The genus Temnostoma includes relatively large species that mimic hornets (Vespinae) and mason wasps (Eumeninae). The thorax is matte black with yellow or light-gray pollinose markings and spots. The abdomen segments have one or two transverse bands that can be yellow or white. Front legs are black. When threatened or in flight, the flies extend their black forefeet in front of their heads and wave them, imitating the antennae of wasps. Species in the genus Temnostoma differs from the related genus Spilomyia by the lack of spurs on the rear legs, the yellow transverse bands of the legs resulting from dusting (micro-hair), and unmarked eyes. Falsehorns occur in moist woodland with mature stands of deciduous trees such as maple, birch, and aspen. Larvae are found in decaying wood.

The genus includes a total of twenty-three species, eight of which are found in North America. Five species are known from Minnesota.

Key to the species

  1. – Yellowjacket mimic. Abdomen banding consists of a pair of yellow bands (or solid color) … 2
    1′. – Mason wasp mimic. Abdomen banding consists of a single yellow or white band along the anterior edge of each segment … 3
  2. – Yellow bands enclose a pair of black rectangles on the 4th and 5th abdomen segments … Temnostoma excentrica
    2′. – Yellow triangle on thorax above scuttelum … T. alternans
  3. – Wings with several basal cells clear, free from hair … 4
    3′. – Wings without clear cells, completely trichose … T. trifaciatum
  4. – Pair of faint, pollinose spots on thorax above scuttelum. Bare metasternum. Black setae on black portion of final abdominal segment. Wing cells clear or partly clear … T. barberi
    4′. – Yellow setae on black portion of final abdominal segment. Metasternum with hair. Without pollinose spots on thorax above scuttelum … T. balyras
Bare-bellied Falsehorn (Temnostoma barberi) – Rice County – June 12, 2018
  • Temnostoma alternans Loew 1864 – Wasp-like Falsehorn
  • Temnostoma apiforme (Fabricius, 1794) ? –
  • Temnostoma balyras (Walker 1849) – Yellow-haired Falsehorn
  • Temnostoma barberi Curran 1939 – Bare-bellied Falsehorn
  • Temnostoma excentrica (Harris 1862) – Black-spotted Falsehorn
  • Temnostoma obscurum Loew 1864 – Hairy-winged Falsehorn
  • Temnostoma trifasciatum Robertson 1901 ? – Three-lined Falsehorn
  • Temnostoma venustum Williston 1887 * – Black-banded Falsehorn