How to Recognize a Chalcid

In order to use this handbook it is necessary first to recognize a chalcidoid. One clue is their size. Rarely are specimens much over 5mm in length. In the field or the lab chalcidoids are most easily confused with small gnat like flies and other small wasps. Chalcidoids, being Hymenoptera, have two pairs of membranous wings as opposed to the single pair found in flies. Among the majority of wasps, chalcidoids are noted for their much reduced wing venation. In the forewing there are no cells that are completely surrounded by veins (see wing, p. 18; note that the "costal cell" has no vein on the forward edge). Most other Hymenoptera not only have several (or many) closed cells, but they have many veins on the wing as well. Chalcidoids have essentially only one vein that is branched at the end (into postmarginal and stigmal) and rarely not even this is branched. Among all wasps, chalcidoids are only likely to be confused with some of the proctotrupoid families (especially Scelionidae and Platygastridae) because the wing venation is similar. Here the distinctions become somewhat more difficult and technical. Most chalcidoids have a sclerite (side of mesosoma) called the prepectus between the base of the forewing and the pronotum, whereas proctotrupoids lack this sclerite. As a result, in most chalcidoids the base of the forewing appears to be removed some distance from the lateral corner of the pronotum, but in proctotrupoids the base appears to touch the corner of the pronotum. There is a technically more reliable character involving the position of the mesothoracic spiracle in chalcidoids (see Gibson 1993), but it is difficult to see and its use is seldom called upon, that it is of value mostly in esoteric cases of classification. Most Chalcidoidea also have elongate, raised sensilla on the antennae (usually seen as parallel white lines on the funicle segments), which proctotrupoids do not have. In the case of a few wingless chalcidoids, the spiracle and sensilla re the only technically accurate methods to separate them from the proctotrupoids. Finally, it should be noted that many chalcidoids tend to be metallic in coloration or to have mixtures of colors such as black and yellow. Proctotrupoids are never metallic and generally black. Although a difficult task at first glance, recognizing chalcidoids is not the impossible endeavor it may appear to be. With experience, chalcidoids may be identified to family level in the field and even on the wing. All it requires is a little practice.

Introduction to the Key

The key is designed to be "easy" to use, not necessarily absolutely technically or phylogenetically correct. It proceeds somewhat along the mental process we sue to sort chalcidoids to family, i.e., the easily observed characters are used first. The first alternative states the conspicuous character, and if you cannot see the character because the specimen is too small, it usually means you should take the second alternative. All known chalcidoid families (except for obscure Rotoitidae from New Zealand and Chile) are included (some as subfamilies). The key, however, is based on Nearctic species so that it will not work in all instances for Old World groups even at the family level. A few odd genera are keyed out near families other than the correct one because they appear aberrant (compared to the rest of the family) and generally cause a key to become filled with "either-or," and "if, and, or but" type statements. Generally, the families are fairly distinct morphologically (at least in one sex), but a few odd forms may cause a relatively simple key to become overly complex. Our feeling is that these few odd forms may be keyed out pragmatically (or learned by sight) and removed from the majority of species so the identification of remaining forms becomes possible without too much difficulty. We have tried to structure the key so that all common material will run through it. Many uncommon taxa should run through it as well. Male specimens of a few families (e.g., some eupelmids, pteromalids) will not run through the key. For males we've added additional comments in the discussion of Distinguishing Characters (not present in online version of key) to help. The illustrations for the key are rendered in large part by Linda Lawrence and Deborah Roney. A few drawings were borrowed (with modification) from sources listed in the text and under the taxon being identified.

Introduction to the Key Online

All text and drawings are taken from the original key:

Grissell, E. E., and M. E. Schauff. 1990. A handbook of the families of Nearctic Chalcidoidea (Hymenoptera).
Entomological Society of Washington (Washington, D.C.) Handbook 1:1-85.

Additional images for the key have been added by Dr Michael Gates at the USDA-ARS Systematic Entomology Laboratory (). Web work by Katja Seltmann with support from Andrew Ernst and Patricia Mullins at North Carolina State University (). This second version of the online key (third version of the key in total) was constructed using mx and linked to the Hymenoptera Anatomy Ontology .

Funding for this project has been in part from three National Science Foundation grants: Assembling the Tree of Life Project EF-0337220 for Building the Hymenopteran Tree of Life: Large Scale Phylogenetic Analysis of the Hymenoptera, Biological Databases and Informatics (BDI) Program DBI-0446224 for Morphbank: Web Image Database Technology for Comparative Morphology and Biodiversity Research and NSF DBI-0850223 for The Hymenoptera Ontology: Part of a Transformation in Systematic and Genome Science. This work is licensed under a Creative Commons Licence.

Printable Version

A PDF version of this key is available here