Arthropods 5a

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Southern California Arthropods (Mostly) #5: Beetles 1
© W.P. Armstrong 15 April 2009
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Long-Horned Beetle Family (Cerambycidae)

An adult pine sawyer beetle (Ergates spiculatus).
[Thanks to Jim Hogue at CSUN for the correct ID of this species.]

The pine sawyer is one of the largest beetles in urbanized areas of southern California. The large, pale larva, up to 2 1/2 inches (6.3 cm) long, feeds on the wood of fallen logs and old conifer stumps. The adult beetle in above photo is over 3 inches long (including the extended antennae). It has a pair of powerful jaws (mandibles) that are capable of inflicting a painful pinch. At least they can leave an imprint on a piece of cardboard! The adults emerge from subterranean stumps in early summer. They are nocturnal and are attracted to lights. It is always a surprise when one of these big beetles or the following beetle lands on your window screen.

Another long-horned wood-boring beetle (Prionus californicus). The
antennal segments of the male (in this photo) are conspicuously lobed.

California prionus (Prionus californicus).  The large larva feeds on roots of
deciduous trees. It is similar to the pine sawyer beetle (Ergates spiculatus).

See Close-Up View Of A Bark Beetle (Family: Scolytidae)

Phoracantha recurva, a long-horned wood-boring beetle introduced into southern California from Australia. According to A. V. Evans and J. N. Hogue (Field Guide to Beetles of California, 2006), it was first discovered at the University of California at Riverside in 1995. Another closely related species (P. semipunctata) was found in 1984 on dying eucalyptus trees in Orange County. The larvae of both species tunnel between the bark and wood, but construct their pupal chambers in the heartwood. Adult beetles are attracted to fallen branches and injured or water-stressed trees.

More Images Of Eucalyptus Wood-Boring Beetle

Hypexilis pallida, another long-horned wood-boring beetle in San Diego County.

This deceased beetle was found in the water dish of a carpenter ant terrarium containing a dead limb from my backyard. It undoubtedly emerged from the dead limb. I originally misidentified it because I didn't realized it had long antennae.

Scarab Beetle Family (Scarabaeidae)

An adult ten-lined june beetle (Polyphylla decemlineata).

This is a large beetle with conspicuous white stripes on its wing covers (elytra). When taking off, the elytra move forward and a pair of larger, membranous flight wings unfold. The beetle is attracted to lights at night during the summer evenings in southern California. When handled it makes an unusual squeaking sound. Adult beetles feed at night on needles of coniferous trees.

Rain Beetles In Twin Oaks Valley, San Diego County
Several species of large scarab beetles (family Scarabaeidae) appear with the first soaking rain during late fall in coastal San Diego County and adjacent Baja California. They belong to the genus Pleocoma and are commonly referred to as rain beetles. The name Pleocoma is derived from two Greek roots, "pleos" (full or abundant) and "kome" (hair). The name translates into "very hairy," which describes these beetles perfectly, particularly their underside. Rain beetles are typically found in coastal foothills and canyons of chaparral and coastal sage scrub. After a soaking rain (usually one or more inches), male beetles make a sudden appearance at dusk, early morning, or on cloudy, drizzly days. The males fly in slow sweeping arcs throughout the foothills, keeping close to the ground in search of the larger, flightless females. They are attracted by a pheromone (chemical sexual attractant) emitted by the female as she waits at the surface of her subterranean burrow. The males are also attracted to lights and often bump into windows of houses in foothill areas. Since adult beetles do not feed, the male only has an energy reserve for a flight of a few hours before he literally runs out of "gas."

Male black rain beetle (Pleocoma puncticollis), a large scarab beetle that appears with the first soaking rain in San Diego County. The flattened, bilobed extension of the head (clypeus) is used for scooping soil as he pushes through the ground. The underside of the body is covered with dense black hair.

