Pepsis elegans Lepeletier (Hymenoptera: Pompilidae: Pepsinae)—a secretive spider wasp and century-long conundrum

Abstract

After 105 years of study and 425 recent natural photographs, the host spider and nesting behavior of Pepsis elegans Lepeletier (Hymenoptera: Pompilidae: Pepsinae) remain a mystery. Pepsis elegans is the only species in the large and impressive genus Pepsis Fabricius that lives east of the Mississippi River, mainly in the southern U.S. The other 14 Nearctic Pepsis species inhabit the southern U.S. west of the Mississippi River and northern Mexico. They capture and provision their nests with large, hairy, heavy-bodied, stout-legged tarantulas of the genus Aphonopelma Pocock (Araneae: Mygalomorphae: Theraphosidae), the only native theraphosid genus in this region. There are no tarantulas east of the Mississippi River, except in East Baton Rouge Parish, LA, and no valid host spider records or nesting biology information for P. elegans, the largest spider wasp in the eastern US. Rau and Rau’s (1918) questionable field observation of this secretive, dark, violaceous-winged spider wasp yielded no nest, host spider or wasp specimen, and only initiated questions about its identification and nesting biology. The method of host spider transport, as described in Rau and Rau’s (1918) observation, is identical with that of Entypus fulvicornis (Cresson) (Hymenoptera: Pompilidae: Pepsinae), a species similar in size and color to P. elegans and often misidentified as such and vice versa. Potential host spider for P. elegans may include cork-lid trapdoor spiders in the genus Ummidia Thorell, especially U. audouini (Lucas) (Araneae: Mygalomorphae: Halonoproctidae). This spider is abundant, size¬able, and stout enough to provide sufficient food for the developing P. elegans larva. The genus Ummidia and P. elegans have nearly identical geographic location maps and occur in the same habitat. Pepsis elegans could conveniently use the spider’s burrow as a nest without having to excavate one from the ground surface and be detected by the burrowing activity or lengthy, arduous, and cumbersome host spider transport. Pepsis elegans females from various localities had dried mud on the forewings and body inferring they were underground in moist, fine-grained soil as in a burrow. Females were active at night introducing the possibility of cryptic nocturnal nesting, as in some other Pepsis species. Ummidia audouini is nocturnally accessible in its burrow entrance, holding the trapdoor slightly ajar as it waits in the darkness to ambush unsuspecting prey. Punzo’s (2005) study of the closely related, orange-amber-winged, southwestern U. S. and Mexican P. cerberus Lucas is questionable based on the spider misidentification, possible wasp misidentification, and incompatible spider wasp-tarantula size difference. The host of P. cerberus and P. novitia Banks, a possible P. cerberus × P. elegans hybrid (Hurd 1952), is likely the southwestern wafer-lid spider Eucteniza relata (O. P.-Cambridge) (Araneae: Mygalomorphae: Euctenizidae) (Gillaspy 1990) and not Aphonopelma as indicated by Punzo (2005).

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