Natural History & Behavior

Prey-carrying mechanisms vary considerably throughout the family (Evans 1962b). Pompilids transport their prey in a specific manner by holding a certain part of the spider’s body. Transportation is achieved by pulling, pushing, carrying, or flying with the spider (Evans & Yoshimoto 1962). Auplopus and related genera have apparently streamlined transport by amputating the legs of their hosts (Evans 1953, Evans & West-Eberhard 1970). These authors proposed aprey-transport etho cline in which dragging prey blindly backwards represents the ancestral condition, with several steps leading to the most derived condition of the wasp amputating the legs of its prey and flying forward with the spider under its body.

Pompilids also vary in where they choose to locate a nest. Many spider wasps nest in the ground, some in preexisting cavities, others dig their own nest. Most pompilids prepare only a single cell per nest. However, some species make multiple cells per nest.

Several genera have evolved alternate nest types, such as Sphictostethus that nest in logs, Ageniellini species such as Auplopus that make aerial nests of mud, and at least one Priochilus that makes nests of masticated leaves. Most have a modified mentum with stout bristles to carry materials. These nest types also suggest a linear pro gression from simple to complex, leading Evans and Shimizu (1996, 1998) to propose an ethocline of aerial nest construction and communal nesting: the ancestral condition of digging a burrow with mandibles led to several intermediate steps and eventually to the derived condition of building mud cells above ground. The evolution of such aerial nesting could be an important precursor to parasocial behavior, by concentrating females and forcing interactions at limited, suitable nest sites (Starr 1991).

Pompilid nesting patterns also vary in the timing of hunting in relation to nest building. Most females hunt their prey first, then find or prepare a nest, but some species prepare a nest before hunting. The latter seems selectively advantageous over the former, in reducing the need to hide or protect prey from predators or other wasps such as clepto parasitic Ceropales, Evagetes, Aridestus, and likely Psoropempula that steal prey from other pom pilids (Evans 1966a, 1974; Evans & West-Eberhard 1970; O’Neill 2001). Evagetes seeks and parasitizes a provisioned pompilid nest, while Ceropales finds a paralyzed spider left unattended by another female busy preparing a nest (Shimizu 1994).

Evans (1953) synthesized much of the variation in pompilid behaviors associated with building and provisioning a nest, including the sequences in which they are performed. Based on his views of pompilid relationships, Evans (1953) hypothesized stepwise evolution between different states of nesting, with behaviors evolving from simple to complex, and certain reversals back to (simple) ecto- and cleptoparasitism. This nesting-sequence ethocline has been presented as a likely model of behavioral evolution leading to sociality (e.g., Evans & West-Eberhard 1970).