Blue exoskeleton, aridity, and thermoregulation in some western Nearctic spider wasps (Hymenoptera: Pompilidae)

Several Nearctic spider wasp genera and subgenera in the subfamily Pompilinae (Hymenoptera: Pompilidae) in the arid western United States and northern Mexico are characteristically blue, violet, or purple in color: Aporus Spinola; Plectraporus Bradley; Chelaporus Bradley; Psorthaspis Banks; Chalcochares Banks; Evagetes Lepeletier; and Allochares Banks. Other genera and subgenera of Pompilinae in western U. S. and northern Mexico have one or more bluish or violaceous species: Episyron Schiødte; Notiochares Banks; Pompilinus Ashmead; Anoplius Dufour; Hesperopompilus Evans; Ammosphex Wilcke; and Arachnospila Kincaid. In California, 27/79 (34.2%) species of Pompilinae are blue, violet, or purple. The number of blue, violet, or purple Nearctic species in the subfamily Pepsinae in the western U. S. and northern Mexico is significantly fewer than in the subfamily Pompilinae. Only Pepsis Fabricius (Pepsini) and Auplopus Spinola and Ageniella Banks (Ageniellini) have bluish, bluish-green, greenish, or violaceous species. Black spider wasps predominate in the moist, densely vegetated, often forested, and mountainous areas of the eastern United States and Canada. Only 6/81 (7.4%) species of Pompilinae in the eastern U. S. and Canada are blue, violet, or purple. Four of the species are in the genus Evagetes.