Female, CNC, UNITED STATES. Holotype locality: Mount Evans, 3,658m, Clear Creek County, Colorado, USA.

First label: Mt. Evans, COLO./12,000’ 3 Aug./W.R.W.Mason ‘61. Second label: MIC CNC666529.

1 ♀, 2 ♂ (CNC). Same locality than holotype, but collected at altitudes ranging from 4,023m (female) to 4,267m (males); collecting dates from 25.vii–4.viii.1961.

This species can be separated from all other described species of Microplitis in North America by the combination of the following features: small size (body length 2.0–2.1 mm, fore wing length 1.7–1.8 mm), entirely dark brown to black coloration (including all legs), slightly infumated wings, very short antenna (its length not surpassing the length of mesosoma), apical flagellomeres cubic (about as long as wide), and high altitudinal distribution.

Body dark brown to black (except for metatibia and al tarsi light brown). Wings slightly infumated, veins and pterostigma mostly brown. Head and mesosoma (dorsally) finely sculptured, metasoma mostly smooth dorsally, except for finely sculptured T1. Ovipositor sheaths smooth, almost without setae. Head not elongate; malar line shorter than mandible base; labrum, mandibles and glossa not enlarged; antennal flagellomeres 14–15 cubic (about as long as wide). Hypopygium not elongate and not projecting beyond last tergum. Ovipositor sheaths relatively very small, barely visible beyond hypopygium. Fore wing with vein R1 much shorter than pterostigma. Legs with tarsal claws simple. Body measurements (mm). Body L: 2.1 (2.0); fore wing L: 1.8 (1.7); ovipositor sheaths L: 0.15 (approximate measurement); metafemur L/W: 0.59/0.15; metatibia L: 0.77; metatibia inner/outer spurs L: 0.13/0.12; first segment of metatarsus L: 0.33; F1/2/3/14/15/16: 0.14/0.11/0.10/0.07/0.07/0.11; ocular–ocellar line: 0.13; interocellar distance: 0.09; posterior ocellus diameter: 0.04.

Males. As females but with antenna of more normal length.

United States: CO.

From the Latin adjective ‘altissimus’, meaning ‘the highest’, referring to the locality at which all specimens were collected, currently the highest altitude of any known species of Microgastrinae in North America.

No biological or molecular data is known for this species. The small body and wings size, reduced antenna and short flagellomeres, and the dark coloration are all adaptions to living in a very cold, windy and harsh environment such as Mount Evans. The two male speciens were collected at 4,267m, by far the highest altitude recorded for any Microgastrinae in North America.