The larger, more rotund, flightless female rain beetle rarely leaves her burrow in the ground. She emits a pheromone that is apparently irresistible to the male, as she waits for him at the surface of her burrow. After mating, the female closes the entrance and lays eggs at the base of her burrow. Like the male, she is equipped with a rigid digging device at the end of her head called a clypeus. Both sexes of Pleocoma lack functional mouthparts and digestive tracts, and consquently do not feed during their brief adult life. With her powerful legs and clypeus, the female pushes and scoops the soil like a miniature bulldozer. Her eggs do not mature until the following spring or early summer.

A female rain beetle (Pleocoma sp.). She is larger than the male and spends most of her life below ground in her burrow. Like the male, she has a very hairy underside and is equipped with powerful legs and a sturdy clypeus on the front of her head.

Rain beetle larvae hatch from eggs deep in their mother's subterranean burrow. They are slow to develop, and have a life cycle lasting ten years or more. They feed on roots, fungal hyphae and other organic debris, eventually metamorphosing into adults. Adult males may wait a month or more before the first rains bring them into the open air for their mating flight. During this time, the females dig to the surface and wait for the males to arrive. Neither male nor female rain beetles feed as adults, their short adult life provides the vital transfer of genes and perpetuation of these remarkable species of beetles.

A deceased male rain beetle who apparently ran out of energy.

A metallic green fig beetle (Cotinus texana), so named because it is often found feeding on fig fruits during the warm summer months in southern California. It is also fond of other ripe, juicy fruits, such as peaches and plums. These attractive beetles spend their juvenile larval stage in the ground, often beneath manure piles, compost and haystacks.

A metallic green fig beetle (Cotinus texana) gorging itself inside a fleshy, ripe syconium of the Calimyrna fig (Ficus carica). Although masses of minute, aggressive Argentine ants (Iridomyrmex humilis) are also foraging in the syconium, the beetle is protected by a tough, impervious exoskeleton.

See: Beware Of The Argentine Ants

"Little Bear" (Paracotalpa ursina).

Darkling Beetle Family (Tenebrionidae)

Darkling beetles of the genus (Eleodes). These large, ground-dwelling beetles have fused wing covers (elytra) and cannot fly. They are sometimes called "stink beetles" because some species apparently emit an odor when handled; however, I have never observed any disagreeable odor in the docile species shown in the above images. When disturbed or threatened they exhibit the unusual behavior of raising their abdomen into the air. This "headstanding" alarm posture has earned them the name of "acrobat beetle."

Eloedes With An Odor

An Eloedes beetle in its characteristic "headstanding" alarm posture. Unlike most of the Eloedes beetles I have observed, this one definitely released a slightly disagreeable odor.

Ironclad Beetles (Phloeodes pustulosis). These ground-dwelling beetles have fused wing covers (elytra) and cannot fly. They are fairly common in southern California. The common name is derived from their very hard body wall that can resist a sharp insect pin. When disturbed or threatened they retract their legs and antennae and remain motionless. They are thought to feed on decaying, fungus-ridden wood.

Apsena sp. in the family Tenebrionidae, subfamily Tenebrioninae, Tribe Eulabini. Found at the summit of Owens Peak northeast of Palomar College, San Marcos, CA.

Rove Beetle Family (Staphylinidae)

This is not a large ant. It is a rove beetle, sometimes called the Devil's coach horse(Staphylinus olens). These large, ground-dwelling beetles have short wing covers (elytra) and do not fly. When alarmed it exhibits a threat posture by opening its formidable mandibles and raising the tip of its abdomen (right image). Although the abdomen has no stinging device, this display serves to ward off enemies. The alarm posture is well deserved because this beetle can inflict a painful bite into your finger. Two glands at the tip of the abdomen emit a malodorous yellowish liquid. Both adults and larvae are voracious predators. According to C.L. Hogue (1974 & 1993), Insects of The Los Angeles Basin, this beetle feeds on garden snails and slugs. Although it was originally introduced from Europe around or before 1931, it is probably beneficial in your garden.

