Approximately 1,800,000 specimens are held, representing more than 100,000 species. PERC continues to actively grow. Through collecting, donations, and exchanges, an average of 15,000 specimens are added each year. The majority of specimens are pinned and housed in standard USNM drawers. A sizable number of specimens or parts thereof are maintained on microscope slides, and an extensive and rapidly growing collection of alcohol-preserved material is also housed.

Although taxa are broadly represented geographically, approximately 65% of the specimens are from Indiana, and PERC is by far the single most important resource center for the insects of Indiana. PERC is recognized internationally as a primary resource in several areas:

• Primary and/or secondary type specimens for some 2,350 species, including the majority of types of W. S. Blatchley, G. F. Edmunds, Jr., and W. P. McCafferty.
  
  
• The Coleoptera holdings based on the collections of W. S. Blatchley, R. Everly, R. Arnett, F. Young, N. M. Downie, and others.
  
  
• The L. Chandler bee collection.
  
  
• The aquatic insect collections, which are becoming one of the most important in North America. Most notable is the mayfly collection, which is the largest and most comprehensive collection of Ephemeroptera in the world.