The MSB Division of Arthropods houses collections from the southwestern US as well as Central and South America and other areas of the world. Species concentrations are in Arachnida, Myriapoda, Coleoptera, Lepidoptera, and Orthoptera. The collection began with material from ecological research (including LTER sites and several NPS sites) and is now increasing its systematics focus. There are an estimated 200,000 specimens but many are still being integrated into the collection.