Ground Beetle Family (Carabidae)

Common calosoma (Calosoma semilaeve), a large beetle that runs free during daytime hours in search of prey. With its long cursorial legs it runs very fast. When disturbed or threatened it emits a foul oder that smells like burning electrical insulation.

See Another Long-Legged Calosoma Beetle

Larva of a ground beetle (Carabidae) from Anza-Borrego Desert.

Ground beetle and larva of the genus Calosoma in the family Carabidae. This predaceous genus is often called "caterpillar hunter." During April of 2005, the carabid larvae were very abundant in Anza-Borrego Desert feeding on the pupae (chrysalises) of the painted lady butterfly (Vanessa cardui). Note: In moths and butterflies that do not spin cocoons, the hard-shelled pupa is called a chrysalis.

See Painted Lady Butterfly

Laemostenus complanatus, a fast-running, predatory carabid beetle. Although native to northern Africa, this beetle is fairly common in southern California. It has been introduced around the world, including the Mediterranean region, western North America, southern South America, and parts of Australia and Tasmania.

Stag Beetle Family (Lucanidae)

Cottonwood stag beetle (Lucanus mazama).

Carrion Beetle Family (Silphidae)

A carrion beetle of the family Silphidae, also known as the black burying beetle (Nicrophorus nigrita). According to James N. Hogue (Introduction to California Beetles, 2004), Nicrophorus demonstrates the most advanced behavior of parental care known in beetles. These beetles bury small animal carcasses to reduce competion with flies, ants and other carrion-feeding insects. This insures food for the beetles and their larvae. In addition, they use their sensitive red antennae to detect hydrogen sulfide and cyclic carbon compounds that are released from decaying carcasses.

Snout Beetle Family (Curculionidae)

There are some animal species with only females in the population. One of these is Fuller's rose weevil (Naupactus cervinus = N. godmanni = Asynonychus godmanni ), a small flightless, broad-nosed weevil introduced into California from South America in the late 1800s. This beetle feeds on many cultivated plants and is especially troublesome in citrus groves where the adults eat new growth on young trees. The larvae feed on roots and make furrows in the bark. Eggs are laid on citrus fruits under the green calyx, and are transmitted during the shipment of infected fruits. Males have never been found in this species, so the females must produce viable eggs without fertilization, a phenomenon known as parthenogenesis.

Fuller's rose weevil (Naupactus cervinus). Each generation is composed of only females (thelytokous) that come from the same mother. According to Benjamin Normark (1996), parthenogenetic weevils are apomictic; meiosis does not occur and all female offspring are genetically identical to their mothers, except for mutations. Traditionally, hybridization and polyploidy were the main explanations for the origin of asexuality in weevils; however, Marcela Rodriguero, et al. (2010) suggests another possible explanation: the parthenogenisis inductor bacterium Wolbachia pipientis. The endosymbiont bacterial genome can produce drastic consequences on the evolution of its host species, such as extinction or sex role reversal.

  1. Normark, B.B. 1996. "Phylogeny and Evolution of Parhenogenetic Weevils of the Aramigus tessellatus Species Complex (Coleoptera: Curculionidae: Naupactini): Evidence From Mitochondrial DNA Sequences." Evolution 50 (2): 734-745.

  2. Rodriguero, M.S., Lanteri, A.A., and V.A. Confalonieri. 2010. "Mito-Nuclear Genetic Comparison in a Wolbachia Infected Weevil: Insights On Reproductive Mode, Infection Age and Evolutionary Forces Shaping Genetic Variation." BMC Evolutionary Biology 2010, 10:340.


  1. Borror, D.J. and D.M. DeLong. 1964. An Inroduction To The Study of Insects. Holt, Reinhart and Winston, New York.

  2. Evans, A.V. and J.N. Hogue. 2006. Field Guide to Beetles of California. University of California Press, Berkeley, California.

  3. Evans, A.V. and J.N. Hogue. 2004. Introduction to California Beetles. University of California Press, Berkeley, California.

  4. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

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