The Mediterranean Recluse Spider, Loxosceles rufescens (Dufour): An Abundant but Cryptic Inhabitant of Deep Infrastructure in the Washington, D.C. Area (Arachnida: Araneae: Sicariidae)

Loxosceles rufescens (Dufour), a relatively cosmopolitan, synanthropic species commonly known as the Mediterranean recluse spider, inhabits numerous government buildings in the Washington, D.C. area. Like the closely related brown recluse spider ( L. reclusa Gertsch and Mulaik ) in the south-central United States, L. rufescens can be extremely abundant with in a structure. Unlike L. reclusa , D.C. populations of L. rufescens are essentially troglophilic, concentrated mainly in basements, foundation walls, and other man-made subterranean habitats, typically in close association with Periplaneta americana (L.) and/or Reticulitermes spp. It has not been observed either outdoors or in smaller, residential buildings. Since this spider is often misidentified as L. reclusa by entomologists who are unaware of L. rufescens ' widespread distribution and potential for persistent and dense local populations, we present photographs to aid in distinguishing the adults of these two similar species.