Overview
The family contains more than 220 described species placed in 35 genera, including
those described in the following chapters, but this figure is likely to increase
as indicated by the large number of undescribed taxa that have been detected
in recent years. The Hybosoridae is a heterogeneous group of relatively small
scarabs, with adults usually ranging in size from 3-7 mm. The majority of
the species are brown or black. The antennae are 9-10 segmented, with a 3-segmented
club. Little is known about the biology of hybosorid species. While these
are useful to diagnose most species of the Hybosoridae, many exceptions are
found.
Description
Length 5.0-7.0 mm. Shape oval, dorsal surface convex. Color light brown to
black, shining. Head not deflexed. Antennae 10-segmented with 3-segmented,
opposable club (last 2 segments tomentose), first segment of club hollowed
to receive segments 2 and 3, basal segment of antenna expanded apically. Eyes
with eucone ommatidia, divided by reduced canthus. Clypeus lacking tubercle
or horn. Labrum truncate, produced beyond apex of clypeus, prominent. Mandibles
produced beyond apex of labrum, prominent, external edge rounded, apex pointed.
Maxillae with 4-segmented palpi; labium with 4-segmented palpi. Pronotum convex,
base wider than elytral base. Elytra convex, surface polished, glabrous. Pygidium
concealed by elytra. Scutellum exposed, triangular. Legs with anterior coxae
conical, contiguous; mesocoxae contiguous; protibiae tridentate on outer margin,
apex with one spur; meso- and metatibia with prominent, oblique ridge, apex
with 2 spurs; spurs mesad, adjacent (not separated by basal metatarsal segment);
tarsi 5-5-5; claws equal in size, simple; empodium short, not extending beyond
fifth tarsal segment, with 2 setae. Abdomen with 6 free sternites (first sternite
obscured by hind coxae except at lateral edges); 8 functional abdominal spiracles,
situated in pleural membrane (spiracles 1-7) and in tergite (spiracle 8).
Wings well developed, with 2 apical detached veins. Male genitalia variable.
References: Cooper 1983, Scholtz 1990.
Classification Status
The Hybosoridae is considered as a family within the Scarabaeoidea or as a
subfamily of the family Scarabaeidae. In this volume, we follow Gardner (1935),
Paulian (1939), and Lawrence and Newton (1995) and consider the group a family.
Hybosorid larvae are distinct and are the primary reason that the group is
treated as a family. Larvae possess prothoracic and mesothoracic stridulatory
structures and three truncate lobes at the apex of the labrum, both of which
are unique to this group. In adults, the form of the antenna (10-segmented
with a 3-segmented club, the first segment hollowed to receive segments two
and three) is unique. The Hybosoridae is hypothesized to be intermediate between
the Ochodaeidae and Ceratocanthidae (Scholtz et al. 1988) or intermediate
between the Trogidae and Ceratocanthidae (Howden and Gill 1988). Aside from
revisions of some genera and catalogs, little systematics work has been conducted
on this group.
Distribution
The Hybosoridae contains 29 genera world-wide and about 200 species (Allsopp
1984; Martinez 1994). Species are widely distributed in the tropics. Fifteen
genera and about 65 species occur in the New World. Phaeochrous emarginatus
Laporte, a species that occurs in Africa, Australia, and India, was once reported
from California, but the species is not established in California and the
record was probably in error (Evans, pers. comm. 1998).
Subfamilies of Hybosoridae
Anaidinae
Ceratocanthinae
Hybosorinae
Liparochrinae
Pachyplectrinae
Ecology
Little is known about the biology of hybosorid species. Adults feed on dung,
carrion, fungi, or rotting wood, and some are found in ant and termite nests.
Some species, particularly in the Australian genus Liparochrous Erichson and
those of the subfamily Ceratocanthidae, are capable of rolling up their body
to form a compact ball. Larvae are known for only six species in five genera,
and they were collected in decomposed plant material or under bark. Larvae
and adults of some species are known to stridulate.
Larvae
Form scarabaeoiform (C-shaped, cylindrical). Color creamy-white or yellow
(except at caudal end which may be darkened by accumulated feces). Cranium
heavily sclerotized, brown to dark brown. Antennae 3 or 4-segmented (if 3-segmented,
then third and fourth segments fused). Frontoclypeal suture distinct. Labrum
at apex with 3 truncate lobes. Epipharynx with row of setae on each chaetoparia,
a blunt tooth in the haptomeral region, and united tormae. Maxilla with galea
and lacinia distinctly separate; maxillary stridulatory area consisting of
a row of conical teeth; maxillary palp 3- or 4-segmented. Abdominal segments
1-6 with 3 annuli, each with 1 or more transverse rows of short setae. Spiracles
cribriform, with closing apparatus. Venter of last abdominal segment with
raster consisting of 2 curved rows of many short setae that converge caudally.
Legs 4-segmented, well developed, with stridulatory apparatus on pro- and
mesothoracic legs, each with a well-developed claw. References: Ritcher 1966;
Scholtz 1990.
References Cited
ALLSOPP, P. G. 1984. Checklist of the Hybosorinae (Coleoptera:
Scarabaeidae). Coleopterists Bulletin 38: 105-117.
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. 1,121
pp.
GARDNER, J. C. M. 1935. Immature stages of Indian Coleoptera (16)
(Scarabaeidea). Indian Forest Rec. (New Series) Ent. 1:1-33.
HOWDEN, H. F. and B. D. GILL. 1988. A fourth genus of unusually modified
Ceratocanthinae (Coleoptera: Scarabaeidae) from South Africa. Canadian Journal
of Zoology 66: 2077-2079.
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.
MARTINEZ, A. 1994. Notas sobre Hybosorinae (Coleoptera: Scarabaeidae),
II. Elytron 8: 223-239.
PAULIAN, R. 1939. Les caractères larvaires des Geotrupidae
(Col.) et leur importance pour la position systématique du groupe.
Bulletin de la Société Zoologique de France 64: 351-360.
RITCHER, P. O. 1966. White Grubs and Their Allies: A Study of North
American Scarabaeioid Larvae. Oregon State University Press, Corvallis. 219
pp.
SCHOLTZ, C. H. 1990. Phylogenetic trends in the Scarabaeoidea
(Coleoptera). Journal of Natural History 24: 1027-1066.
SCHOLTZ, C. H., D. D'HOTMAN, A. V. EVANS, and A. NEL. 1988. Phylogeny
and systematics of the Ochodaeidae (Insecta: Coleoptera: Scarabaeidae). Journal
of the Entomological Society of South Africa 51: 207-240.