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The Amazing Insects Known As Beetles

The earliest known prehistoric beetles date back about 230 million years ago, a time when dinosaurs roamed the earth. With the advent of flowering plants about 65 million years ago, speciation in beetles occurred at an astronomical rate as they began to exploit the rapidly evolving angiosperms. Hard bodies of beetles preserve very well, and fossil records of beetles are found throughout the evolution of flowering plants. One of the most interesting locations for beetle fossils is the La Brea formation at Mckittrick, California where numerous Pleistocene animals became entomed in tar pits over 10 million years ago. The tar pits were formed as crude oil seeped to the surface through fissures in the earth's crust. Evaporation of the oils resulted in a thick, sticky substance resembling asphalt. Some of the beetles embedded in these formations are perfectly preserved in every detail.

Volumes have been written about the amazing world of beetles. Adult short circuit beetles (Scobicia declivis) bore into lead sheathing of telephone cables causing short circuiting when moisture enters the small holes. Trunks of native California fan palms in the southwestern U.S. often contain large circular tunnels, the work of huge boring larvae (Dinapate wrightii), a member of the family Bostrichidae. The hardwood floor beneath a palm trunk section at the San Diego Museum of Natural History was deeply grooved by one of these larvae. The adult beetle is truly bizarre. In the late 1800's museums paid up to $1,000 to an enterprising collector for one of these striking beetles. The collector (probably a business major) reportedly inflated the value of his merchandise by keeping their exact location a secret.

Bombardier beetles (Brachinus spp.) inject an explosive mixture of hydroquinone, hydrogen peroxide plus several potent catalysts into a reaction chamber in the abdomen. Catalase breaks down the hydrogen peroxide into water and oxygen gas. Peroxidase oxidizes hydroquinone into benzoquinone. The mixture of chemicals and enzymes volatilizes instantly upon contact with the air, generating a puff of "smoke"" and an audible popping sound. This caustic flatulence is totally controlled by the beetle, otherwise it might accidentally blow up its rear end. The explosive discharge apparently discourages predators, either by chemical irritation, heat or repugnance. The temperature of the explosive mixture of gasses and fluids is over 100 degrees Celsius, the boiling point of water. This astonishing chemical defense mechanism is discussed by D.J. Aneshansley and T. Eisner (1969) in Science Vol. 165: 61-63.

The body fluids of some blister beetles of the family Meloidae contain cantharidin, a substance that causes severe irritation and blistering of skin. This chemical is very sensitive to mucous membranes and is the active ingredient of "Spanish-fly," made from the ground up bodies of a European blister beetle (Lytta vesicatoria) . Although it has been used as a counterirritant, its use as an aphrodisiac is very unwise unless you are raising livestock or chickens.

The pine sawyer is one of the largest beetles in urbanized areas of southern California. It belongs to the long-horned beetle family (Cerambycidae) 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 lands on your window screen.

Another large beetle attracted to lights during summer nights in southern California is the ten-lined june beetle. It belongs to the large scarab beetle family (Scarabaeidae). This striking beetle has 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 makes an unusual squeaking sound when it is handled. Adult beetles feed at night on needles of coniferous trees.

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."

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.

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.

Some beetles exhibit some rather peculiar behavior. Tumbling flower beetles (Mordella marginata) inhabit flowers and make some rapid tumbling movements to avoid capture. You would probably do some acrobatics too if you had a large spider after you. Dung beetles (Canthon laevis) spend much of their time rolling around a large ball of dung. Actually, this is very much like some of our jobs. Large, ground-dwelling beetles of the genus Eleodes (family Tenebrionidae) are commonly found wandering in the coastal mountains and deserts of southern California. 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."

This small, colorful rove beetle is distributed throughout the UK. Paederus species are widely distributed around the world. They are much more brightly colored than other rove beetles, with metallic blue- or green-colored elytra and many with bright orange or red on the pronotum and segments of the abdomen. These bright colors may be an example of aposematism (warning coloration), a signal to deter potential predators. These beetles are well-known for causing blistering dermatitis or rashes (erythemas) in people, including cases of epidemic proportions throughout the Old World. There is a lot of information about these fascinating beetles on the Internet. The following is summarized from Wikipedia: Due to toxins in the body fluids (hemolymph) of some species within this genus, the name "paederus dermatitis", has been applied to these beetles. In fact, a scholarly paper in The Lancet (2002) suggested that a Paederus species could have been responsible for some of the ten Plagues of Egypt described in the Bible's Book of Exodus. According to Medical and Veterinary Entomology (2009), at least 20 of the more than 600 species of Paederus beetles have been associated with paederus dermatitis, even though Paederus beetles do not bite or sting. This skin irritation results from contact with pederin, a vesicant (blister causing) toxin in the hemolymph (blood) of many females in the genus Paederus. The toxin is manufactured, not by the beetles themselves, but by endosymbiont bacteria, probably a species of Pseudomonas. The following is from Journal of Venomous Animals & Toxins Including Tropical Diseases (Feb. 2015): Rove beetles of the genus Paederus cause dermatitis when they come in contact with human skin. This condition is prevalent in some tropical and subtropical regions, such as northern Pakistan, where it was recorded for the first time by U.S. troops. Paederus species are widely distributed around the world. They are much more brightly colored than other rove beetles, with metallic blue- or green-colored elytra and many with bright orange or red on the pronotum and segments of the abdomen.

Paederus littoralis A stamp commemorating this remarkable rove beetle on a French postage stamp. Accessed on Wikipedia 22 May 2022.

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 weevil introduced into California 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.

The Chrysomelidae is a large family of leaf-eating beetles. Although some chrysomelids can cause serious damage to plants, there is one species that truly appears like a glistening golden droplet in your garden. This stunning, metallic gold beetle is slightly smaller than a ladybird beetle. It is called the golden tortoise beetle (Metriona bicolor). The sides of the thorax and elytra are flared out and extend beyond the body, thus hiding the head and much of the legs. This extended covering is the derivation of the name "tortoise beetle" or "turtle beetle." Although collected in Escondido (San Diego County), the golden tortoise beetle is relatively uncommon in southern California. It is more common in the eastern United States. Both adults and larvae feed on the leaves of morning-glories (Convolvulaceae) and related plants. In the case of the aggressive, fast-spreading bindweed (Convolvulus arvensis), this little beetle could actually be beneficial. In order to capture their beautiful golden luster, these beetles should be photographed alive. The color appears especially brilliant during mating season. On dead beetles the golden luster fades rapidly.

View The Official Wayne's Word Fun With Beetles Page.    View A June Beetle In Flight. The two leathery elytra are spread apart to reveal the unfolded, membranous fight wings.    View A Genuine Beetle Body Necklace.    View An Enormous Hercules Beetle From Costa Rica.    View A Pizza Graph Showing The Percentage Of Beetle Species Compared With All The Species Of Plants And Animals On Earth.    Try Your Luck At Finding All The Beetles In A Beetle Word Puzzle.    Answers To The Beetle Word Puzzle.

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