DISTINGUISHING CHARACTERS: Body length about 1.0 to 9.0 mm, robust and stout to slender and elongate; usually black, brown and/or yellow (only species of Chryseida are metallic coloured: blue-green, often with reddish or bronzy cast), strongly sclerotized, sculpture usually umbilicate, but may be finely transversely reticulate (e.g. Rileya spp.) to nearly smooth (some Systole spp.). Antenna 9-13 segmented, inserted about midway between the mouth and anterior ocellus; male antenna often with whorls of long trichoid sensilla (setae) or at least with a variously expanded ventral plaque on scape, or sometimes both (some Eurytoma, Aximopsis, etc.). Pronotum in dorsal view broadly, transversely rectangular to quadrate; mesoscutum with notauli complete, often deep. Fore wing with marginal vein generally longer than stigmal vein, postmarginal vein always present but sometimes quite short. All tarsi 5-segmented (except males of Boucekiana). Gaster very rarely broadly joined to the propodeum, petiole elongate to inconspicuous; gaster often somewhat laterally compressed and circular, oval or acuminate in lateral view, sometimes dorsoventrally flattened; usually smooth, shining, and non-collapsing; ovipositor usually hidden, not prominent (some Bephratoides with ovipositor sheaths exserted).

MOST OFTEN CONFUSED WITH: Pteromalidae. The most distinctive character of eurytomids is the quadrate to rectangulate pronotum in dorsal view. Most eurytomids have umbilicate sculpture on the mesosoma, while most pteromalids have the pronotum transversely and lack umbilicate sculpture. In a few groups of pteromalids the pronotum may be elongate, but if so it is metallic blue or green, and generally longer than wide. In eurytomids the abdomen is generally somewhat laterally compressed (generally not dorsoventrally compressed, except some Neorileya species and males of Rileya) and circular to oval in profile. In pteromalids the abdomen is usually dorsoventrally compressed and somewhat triangular in outline.

CLASSIFICATION & DISTRIBUTION: The Eurytomidae has a cosmopolitan distribution and contains about 1400 nominal species in 87 genera (Noyes 1998) worldwide. Although the family has been divided into as many as seven subfamilies (Burks 1971; Zerova 1988), or into several tribes (Subba Rao 1978), there is little evidence that these groups are monophyletic, with the exception of Rileyinae s.s. (Gates, Ph. D. dissertation 2000) and most likely Heimbrinae, excluding Heimbrella (Stage & Snelling 1986). There are currently three subfamilies are recognized (Stage & Snelling 1986; Boucek 1988): Heimbrinae (New World), Rileyinae (cosmopolitan) and Eurytominae (cosmopolitan). All Rileyinae (with a few exceptions: Platyrileya, Dougiola, Austrophotismus) share the following synapomorphies (unique features): 1) 2-3 anelli, small ring-like segments at the base of the flagellum; 2) highly reduced prepectus, an independent sclerite between the wing base and pronotum laterally; and 3) anterior gastral terga foreshortened, often reduced to flap-like structures. Additionally, Rileya + Platyrileya share a unique tongue-in-groove junction between the mesepimeron and metapleuron while all rileyines have variously produced costulae (transverse ridges) on the propodeum and lack any type of median channel or groove. The Heimbrinae are distinct from all other eurytomids in that they possess both a carapace-like (fusion of terga 2+3) gaster and scutellar spine. There is currently no support for a monophyletic Eurytominae as all potential synapomorphies to date have proven homoplastic. NOTE: The generic classification within Eurytomidae is in desperate need of revisionary work in order to ascertain which nominal genera merit this rank and which are synonymous. This primarily involves Eurytoma and related taxa (i.e. Prodecatoma, Philolema, Mesoeurytoma, Aximopsis, etc.) and the character intergradation between them.

TAXONOMY: Francis Walker (1833) originally recognized four genera of Eurytomidae when he characterized the family: Eurytoma, Decatoma, Isosoma and Systole. Ashmead (1904) designated 23 new genera and five tribes: Aximini, Eurytomini, Isosomini, Rileyini and Decatomini, which were accepted by Schmiedeknecht (1909) and Bugbee (1936). The tribes were elevated to subfamily status (Ferriére 1950) and maintained by subsequent authors (Nikol’skaya 1952, Claridge 1961a). Burks (1971) proposed three additional subfamilies: Heimbrinae, Prodecatominae and Philoleminae, although he did not provide any characters to distinguish these groups. Eurytomid subfamily classification was further destabilized: Peck’s catalog of Nearctic Chalcidoidea (1963) recognized five subfamilies, Krombein et al. (1979) accepted six subfamilies, Riek (1970) and Stage & Snelling (1986) only three and, Zerova (1988, 1995) proposed seven and five, respectively. Unlike most other works, the latter three references provided some morphological justification for reported subfamilial classification. Only Rileyinae is considered as distinct by all authors.

Peck, Boucek and Hoffer (1964) recognized only two subfamilies: Rileyinae and Eurytominae. They reasoned that only these two taxa had characters explicit enough to merit subfamily rank. Stage & Snelling (1986) agreed with this assessment although they recognized Heimbrinae based on a comparative morphological study. The three subfamily arrangment solves character intergradation problems superficially, but greater uncertainty is created concerning monophyly of Eurytominae.

FOSSIL HISTORY: The Chalcidoidea are thought to have originated from an ancestral eurytomid/torymid groundplan (Malyshev 1968). Yoshimoto (1975) states that this ancestor may have given rise to at least two major lines: 1) a chalcidid-pteromalid groups with 5 tarsomeres and 13 antennal segments and 2) a trichogrammatid-eulophid lineage with 3-5 tarsomeres and 4-10 antennal segments. Eurytomidae are hypothesized to have originated at least during the late Cretaceous period as supported by the existence of the fossilized extant genera Decatoma (now =Sycophila) and Eurytoma from the Miocene and Oligocene strata in modern Colorado and Wyoming, dated at 13-40 million years old (Brues 1910). Some modern chalcidoid families (Eulophidae, Tetracampidae, Mymaridae, Ormyridae) had already differentiated by the Late Cretaceous (Rasnitsyn 1975) and thus are assumed to have been in existence during the Early Cretaceous. Additional modern chalcidoid families (Torymidae, Pteromalidae, Perilampidae, Eupelmidae, Agaonidae, Chalcididae) are known from 35-50 million year old Oligocene Baltic amber (Brischke 1886, Helm 1899, Trjapitzin 1963) and Miocene Florrisant shale (Brues 1910). If it is assumed that eurytomid evolutionary rates correspond to those of other chalcidoid families based on fossil evidence, then the Early Cretaceous may have seen the most rapid eurytomid diversification, though there is no fossil evidence to support this claim (Zerova 1988). Early eurytomid forms were associated with larvae or insect eggs inside angiosperm stems (Zerova 1988, 1992) providing a trophic link between eurytomid evolution and the Angiosperm radiation of the Cretaceous (Zerova 1992).