Scientists who study insects (there are close to a million that can be studied!) are called entomologists. Why are they not called insectologists? Well, in a way they are. The word insect comes from the Latin word insectum, meaning cut up or divided into segments. (The plural of insectum, namely insecta, is used by scientists as the name of the taxonomic class that insects belong to.) This Latin word was created in order to translate the Greek word for insect, which is entomon. This Greek word also literally means cut up or divided into segments, and it is the source of the word entomology. The Greeks had coined this term for insects because of the clear division of insect bodies into three segments, now called the head, thorax, and abdomen.

Did you mean ontological?