Horned Scarabs

Scarabaeidae, Dynastinae. Spanish: Cucarrones (Colombia).

Horned scarabs may weigh up to 40 grams and be as bulky as a human fist. Including the anteriorly projecting horns, many attain body lengths of 12 to 13 centimeters. In these, the development of the horns varies much through disproportionate (allometric) growth, although they tend to sort into two extreme size categories (Eber-hard 1987). Smaller individuals normally have very poorly formed horns; the larger individuals have tremendously elongated projections; a few fall in between. These are classed as minors, mediums, and majors, like the classes of ant workers based on overall body size and relative size of the jaws (Eberhard 1982).

Such appendages are known to be an outcome of sexual selection, for females usually lack them almost completely. Horns for grasping and prying, largeness, and great strength favor the males, who employ these attributes in combat for territory and mating rights, although minor males ("satellite males," see centris bees) may use their quickness and relative inconspicuousness to sneak by larger rivals preoccupied with fighting and successfully mate (Eberhard 1980, 1982).

The taxonomy of this major group has been reviewed by Endródi (1966, 1984).

References

Eberhard, W. G. 1980. Horned beetles. Sci.

Amer. 242(3): 166-182. Eberhard, W. G. 1982. Beetle horn dimorphism: Making the best of a bad lot. Amer. Nat. 119: 420-426. Eberhard, W. G. 1987. Use of horns in fights by the dimorphic males of Aegopsis nigricollis (Coleóptera, Scarabaeidae, Dynastinae). Kans. Entomol. Soc. J. 60: 504-509. Endródi, S. 1966. Monographic der Dynastinae (Coleóptera, Lamellicornia). I. Teil. Staat. Mus. Tierkunde Dresden Entomol. Abhand. 33: 1-457.

Endródi, S. 1984. The Dynastinae of the world. Junk (Ser. Entomol. 28), The Hague.

Hercules Beetles

Scarabaeidae, Dynastinae, Dynastini, Dynastes. Spanish: Tijeras (General). French: Scieurs de long (Guadeloupe).

Males of the large beetles in this genus are easily recognized by their very long, down-curved medial prothoracic horn whose length, plus that of the body, makes them some of the largest beetles in the world. Specimens as long as 17 centimeters are known. Without the horn, the body length is considerably less, to 8 centimeters, but still great enough to rival the rhinoceros beetles for the record. Their live weight may approach 40 grams. Females lack horns of any size (fig. 9.7b), but their bodies are nearly as massive as those of the males (BL to 8 cm).

The strength of the larger species is also prodigious. Males are capable of exerting tremendous force in the closure of the prothoracic horn against the horn of the head. In one experiment, a live beetle was observed to lift a 2-kilogram weight with its head horns, exerting a force of 140 New-tons (or 1.4 X 107 dynes) (Jarman and Hinton 1974). A male I once kept in a bird cage demonstrated its power by escaping at will, simply by bending the heavy metal wires apart with the force of its body.

The elytra of the best-known species, D. hercules (fig. 9.7a, b), are usually olive-yellow, although this color may change to black and back again within a few minutes. It is not clear how much control the beetle (usually males) has over this change; it seems to be a function more of ambient humidity. A spongy yellow layer beneath the outer cuticle layer when saturated allows the black underlayers to show; when dry, the layer reflects yellow (Hinton and Jarman 1973).

The horns of the males are definitely used as grappling devices in combat over females, who may be carried off by the victor. (See horned beetles, above). William Beebe (1947) describes such beetles eloquently.

Males also stridulate when stimulated, during combat or artificially, making a soft "zizzing squeak" or "huff." The abdomen is moved so that a roughened area on either side of the enlarged last segment is rubbed against the inner apices of the elytra (Jarman and Hinton 1974).

These are essentially forest dwellers. Adults are attracted to sap oozing from wounded trees (especially palms) and by sweet fruits. They are nocturnal and arrive at electric lights around which their loud and powerful flight can be appreciated.

Figure 9.7 HORNED SCARAB BEETLES (SCARABAEIDAE). (a) Hercules beetle (Dynastes hercules), male, (b) Hercules beetle, female, (c) Rhinoceros beetle (Megasoma sp.), larva, (d) Elephant beetle (Megasoma elephas), male.

Females oviposit in crevices in the bark of hosts, which are Licania ternatensis (Rosa-ceae), Amanoa caribaea (Euphorbiaceae), Inga (Fabaceae), and other trees (Verrill 1907, Gruner and Chalumeau 1977).

Legend has it in Guadeloupe that D. hércules can cut a tree limb by grasping it with the horns and flying around and around until it is severed or sap is caused to flow, on which it then feeds (Gruner and Chalumeau 1977). (See long-horned beetles, below.) In some regions, the mythical aphrodisiacal powers of ground rhinoceros horn are attributed to the horns of these beetles as well (orig. obs.).

There are four species of Dynastes in the Neotropics (hercules, neptunus, satanas and kyllus) (Dechambre 1980). The prothorax of the first three is black; that of hyllus is gray green. Only D. hercules has normal terminal tarsal segments in the legs. In D. neptunus and D. satanas the last tarsal segments are dilated, but in the former the accessory prothoracic horns originate well below the base of the main horn; in satanas, these horns arise on the same level as the major horn.

