Megischus bicolor, or "Crown of Thorns" wasp, is a species of wasp within the family Stephanidae (order Hymenoptera) that parasitizes wood-boring beetle and wasp larvae, specifically jewel beetle (family Buprestidae) and siricid wasp larvae. This species is found throughout the United States and northern Mexico and is one of only two Stephanid wasp species that are found in eastern North America (the other being Megischus brunneus which is less common in New England) and prefers coniferous and mixed woodlands. The term bicolor refers to the two morphs of this species with one having a uniformly black colored head and pronotum, and one having a brownish-red head and black pronotum.
A uniformly black Megischus bicolor specimen. Notice the "crown of thorns" on the head and enlarged hind femora.
Megischus bicolor is considered a "rare" species in that it is not commonly found by the general onlooker but can be found through lots of dedicated sweep netting, especially up at the fields of Dyce Lab in Sapsucker Woods, three miles north of Cornell in late summer-early fall. It has also been rumored that this species is attracted to blue objects and there are multiple reports of collectors using blue bowls containing a soap solution to capture them.
A 1918 Megischus bicolor specimen from the Cornell University Insect Collection
Stephanid wasps are characterized by a circular set of projections that form a "crown" on their head, hence the name "crown wasp." It is believed that these projections are used to aid in emergence from pupal chambers within wood. Other defining characteristics include an elongated neck and highly modified hing legs with swollen femora. Originally grouped within the family Ichneumonidae due to their similar appearance and pronounced ovipositor, stephanids were placed into their own family in 1839 and eventually were given their own superfamily, "Stephanoidea," in 1949.
The Cornell University Insect Collection only has one drawer containing Stephanid wasps as they are very rare and difficult to find. There are thirteen Megischus bicolor specimens total, shown in the bottom right.
References: Aguiar, A., 2005 Stephanoidea: Stephanidae. [WWW Document]. URL <http://tolweb.org/Stephanidae> (accessed 11.2.17) Aguiar, A., Deans, A., Engel, M., 2013 Order Hymenoptera. In: Zhang Z-Q (ed) Animal Biodiversity: An outline of higher-level classification and survey of taxonomic richness Zootaxa, 3703, pp. 51-62.