Although it may not be apparent immediately, entomology and chemistry are tightly connected. The insect body is made of chemical substances. Insects use chemicals to communicate information to each other, to defend themselves against enemies, digest food, and much more. Humans also use chemicals in their interactions with insects. Chemical insecticides are used to control agricultural pests, and fight against annoying, parasitic, and disease-transmitting insects. Insect products are utilized in food, pharmaceuticals, and textiles. Chemicals are used in our studies of insects. Chemical Abstracts Service databases contain chemical and chemistry-related information on more than 170,000 living organisms, including more than 20,000 insects. This information, available for online search and retrieval using several CAS tools, such as STN on the web, STN Express, and SciFinder, can serve as an invaluable resource for entomologists.