidemiology, and immunology interact with entomology in the study of these insect-vectored diseases.