The Trogidae is a small family (about 300 species worldwide) that occurs on all
major continents. Members in the family are easily recognized by their overall
warty, brown to gray to black, dirt-encrusted appearance, and their flat abdomen.
The family includes three genera. The genus Trox is widespread in the
Holarctic and Ethiopian regions, the genus Omorgus occurs primarily in
arid regions in the southern continents, and the genus Polynoncus occurs
throughout South America. Adults and larvae can be found on the dry remains of
dead animals (they are usually among the last of the succession of insects that
invade carcasses) or in the nests of birds and mammals where they feed on hair,
feathers, and skin.
Length 2.5-20.0 mm. Shape oblong-oval, convex. Color brown or gray to black, often
with short, moderately dense, gray or brown setae; dorsal surface often greasy
or encrusted with dirt. Head deflexed. Antennae 10-segmented with 3-segmented,
opposable club (all segments tomentose); basal segment of antenna robust. Eyes
with variable ommatidia (eucone, duocone, and exocone), not divided by canthus.
Clypeus lacking tubercle or horn. Labrum truncate, not projecting beyond apex
of clypeus. Mandibles with mandibular brush and prostheca, projecting weakly beyond
apex of clypeus. Maxillae with 4-segmented palpi; labium with 4-segmented palpi.
Pronotum short, broad, convex; sculptured with ridges, depressions, or tubercles;
with or without setae. Elytra convex with striae impressed and intervals ridged
or tuberculate. Pygidium concealed by elytra. Scutellum exposed; shape hastate
or oval. Legs with coxae transverse, mesocoxae contiguous or nearly so; protibia
more or less slender, outer margin weakly toothed, apex with one spur; meso- and
metatibia with 2 apical spurs; spurs mesad, adjacent (not separated by basal metatarsal
segment); profemora enlarged (concealing or partially concealing head when deflexed);
meso- and metafemora not enlarged; tarsi 5-5-5; claws equal in size, simple; empodium
absent. Abdomen with 5 free sternites; 7 or 8 functional abdominal spiracles situated
in pleural membrane. Wings well developed, M-Cu loop present, with 1 or 2 apical
detached veins. Male genitalia trilobed. References: Cooper 1983; Scholtz 1986,
1990a. Keys: Vaurie 1955, Scholtz 1990b.
The Trogidae is considered either as a family within the Scarabaeoidea or as a
subfamily of the family Scarabaeidae. This work follows Scholtz 1986) and Lawrence
and Newton (1995) who treat the Trogidae as a family. Monophyly of the Trogidae
is suggested by the fact that all larvae share well developed, lateral ocelli
(unique in the Scarabaeoidea). The group is generally regarded as among the primitive
groups of scarabaeoids (e.g., Crowson 1954, 1981) based on the trilobate form
of the male genitalia. According to the phylogenetic analysis of Browne (1993),
the Trogidae is a member of a clade that includes the Glaphyridae, Pleocomidae,
and Bolboceratinae (Geotrupidae).
In the New World, three genera are known (Scholtz 1982).
New World Genera of Trogidae
Omorgus Erichson 1847
Polynoncus Burmeister 1876
Trox Fabricius 1775
Trogids are most diverse in the temperate and subtropical regions and are most
common in drier habitats. Adults and larvae are among the last scavengers that
visit the dry remains of dead animals where they feed on feathers, fur, and skin.
They also feed on organic matter found in nests of mammals and birds (i.e., feces,
feathers, and fur). Many species are attracted to lights at night. The life histories
of many species remain poorly known because of specialized associations with bird
nests and mammal nests. Much biological data could be gathered by collecting from
burrows and nests. When disturbed or frightened, adults feign death and remain
motionless. This, in combination with their dirt-encrusted appearance, enables
them to evade potential predators that might be scavenging at a carcass. Because
organic debris and soil often adhere to the surface of these beetles, cleaning
is necessary in order to see important characters such as sculpturing and setae.
