Dryinids are parasitoid wasps with larvae that infect auchenorrhynchs (Guglielmino & Olmi, 1997). The adult wasps can sometimes be predaceous: the last segments of many dryinid females have long spines on them used to impale prey. These aren’t just the typical parasitoid wasp, they can be active predators.
Within the Chrysidoidea, it is agreed that they are the sister group to the Embolemidae, with their similar choice of host being one of the synapomorphies. Only one study that I am aware of, Rasnitsyn (1988), has rejected this relationship, but his analysis was shown to be flawed by Carpenter (1990) – Rasnitsyn had not considered all the phylogenetically relevant characters.
The family was last revised by Olmi (1984) with a supplement by Olmi (1989), but so many new species have been described since then that it is in need of revision. By rough count, I would say that by now, the species numbers stand at ~1400 species in ~35 genera in ~10 subfamilies.
They’re highly-specialised and distributed worldwide. They are instantly recognisable by the chelate (claw-like) front legs: they have a pretarsal ungue interacting with a large projection on the fifth tarsomere. They’re used are used to grab the host when ovipositing. It’s an apomorphy for the Dryinidae family, but it’s plesiomorphically absent in the basalmost subfamily (the Aphodinae).
Dryinids are unique among hymenopteran endoparasitoids in that one species practices ovicide, a strategy common in ectoparasitoids (Mayhew, 1997) but very rare in endoparasitoids. The species it’s been documented in, Haplogonatopus atratus, uses its ovipositor to puncture eggs already laid in a host, regardless of whether the eggs are of the same species or not (Yamada & Kitashiro, 2002).
The purpose of ovicide is unknown, but it’s probably a space and resource thing. They don’t lay too many eggs, but those that are lain are done so in precise locations. Having additional parasitoids on the host would decrease the fitness of the larvae, so it makes sense to kill them.
Fossilwise, we have them preserved in both ambers and rocks (from Mongolia and Brazil, although these have variously been interpreted as members of other families; see Olmi et al. (2010)). The earliest dryinid comes from the Cretaceous amber of Lebanon (Olmi, 1999). There are at least 11 species in Dominican amber (Arillo & Ortuño, 2005) and one genus, Dryinus has 17 fossil species (Olmi & Guglielmino, 2011), so they do count as relatively abundant as far as fossil record goes. Pictured above is Deinodryinus velteni from the Baltic amber; notice the front leg and the spines at the back, the two distinctive features I mentioned.
Arillo A & Ortuño VM. 2005. Catalogue of fossil insect species described from Dominican amber (Miocene). Stuttgarter Beiträge zur Naturkunde B 352, 1-68.
Carpenter JM. 1990. Rasnitsyn on Chrysidoidea, or what is a cladist really? Sphecos 19, 7-9.
Guglielmino A & Olmi M. 1997. A host-parasite catalog of world Dryinidae (Hymenoptera: Chrysidoidea). Contributions on Entomology, International 2, 165-298.
Guglielmino A & Olmi M. 2011. Revision of fossil species of Deinodryinus, with description of a new species (Hymenoptera, Dryinidae). ZooKeys 130, 495-504.
Mayhew PJ. 1997. Fitness consequences of ovicide in a parasitoid wasp. Entomologia Experimentalis et Applicata 84, 115-126.
Olmi M. 1984. A revision of the Dryinidae (Hymenoptera). Memoirs of the American Entomological Institute 37.
Olmi M. 1989. Supplement to the revision of the world Dryinidae (Hymenoptera Chrysidoidea). Frustula Entomologica 12, 109-395.
Olmi M. 1999. New fossil Dryinidae from Baltic and Lebanese amber (Hymenoptera Chrysidoidea). Frustula Entomologica 21, 41-64.
Olmi M & Guglielmino A. 2011. Revision of fossil species of Dryinus belonging to lamellatus group, with description of a new species (Hymenoptera: Dryinidae). ZooKeys 130, 505-514.
Olmi M, Rasnitsyn AP & Guglielmino A. 2010. A Revision of Rock Fossils of Dryinidae and Embolemidae (Hymenoptera Chrysidoidea). Zootaxa 2499, 21-38.
Rasnitsyn A. 1988. An outline of the evolution of hymenopterous insects (Order Vespida). Oriental Insects 22, 115-145.