Rhopalosomatidae

Definition

A small family of parasitoid wasps in the order Hymenoptera, comprising about 68 extant species classified in four genera (Rhopalosoma, Olixon, Paniscomima, and Liosphex) with worldwide distribution. Adults are typically nocturnal and weak-flying; larvae are ectoparasitoids of orthopteran nymphs, particularly crickets and wetas. The family is distinguished by reduced wing venation, a distinctively humped thorax, and elbowed antennae with a long scape. Three fossil genera are known from Cretaceous and Eocene deposits.

Etymology

From Greek rhopalon (club) + soma (body), referring to the clubbed or thickened body form characteristic of these wasps.

Example

Rhopalosoma nearcticum, a North American species in the family Rhopalosomatidae, parasitizes nymphs of camel crickets (Ceuthophilus) by attaching an egg to the host's integument; the larva feeds externally through several instars before dropping to the soil to pupate.

Related Terms

• Hymenoptera
• Parasitoid
• ectoparasitoid
• Olixon
• Rhopalosoma
• Orthoptera
• Vespoidea
• wing venation

Usage Notes

Sometimes grouped historically with Bradynobaenidae in the superfamily Vespoidea, though current phylogenetic studies place Rhopalosomatidae as a distinct lineage within Apocrita. The family is rarely encountered by collectors due to nocturnal habits and low population densities; specimens are most often collected at lights or by sifting leaf litter for host-associated larvae. Not to be confused with Rhopalidae (Hemiptera: true bugs), which share a similar root but are unrelated.