Dynastes hercules and D. neptunus are widespread throughout Middle America, including the northern half of South America; D. satanas is Bolivian only; and the relatively small, slightly horned D. hyllus is from Central Mexico (Dechambre 1980, Morón 1987).

D. hercules on the island of Guadeloupe harbors a mite parasite (Costa 1976).

References

Beebe, W. 1947. Notes on the Hercules beetle, Dynastes hercules (Linn.), at Rancho Grando, Venezuela, with special reference to combat behavior. Zoologica 32: 109-116.

Costa, M. 1976. Dynastaspis hercules sp. n., a new gamasine mite associated with the Hercules beetle in Guadeloupe. Acarologia 18: 187-193.

Dechambre, R.-R 1980. Le genre Dynastes (Coleoptera Scarabaeoidea Dynastidae). Soc. Sci. Nat. (France) Bull. 28: 5-10.

Gruner, L., and F. Chalumeau. 1977. Biologie et élevage de Dynastes h. hercules en Guadeloupe (Coleoptera, Dynastinae). Soc. Ento-mol. France Ann. (n.s.)13: 613-624.

Hinton, H. E., and G. M. Jarman. 1973. Physiological colour change in the elytra of the Hercules beetle, Dynastes hercules. J. Ins. Physiol. 19: 533-549.

Jarman, G. M., and H. E. Hinton. 1974. Some defense mechanisms of the Hercules beetle, Dynastes hercules. J. Entomol. (Ser. A) 49: 71 — 80.

Morón, M. A. 1987. Los estados inmaduros de Dynastes hyllus Chevrolat (Coleoptera: Melo-lonthidae: Dynastinae): Con observaciones sobre su biología y el crecimiento alométrico del imago. Fol. Entomol. Mexicana 72: 33— 74.

Verrill, A. H. 1907. Description of a new species or sub-species of Flercules beetles from Dominica Island, B.W.I., with notes on the habits and larvae of the common species and other beetles. Amer. J. Sci. (Ser. 4) 24: 305-308.

Rhinoceros Beetles

Scarabaeidae, Dynastinae, Dynastini,

Megasoma. Spanish: Papasos (Peru), cornizuelos (Costa Rica), congarochos

(Venezuela), bobutes (Andes).

From the standpoint of bulk, males of certain species of these beetles are the biggest insects in the world. Large living specimens of M. actaeon may weigh 30 grams. From head to the apex of the abdomen, someM. elephas individuals measure up to 8 centimeters; including the head horn, they attain lengths of 13 centimeters or more and can weigh 35 grams. Curiously, these beetles behave much like small mammals in their ability to metaboli-cally increase their body temperature when the air cools (Morgan and Bartholomew 1982).

Their common name refers to the long, slender, upcurved, rhinoceroslike head horn of the males. The apical bifurcation of the horn distinguishes them from other very large regional horned scarabs in which this armament always has a simple apex or is down curved. The prothoracic shield may also bear a central horn and triangular lateral horns. Females lack horns altogether.

There are seven species in the genus, found in undisturbed lowland forest throughout the tropical and subtropical regions of Latin America (Hardy 1972). Males of the three best known are easily separated: the elephant beetle, M. elephas (fig. 9.7d), has a velvety brown, textured integument; M. actaeon is dull black with forward-pointing thoracic horns; M. mars is shiny black with divergent thoracic horns.

The larvae of these monstrous beetles also are insect behemoths themselves. They are typical curved scarab grubs but when mature may reach lengths to 13 centimeters with the body extended (fig. 9.7c). Some attack small living palms, but most feed in the pulp of dead palm trunks

(Cocos, Mauritia, etc.) and probably take three to four years to mature. Because Ai. elephas occidentalis is considered a pest of young Licistona chinensis (Reitter 1961: 42), it has been studied in some detail (Morón 1977).

Adults may be discovered on palm inflorescences and fruit; they also come to artificial lights during their nocturnal flights. In northern Brazil and other parts of Amazonia, various tribes make amulets or fetishes from parts of Megasoma. The horns symbolize sexual and physical power and are believed to increase potency and protect one from disease. Like those of the rhinoceros and hercules beetles, the head horns are ground and taken by some unenlightened people in the hope of improving their sexual powers. The horns are useful, in fact, only to the beetles as fighting instruments. Males engage in combat for rights to a female or feeding site (Beebe 1944) in a manner similar to Hercules beetles.

References

Beebe, W. 1944. The function of secondary sexual characters in two species of Dynastidae (Coleoptera). Zoologica 29: 53-58, Pis. 1-V. Hardy, A. R. 1972. A brief revision of the North and Central American species of Megasoma (Coleoptera: Scarabaeidae). Can. Entomol. 104: 765-777. Morgan, K. R., and G. A. Bartholomew. 1982. Homeothermic response to reduced ambient temperature in a scarab beetle. Science 216: 1409-1410. Morón, M. A. 1977. Description of the third-stage larva of Megasoma elephas occidentalis Bolívar y Pieltain et al. (Scarabaeidae: Dynastinae). Coleop. Bull. 31: 339-345. Reitter, E. 1961. Beetles. Putnam's Sons, New York.

Golofas

Scarabaeidae, Dynastinae, Oryctini, Golofa. Spanish: Torneadores (General), toritos (Peru), aserradores (Venezuela).

This is a fairly large genus (Dechambre 1979, Voirin 1979) of moderate to large (BL

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