Martinez NJ, Franz NM, Acosta JA. 2009. Structure of the scarab beetle fauna (Coleoptera: Scarabaeoidea) in forest remnants of western Puerto Rico. Entomotropica 24(1): 1-9. We studied the richness and abundance of scarab beetle species (Coleoptera: Scarabaeoidea) in two successional forest fragments located on the campus of the University of Puerto Rico at Mayaguez (UPRM), western Puerto Rico. The sampling period extended from April to December, 2005, and included nine monthly repetitions of quantitative captures using necrophilous, pitfall, and light traps. A total of 2399 individuals pertaining to 14 species, or 36% of the Island’s total scarab diversity, were caught. The spatial variation in diversity and abundance was low among sites. However, there was a significant shift in community structure between the drier season (April to June) and rainy season (September to December). The following four species constituted 92% of all captured individuals: Canthochilum andyi Chapin, C. borinquensis Matthews, C. taino Matthews, and Phyllophaga vandinei Smyth. The results underscore the important role that western Puerto Rican forest fragments play in maintaining regional scarab beetle communities, and provide a baseline for developing ecological assessment tools for these habitats.