Adults stridulate by rubbing a plectrum (located on the penultimate abdominal
segment) against a file (located on the internal margin of the elytra) (Lawrence
and Britton 1991). Larvae of carcass-feeding species live in short, vertical burrows
beneath the carcass (Baker 1968). Larvae do not stridulate.
Form scarabaeiform (c-shaped, cylindrical). Color creamy-white or yellow (except
at caudal end which may be darkened by accumulated feces). Cranium heavily sclerotized,
brown to black. Antennae 3-segmented with apical segment much reduced. Lateral
ocelli present. Frontoclypeal suture distinct or faint. Labrum bilobed. Epipharynx
with an oval pedium often surrounded by phobae; heli absent, tormae united. Maxilla
with galea and lacinia distinctly separate; maxillary stridulatory area with a
row or patch of minute teeth; maxillary palp 4-segmented. Abdominal segments 1
to 6 with 3 annuli, each with one or more transverse rows of short, stiff setae.
Spiracles with closing apparatus; cribriform or biforous. Ventral surface of last
abdominal segment with bare, fleshy lobes surrounding anus. Legs 4-segmented,
well developed, lacking stridulatory apparatus, each with a long, curved claw
that has 2 setae at its base. References: Ritcher 1966, Baker 1968, Scholtz 1990
BAKER, C. W. 1968. Larval taxonomy of the Troginae in North America
with notes on biologies and life histories (Coleoptera: Scarabaeidae). United
States National Museum Bulletin 279: 1-79.
BROWNE, D. J. 1993. Phylogenetic significance of the hind wing basal
articulation of the Scarabaeoidea (Coleoptera). Ph.D. Thesis, University of Pretoria,
Pretoria, South Africa.
COOPER, J. B. 1983. A review of the Nearctic genera of the family
Scarabaeidae (exclusive of the subfamilies Scarabaeinae and Geotrupinae) (Coleoptera),
with an evaluation of computer generated keys. Doctoral Thesis, Department of
Biology, Carleton University, Ottawa, Ontario, Canada. 1121 pp.
CROWSON, R. A. 1954 (reprint 1967). The Natural Classification
of the Families of Coleoptera. E. W. Classey, Middlesex, England. 214 pp.
CROWSON, R. A. 1981. The Biology of Coleoptera. Academic Press,
New York. 802 p.
LAWRENCE, J. F. and E. B. BRITTON. 1991. Coleoptera. The Insects
of Australia, 2nd edition, Volume 1, , pp. 543-683. Melbourne University Press,
LAWRENCE, J. F. and A. F. NEWTON, JR. 1995. Families and subfamilies
of Coleoptera (with selected genera, notes, and references and data on family-group
names), pp. 779-1006. In J. Pakaluk and S. A. Slipinski (eds.), Biology, Phylogeny,
and Classification of Coleoptera. Papers Celebrating the 80th Birthday of Roy
A. Crowson. Muzeum i Instytut Zoologii PAN, Warszawa, Poland.
RITCHER, P. O. 1966. White Grubs and Their Allies: A Study of
North American Scarabaeioid Larvae. Oregon State University Press, Corvallis,
Oregon. 219 pp.
SCHOLTZ, C. H. 1982. Catalogue of the world Trogidae (Coleoptera:
Scarabaeoidea). Republic of South Africa, Department of Agriculture and Fisheries,
Entomology Memoire 54: 1-27.
SCHOLTZ, C. H. 1986. Phylogeny and systematics of the Trogidae (Coleoptera:
Scarabaeoidae). Systematic Entomology 11: 355-363.
SCHOLTZ, C. H. 1990a. Phylogenetic trends in the Scarabaeoidea (Coleoptera).
Journal of Natural History 24: 1027-1066.
SCHOLTZ, C. H. 1990b. Revision of the Trogidae of South America
(Coleoptera: Scarabaeoidea). Journal of Natural History 24: 1391-1456.
VAURIE, P. 1955. A revision of the genus Trox in North
America. Bulletin of the American Museum of Natural History 106: 1-89.