Entomology is the scientific study of insects. Insects have many kinds of interactions with humans and other forms of life on earth, so it is an important specialty within biology; unlike many other fields of biology, entomologists include both persons studying insects for their own sake, and those employed by commercial concerns interested in the control of insects (usually pest species). This divides the field into basic and applied entomology.
Because of this divide, any given university might put their department of entomology in either the biology department (with an emphasis on basic entomology) or in the agriculture department (with an emphasis on applied entomology. Despite this difference, today many entomology groups study both basic and applied aspects of the science.
The definition of entomology, especially as far as entomology departments is concerned, is sometimes widened to include the study of other terrestrial arthropods, such as spiders, scorpions, and ticks (the arachnids).