The Bess Beetle family is most diverse in tropical regions. Members of this family are typically large beetles (20 to 70 mm long) with a sublamellate antennal club. The form of body (elongate and dorsoventrally depressed) and form of the mentum (deeply emarginate apically) help to distinguish this family from other scarabaeoids. Adults and larvae live together in subsocial groups in rotting logs.

Length 15.0-70.0 mm. Shape elongate-cylindrical and depressed. Color black (tenerals orange to deep maroon); ventral surface with or without erect, moderately dense, yellow setae. Head prognathus, narrower than thorax, often with dorsomedian horn. Antennae 10-segmented, with 3-segmented club that is not opposable and not geniculate (but is capable of being rolled together); segments of club tomentose; antennae inserted under a prominent frontal margin. Eyes divided in half by canthus, with exocone ommatidium. Clypeus reduced, separated from frons by suture, or vertical and hidden beneath frons. Labrum distinct, prominent, projecting beyond apex of front of head, clypeal apex deeply emarginate, bisinuate, or truncate. Mandibles projecting beyond apex of labrum, large, curved, toothed, blunt. Maxillae with 4-segmented palpi; galea with apical hook; submentum large, prominent; mentum large, emarginate at apex; labium with 3-segmented palpi. Pronotum broader than head, quadrate, surface smooth with median, longitudinal groove. Elytra elongate, sides parallel, apices rounded, with striae well developed. Pygidium concealed by elytra. Scutellum triangular, small (exposed only in groove between pronotum and elytra). Legs with transverse coxae, mesocoxae closed; protibiae with several external teeth on outer margin, apex with 1 spur; meso- and metatibiae with ridges, apices with 2 spurs; spurs mesad, adjacent (not separated by basal metatarsal segment); tarsal formula 5-5-5; claws equal in size, simple; empodium present, not extending beyond fifth tarsal segment, with 2 setae. Abdomen with 5 visible sternites; 7 functional abdominal spiracles situated in pleural membrane. Wings well developed without M-Cu loop, with 1 apical detached vein. Male genitalia trilobed. Female genitalia with paraprocts, proctiger, and styli absent; valvifers and coxite present. References: Scholtz 1990; Sharp and Muir 1912; Tanner 1927.

Classification Status

Taxonomy of the species in the United States, Mexico and Central America is well known, although new species are still being found. Taxonomy of passalids in other regions of the world needs further study. Monophyly of the family is supported by larval and adult characteristics (see Scholtz 1990; Browne and Scholtz 1995). According to the phylogenetic analysis of Browne (1993), the Passalidae is the basal member of a clade that includes the Diphyllostomatidae, Lucanidae, Glaphyridae, Trogidae, Bolboceratinae (Geotrupidae), and Pleocomidae. World catalog: Hincks and Dibb 1935. Keys to Nearctic genera: Reyes-Castillo 1970; Schuster 1983a. Keys to genera of larvae: Schuster 1992.

There are over 500 described species, nearly all of which are tropical. A fossil passalid beetle, Passalus indormitus Cockerell, is known from Oligocene deposits of Oregon (Reyes-Castillo 1977). It is very similar to P. punctiger.

Passalid adults live in well decayed logs and stumps with their larvae and subsocial family groups. All stages are found in galleries in wood that are excavated by the adults. Eggs are usually placed together in a "nest" of frass. In many species, recently oviposited eggs are red; as they mature, they change to brown, then to green. Adults and larvae communicate by stridulating and can produce 14 different calls. Adults care for larvae and prepare food by chewing it and presumably mixing it with saliva. Both adults and larvae need to feed on adult feces that are predigested by microflora (essentially an external rumen). Biology: Reyes-Castillo 1970; Reyes-Castillo and Halffter 1984; Schuster 1975a, 1975b, 1983b; Gray 1946; Schuster and Schuster 1997; Ratcliffe 1991.

