When selecting a textbook, college instructors must weigh a variety of factors. One is whether the text is written at a level that is accessible to one's students. An important factor in this is how many technical words are used. I developed an index to calculate logodiversity, a term I coined that reflects the number of technical words and the usage frequency of those words. The college-level animal behavior textbooks I examined varied greatly in their logodiversity. A fairly reliable substitute for the more time-consuming calculation of logodiversity is the ratio of pages in the glossary to the number of pages in the text as a whole. (Contains 1 table and 4 figures.)