Glaresis

Introduction

Glaresidae is a small family of scarabaeoid beetles of about 50 species. This family occurs throughout the world, except in Australia, usually in sandy regions, such as the Sonoran Desert in the southwest United States and the Kalahari Desert in Namibia, South Africa and Botswana.

Glaresidae adults are commonly collected using blacklights and when they do occur, usually are attracted in large numbers. Adults are typically very small, about 2-5 mm long, oblong, convex and reddish-brown to light brown. The larvae and habits are unknown. Some glaresid researchers suspect that both adults and larvae may live in association with ants or termites where they feed on subterranean fungi.

Since glaresids display a plethora of primitive characteristics, but very few novel ones, they are thought to be very close in structure to the ancestor of the Scarabaeoidea. This makes them very important to students of the Scarabaeoidea in that they provide a basis of comparison when evaluating relationships between other members of the superfamily.

Characteristics

Perhaps the most well-known attribute of adult glaresids is their virtual lack of derived structures although they do posses numerous characteristic, but primitive, features.

Adults are characterized by: 10-jointed antennae with a 3-jointed club; eye with a canthus, and with eucone ommatidia; epipharynx with single tormae and lateral combs not in rows; mandibles toothed, with a prostheca and distinct molar area; maxilla with lobed galea and lacinia terminating in two teeth, palpi 4-jointed; labium consists of fused mentum and prementum, and a triangular, partly bilobed ligula; tentorium with single-foramen and small anterior and median bridges; protrochantin concealed; procoxal cavities closed; mesocoxal cavities open; generalized mesothoracic spiracles and intersegmentalia; wings with radial cell eyelet-like, distally strengthened; central folding field triangular; RP1 reduced; RP3+4 completely reduced; medial spur reaches the posterior margin; AA1+2 spike-like but recovers its course and reaches the posterior margin; JA and JP partially reduced; 1Ax broad, ventral projection and FSc1 very short and narrow, distal embayment weakly concave, and PRR articulation very weak; 2Ax proximal lobe very small, strongly depressed below the ridge, distal lobe very large and harp-shaped, anterior section of the dorso-proximal ridge absent, dorso-distal ridge weakly elevated, feebly distinct and the anterior section very short, medial groove very weak anteriorly, FR strikingly broadly ovoid and large, and very broadly articulated with the distal ridge and lobe; median plate broadly articulated with 1-3Ax, FM1 and FM2 separated by membrane and FM2 small; 3Ax head dorsally very broad and moderately convex, anterior margin convex, FCu very large, posterior section of the neck ridge absent, AXCu present as a very slender anteriad extension along the proximal margin of head, tail very narrow and convex, window or medial weakening absent, and suture line between AXA, AXJ and FJ present; 1BP with HP very weakly curved postero-dorsad, BScA moderately large and oriented antero-distad, ScA large and broad, separated from BScA by a deep concavity, BR broadly open, long, partially depressed below BScA, with a very small proximal arch, an indistinct br and distal arch absent; 2BP large, broad, moderately sclerotized with BMA distinct, strongly convex, partially anterior to BMP, BMA and BMP completely fused posteriorly and incompletely so anteriorly, BMP flattened and strongly depressed below BMA, BMP-BCuA brace slender, moderately sclerotized and MA weak but present; tarsal empodium absent; 5 visible abdominal ventrites; abdominal spiracles situated in pleural membrane, all functional; male genitalia a simple symmetrical trilobe; genital capsule distinct; four or six ovarioles present per ovary; karyotype 9+Xyp (Scholtz et al. 1994).

Out of all the characters studies, only two autapomorphic states, those of reduced RP1 and RP3+4 vein branches, could be unequivocally assigned to the Glaresidae (Scholtz et al. 1994).

Only two characters are unequivocally more primitive in groups other than Glaresidae, the exposed protrochantin and the open procoxal cavities. However, the two families that have one (Diphyllostomatidae) or both (Pleocomidae) primitive states have numerous characters in more derived states which they share with other scarabaeoid groups than do Glaresidae. Consequently, Glaresidae are the most primitive living scarabaeoids and represent the sister group of the rest of Scarabaeoidea. It is the current belief that Glaresidae are probably very similar in structure to the ancestral scarabaeoid (Scholtz et al. 1994).

Relationships of Glaresids to other Scarabaeoids

Glaresis has traditionally been considered a member of the Trogidae by most authors. Although this system was followed by students of the Scarabaeoidea it was usually with misgiving, and doubts about the placement of Glaresis in the Trogidae were expressed verbally by Crowson, Howden and Paulian (Scholtz 1986). It was removed from the Trogidae by Scholtz (1986) after phylogenetic analysis of the elements of the Trogidae, but he offered no substantiated alternative to its placement in the Scarabaeoidea. Scholtz et al. (1987) reassessed the position of Glaresis and concluded that it is not clearly related to any other scarabaeoid group, and that it is primitive and lies close to the basic evolutionary stock from which the Scarabaeoidea evolved. Because Glaresis shows no affinities to any other group, they erected a family to accommodate it (Scholtz et al. 1994).

Since the study by Scholtz et al. (1987) a large body of morphological evidence accumulated supporting the assumption that the Glaresidae are the most primitive living scarabaeoids. The morphological evidence was presented by Browne (1993) and Scholtz et al. (1994). Subsequent comprehensive cladistic analyses confirming the view that Glaresidae is the most primitive living scrabaeoid are presented by Browne (1993, wing characters only), Browne & Scholtz (1995, wing characters only) and Browne & Scholtz (in preparation, all available morphological, biological and genetic characters). This view has gained widespread acceptance.

Other Names for Glaresis

• Glaresidae
• Enigmatic scarab beetles

References

Browne, D.J. 1993. Phylogenetic significance of the hind wing basal articulation of the Scarabaeoidea (Coleoptera). Ph.D. thesis, University of Pretoria.

Browne, D.J. and C.H. Scholtz. 1995. Phylogeny of the families of Scarabaeoidea (Coleoptera) based on characters of the hindwing articulation, hindwing base and wing venation. Systematic Entomology 20(3):

Jameson, M. L. 2002. Glaresidae. pp. 15-16 in Arnett, R.H., Jr., M. C. Thomas, P. E. Skelley and J. H. Frank. (eds.). American Beetles. Volume 2. Polyphaga: Scarabaeoidea through Curculionoidea. CRC Press LLC, Boca Raton, FL. xiv + 861 pp.

Scholtz, C.H. 1986. Phylogeny and systematics of the Trogidae (Coleoptera: Scarabaeoidea). Systematic Entomology 11: 355-363.

Scholtz, C.H., D.J. Browne and J. Kukalová-Peck. 1994. Glaresidae, archaeopteryx of the Scarabaeoidea (Coleoptera). Systematic Entomology 19: 259-277.

Scholtz, C.H., D. D'Hotman and A. Nel. 1987. Glaresidae, a new family of Scarabaeoidea (Coleoptera) to accommodate the genus Glaresis Erichson. Systematic Entomology 12(3): 345-354.

Scholtz, C.H., D. D'Hotman, A.V. Evans and A. Nel. 1988. Phylogeny and systematics of the Ochodaeidae (Coleoptera: Scarabaeoidea). Journal of the Entomological Society of Southern Africa 51: 207-240.