Form elongate, subcylindrical, slightly curved (not c-shaped). Color creamy white or blue-white (except at caudal end which may be darkened by accumulated feces). Cranium lightly sclerotized. Antennae 2-segmented with protruding fleshy base, short. Lateral ocelli lacking. Frontoclypeal suture distinct. Labrum rounded, setiferous at apex; maxilla with galea and lacinia distinctly separate, stridulatory area present, palpi 2-segmented (apparently 3-segmented). Abdominal segments without annuli. Spiracles cribriform with C-shaped peritremes. Venter of last abdominal segment with 2 anal lobes. Pro- and mesothoracic legs 4-segmented, with long, curved claw; metathoracic leg unsegmented, reduced to a stub with several apical teeth that rub against stridulatory area on coxa of mesothoracic leg. References: Böving and Craighead 1930-1931; Krause and Ryan 1953; Ritcher 1966; Scholtz 1990. Keys to larvae: Schuster 1992; Schuster and Reyes-Castillo 1981.

References Cited
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.

BROWNE, D. J. and C. H. SCHOLTZ. 1995. Phylogeny of the families of the Scarabaeiodea (Coleoptera) based on characters of the hindwing articulation, hindwing base and wing venation. Systematic Entomology 21: 145-173.

BOVING, A. G. and F. C. CRAIGHEAD. 1930-1931. An illustrated synopsis of the principal larval forms of the Coleoptera. Reprint edition, Brooklyn Entomological Society, Merrick, NY. 351 pp.

GRAY, I. E. 1946. Observations on the life history of the horned Passalus. American Midlands Naturalist 35: 728-746.

HINCKS, W. D. and J. R. DIBB. 1935. Passalidae, Coleopterorum Catalogus pars 142: 1-118.

KRAUSE, J. B. and M. T. RYAN. 1953. Annals of the Entomological Society of America. 47: 1-20, 4 pls.

RATCLIFFE, B. C. 1991. The Lucanidae and Passalidae (Insecta: Coleoptera) of Nebraska. Great Plains Research 1: 249-282.

REYES-CASTILLO, P. 1970. Coleoptera: Passalidae; morfologia y division en grandes grupos; generos americanos. Folia Entomologica Mexicana 20-22: 1-240.

REYES-CASTILLO, P. 1977. Systematic interpretation of the Oligocene fossil Passalus indormitus (Coleoptera: Passalidae). Annals of the Entomological Society of America 70: 652-654.

REYES-CASTILLO, P. and G. HALFFTER. 1984. La estructura social de los Passalidae (Coleoptera: Lamellicornia). Folia Entomologica Mexicana 61: 49-72.

RITCHER, P. O. 1966. White Grubs and their Allies. Oregon State University Press, Corvallis, OR.

SCHOLTZ, C. H. 1990. Phylogenetic trends in the Scarabaeoidea (Coleoptera). Journal of Natural History 24: 1027-1066.

SCHUSTER, J. C. 1975a. A comparative study of copulation in Passalidae (Coleoptera): New positions for beetles. Coleopterists Bulletin 29: 75-81.

SCHUSTER, J. C. 1975b. Comparative behavior, acoustical signals and ecology of New World Passalidae (Coleoptera). Ph.D. Thesis. University of Florida. 127 pp.

SCHUSTER, J. C. 1983a. The Passalidae of the United States. Coleopterists Bulletin 37: 302-305.

SCHUSTER, J. C. 1983b. Acoustical signals of passalid beetles: complex repertoires. Florida Entomologist 66: 486-496.

SCHUSTER, J. C. 1992. Passalidae: state of larval taxonomy with description of New World species. Florida Entomologist 75: 358-369.

New World genera of Passalidae (Coleoptera): a revision of larvae. Anales de la Escuela Nacional de Ciencias Biologicas, Mexico 25: 79-116.

SCHUSTER, J. C., and L. B. SCHUSTER. 1997. The evolution of social behavior in Passalidae, 260-269 p. In Choe, J. and Crespi, B. (eds.), The Evolution of Social Behavior in Insects and Arachnids. Cambridge University Press, Cambridge.

SHARP, D. and F. MUIR, F. 1912. The comparative anatomy of the male genital tube in Coleoptera. Transactions of the Entomological Society of London 1912: 477-642.

TANNER, V. M. 1927.
The female genitalia of Coleoptera. Transactions of the American Entomological Society 53: 3-50.