Scarab beetles comprise a speciose group, and they are a conspicuous component of the beetle fauna in the New World. Adults of many scarab beetles are noticeable due to their relatively large size, bright colors, often elaborate ornamentation, and interesting life histories. The family includes the Goliath beetle from Africa (Goliathus goliathus L.), known as one of heaviest insects (up to 100 grams). It also includes the elephant beetle (Megasoma elephas L.) and hercules beetle (Dynastes hercules Fabr.), both from the American tropics, that are known for their large size (up to 160 mm for the hercules beetle) and highly developed horns in the males. The group includes over 27,800 species worldwide, an intriguing array of life histories, and many interesting adaptations.
Length 2.0-180.0 mm. Shape variable; ovate, obovate, quadrate, cylindrical. Color variable, with or without metallic reflections or metallic coloration; with or without vestiture. Head weakly deflexed or not deflexed. Antennae 10-segmented (rarely 9-segmented) with 3 to 7-segmented, opposable club; club with apical segments nearly glabrous [Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae, Valginae] or with all segments tomentose [Aphodiinae, Scarabaeinae]. Eyes with eucone ommatidia, partially divided by a canthus. Clypeus with or without tubercle or horn. Labrum usually distinct, produced or not beyond apex of clypeus. Mandibles variable, produced or not beyond apex of labrum. Maxillae with 4-segmented palpi. Labium with 3-segmented palpi. Pronotum variable, with or without horns or tubercles. Elytra convex or flattened, with or without striae. Pygidium concealed by elytra [Aphodiinae, Scarabaeinae] or exposed [Scarabaeinae, Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae, Valginae]. Scutellum exposed or not; shape triangular or parabolic. Legs with coxae transverse or conical; protibiae tridentate, bidentate, or serrate on outer margin, apex with one spur; meso- and metatibia slender or robust, apex with 1 or 2 spurs; spurs mesad, adjacent or separated by basal metatarsal segment; tarsi 5-5-5, anterior tarsi absent in some Scarabaeinae; claws variable, equal in size or not, simple or toothed; empodium present, extending beyond fifth tarsal segment, with 2-5 setae or with setae absent. Abdomen with 6 free sternites; 7 functional abdominal spiracles situated in pleural membrane [Aphodiinae, Scarabaeinae] or in pleural membrane, in sternites, and in tergite [Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae, Valginae]. Wings well developed, M-Cu loop and 1 apical, detached vein present. Male genitalia variable, bilobed, or fused. References: Cooper 1983; Scholtz 1990.
The past thirty years have seen many changes and debates in the classification of the Scarabaeidae. In the "traditional" North American system, the Scarabaeidae has been treated as including the all scarabaeoid families except the Passalidae and Lucanidae. Old World scarab workers have tended to split the Scarabaeidae into several families. While the debate continues, we follow Lawrence and Newton (1995) and consider the family Scarabaeidae to include the subfamilies Aclopinae, Aphodiinae, Scarabaeinae, Melolonthinae, Dynastinae, Orphninae, Allidiostomatinae, Rutelinae, Cetoniinae, Trichiinae, and Valginae. No phylogenetic analyses have addressed the relationships of all of these taxa. However, most hypotheses generally consider the Aphodiinae and Scarabaeinae as the sister group to the Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae, and Valginae.
The family Scarabaeidae is sometimes referred to as the family Melolonthidae, especially by some Latin American workers. In this usage, the family is comprised of the subfamilies Melolonthinae, Euchirinae, Phaenomeriidnae, Dynastinae, Cetoniinae, Glaphyrinae, and Systellopodinae (Endrödi, 1966) while the Scarabaeidae refers to everything else except the Passalidae, Lucanidae, and Trogidae. This system is not in wide use today.
Taxonomy of the world Scarabaeidae is variably known. The taxonomy of the world Dynastinae is fairly well established due to the work of Endrödi (1985). Most Melolonthinae, Rutelinae, and Cetoniinae are so poorly known taxonomically that many New World genera cannot be reliably identified. Taxonomy of the Scarabaeinae (Hanski and Cambefort 1991) and Aphodiinae is fairly well established (Dellacasa 1987, 1988a, 1988b, 1991, 1995).
The family Scarabaeidae includes about 91% of all scarabaeoids and includes about 27,800 species worldwide. Within the Scarabaeidae, the Aphodiinae and Scarabaeinae include approximately 6,850 species worldwide (about 22% of scarabaeoids and 25% of Scarabaeidae). The subfamilies Orphninae, Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae and Valginae include approximately 20,950 species (about 69% of scarabaeoids and 75% of Scarabaeidae). About 600 genera scarab beetles occur worldwide.
