Coelichneumon Thomson, 1893

Coelichneumon is a diverse genus comprised of around 190 species that occurs worldwide except for subsaharan Africa, but is most diverse in the Holarctic region (temperate areas of North America and Eurasia). In the tropics, Coelichneumon is typically restricted to higher elevation sites. With 50 described species, Coelichneumon is one of the most diverse Nearctic ichneumonine genera. There are likely a considerable number of undescribed species, particularly in the West.

Most Coelichneumon species, and especially Neactic species, are medium-sized and iridescent blue with yellowish-white markings. However, there is a range in coloration, with some species having iridescent red or purple colors, or are plain black without any iridescence.

Structurally, Coelichneumon is characterized by the sloping propodeum (without distinct dorsal and posterior faces), with an elongated second lateral area. Additionally, the gastrocoeli are unusually deep and the thyridia are well developed and wider than the interthyridial width. In field photos, these characters are usually not visible, but an identification can usually be confirmed by the dorsally rounded metasomal tergites which differentiates Coelichneumon frrhingom similarly colored Cratichneumon or Ctenichneumon species.

Coelichneumon is closely related to Protichneumon, though the two can easily be differentiated as Protichneumon species are usually larger with a black mesosoma and a brownish-red metasoma.

Diagnosis

• propodeum sloping (without distinct dorsal and posterior faces) and with an elongated second lateral area
• gastrocoeli deeply impressed
• thyridia wider than interthyridial width
• female metasomal apex oxypygous
• color typically black or iridecent blue with yellowish-white markings