New World Subfamilies and Tribes
Life histories of scarab beetles are incredibly diverse and include adults that feed on dung, carrion, fungi, vegetation, pollen, fruits, compost, or roots. Some scarab beetles live in the nests of ants (myrmecophiles), in the nests of termites (termitophiles), or in the nests of rodents or birds. Some species of dung beetles (Scarabaeinae) care for their larvae or the larval brood ball (e.g., species of Canthon and Copris). Adults of some scarab beetles are diurnal and can be observed on flowers or vegetation (e.g., Euphoria, Cotinis [Cetoniinae]) while many species are nocturnal are attracted to lights at night (e.g., Dynastes [Dynastinae], Plusiotis [Rutelinae], Polyphylla [Melolonthinae]). Adults and larvae of a few species of scarabs are economically important and may cause considerable damage due to defoliation or root-feeding (e.g., Popillia japonica Newman [Rutelinae]). Many scarabs are beneficial because they pollinate plants, recycle plant material, and are valuable dung recyclers. In 1968, for example, several species of dung beetles were introduced to Australia to control cattle feces. Domesticated cattle produce feces dissimilar from native Australian herbivores. Native Australian dung beetles were not adapted to feed on the dung of domesticated cattle. As a result, cattle feces accumulated at such a rate that grasses and forbes were smothered and killed. Dung beetles were introduced from Africa, and these beetles readily fed on cattle dung, enriched the soil with the dung, and allowed the grasses and forbes to thrive. The dung beetles also eliminated breeding sites for pestiferous, dung-breeding flies.
"Dung beetle" is a common name applied to beetles in the subfamilies Scarabaeinae and Aphodiinae. Species in these groups often have specific ecological requirements. For example, Dialytes spp. and Aphotaenius carolinus (Van Dyke) (both Aphodiinae) are specialists on deer dung. Some dung beetles, the so-called "tumble bugs" (e.g., Canthon pilularius (L.) [Scarabaeinae]), form a ball of dung and roll it away from potential competition at a dung pat. Other dung beetles make a ball of dung under the dung pile (e.g., Copris fricator (Fabr.), Phanaeus vindex (MacLeay), Onthophagus hecate (Panzer), Onthophagus cribricollis Horn [all Scarabaeinae]). Scarab beetles that live in the nests of vertebrates include: Onthophagus polyphemi Hubbard (Scarabaeinae) that lives in the nest of gophers in Florida; Ataenius brevinotus Chapin (Aphodiinae) that lives in the nest of fox squirrels in Florida, and; many species of Aphodius (Aphodiinae) that live in the nests of prairie dogs and pocket gophers. Although most dung beetles feed on dung, some, such as Onthophagus striatulus (Beauvois) [Scarabaeinae], defy their common name and feed on fungi.
Some scarabs, such as Euparia castanea Serville (Aphodiinae) and Cremastocheilus spp. (Cetoniinae) are inquilines in the nests of ants. Species in the genus Valgus (Valginae) are inquilines in the nests of termites. The life history of these beetles, their adaptations, and their body form is intimately intertwined with their hosts.
Most species in the subfamilies Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, and Trichiinae feed on plant products. Larvae of many dynastines and rutelines feed on rotting wood. Larvae of many melolonthines (e.g., Phyllophaga species), rutelines (e.g., Anomala species), and dynastines (e.g., Cyclocephala species) feed on grass roots. Some of these larvae may be lawn pests (e.g., Popillia japonica Newman [Rutelinae], Cyclocephala borealis Arrow [Dynastinae], Amphimallon majalis Razoumowski, Plectris aliena Chapin, and Phyllophaga species [all Melolonthinae]). As adults, most species in these subfamilies feed on leaves or fruits. Adults of Listrochelus falsus LeConte (Melolonthinae) are known to defoliate pines. Some adults in these subfamilies are also attracted to sap flows.
The larvae of most scarab beetles develop similarly. Eggs are deposited by the adult female in suitable soil, dung, compost, or other organic material. After hatching, the C-shaped grubs feed and grow, molting twice. In areas with cold winters, larvae overwinter below the frost line. As temperatures rise in the spring, larvae become active and feed until pupation. Emergence of the adult from the pupa often occurs in response to environmental cues such as rainfall or temperature. After emergence, adults mate and begin the cycle anew. The biology and behavior of many species of scarabs is not known, and much remains to be studied. References: Ratcliffe 1991; Ritcher 1958; Woodruff 1973.
Form scarabaeiform (C-shaped, cylindrical), some hump-backed [Scarabaeinae]. Color creamy-white or yellow (except at caudal end which may be darkened by accumulated feces). Cranium heavily sclerotized, testaceous to brown to black. Antennae 4-segmented, last segment bearing 1 or more sensory spots. Ocelli absent, present [some Dynastinae, Cetoniinae, Trichiinae], or with distinct pigmented spots. Frontoclypeal suture present. Labrum at apex variable, rounded or lobed. Epipharynx rounded or lobed, asymmetrical. Maxilla with galea and lacinia distinctly separate [Aphodiinae, Scarabaeinae], fused proximally and free distally [Melolonthinae], or fused to form mala [Dynastinae, Rutelinae, Cetoniinae, Trichiinae, Valginae]; maxillary stridulatory area usually present; maxillary palpus 4-segmented. Abdomen with segments 9 and 10 fused dorsally [Cetoniinae], segments 1-6 or 7 usually with 3 annuli, each with 1 or more transverse rows of setae. Spiracles cribriform. Venter of last abdominal segment with or without fleshy lobes, apex with or without palidia, anal opening with transverse or Y-shaped slit. Legs 2-segmented [Scarabaeinae] or 4-segmented [Aphodiinae, Melolonthinae, Dynastinae, Rutelinae, Cetoniinae, Trichiinae, Valginae], lacking stridulatory process; claws present or absent with 1-2 setae. References: Ritcher 1966; Scholtz 1990.
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