Beetles and Weevils: Coleoptera

Some plant-feeding beetles will nibble only the edges of leaves, while others will eat everything. Japanese beetles skeletonize leaves by eating all the soft tissue and leaving behind a network of leaf veins. Species feeding on plants with poisonous or sticky sap must first bleed the leaf of these harmful fluids. Before feeding they will bite the veins supplying the sap to the leaf to cut off the supply of sap and bleed the tissues they are about to eat.

Many predatory species will eat anything they can catch and usually choose to live in habitats where there is plenty of prey. Ground and tiger beetles capture their prey on the run, killing and tearing them into smaller chunks with large and powerful mouthparts. They attack a broad range of beetles, other insects, and invertebrates (in-VER-teh-brehts), or animals without backbones, although some prey only on snails. Many rove and clown beetles hunt for food among the nooks and crannies of leaf litter or in decaying plants or dead animals.

Other species are quite particular about what they eat and have very specialized behaviors for locating their prey. The larvae of fireflies feed only on snails and track down prey by following their slime trails. Checkered and bark-gnawing beetles eat bark beetles. They probably follow the scent of bark beetle pheromones to find them under bark. Ant-loving scarabs eat ant larvae and the nest by following the smell of ant pheromones back to the nest. Whirligig beetles identify prey by using waves across the surface of the water generated by struggling insects.

Aquatic beetles must regularly capture new supplies of fresh air to remain under water. Water scavengers do this by breaking through the surface headfirst. Using their antennae to break through the water surface, they draw a layer of air over their body and store it on the lower surface of their abdomen. Predatory diving beetles break through the surface with the tip of their abdomens to trap an air bubble under their elytra. When the oxygen supply of the bubble is nearly exhausted, the beetle must return to the surface for more air.

Beetles defend themselves from predators with a variety of structures, behaviors, and chemicals. For example, many large scarabs, stag beetles, and longhorns avoid being eaten by simply being too large or frightening in appearance. Sharp horns and big, powerful jaws protect others. Beetles with flat bodies will retreat into tight spaces to get out of reach of predators. Shiny, metallic colors and bold patterns make some species look less beetle-like so they are overlooked by predators. Many weevils and other beetles are plain in color or have blotchy patches of browns, blacks, and grays that make them almost invisible on a background of tree bark. Some beetles are protected because they look or behave as, or mimic, stinging wasps, bees, or ants. The chemical weapons of beetles are produced by special glands or taken directly from their food. These foul-smelling and bad-tasting chemicals are released as sprays from the tip of the abdomen, or dribbled out of leg joints. Bombardier beetles spray a burning, stinging fluid from their abdomens with surprising accuracy. Ladybugs, blister and soldier beetles store defensive chemicals in their blood and release them through their leg joints when attacked. Beetles that feed on toxic milkweeds sometimes use its chemical defenses as their own by storing the plant's chemicals in their own tissues.

Beetles communicate with each other using physical, visual, or chemical means, usually to find a mate. Many species use sound to locate one another. Bess beetles, longhorns, and bark beetles rub parts of their bodies together to make a squeaking sound. Male death-watch beetles bang their heads against the sides of their wooden tunnels to attract females. South African tok-tokkies drum their abdomens against soil and rocks to attract mates.

The best known form of visual communication among beetles is bioluminescence (BI-oh-LU-mih-NEH-sens), or light produced by living organisms. Fireflies produce flashes of light with special tissues in their abdomens to locate and attract mates. The speed and length of each flash is caused by a controlled chemical reaction. Each species has it own light-flashing pattern. The number and speed of the flashes help males and females of the same species to recognize one another. Males typically fly at night, flashing their lights until they see a female respond with her own signal. Upon locating a female, he continues flashing and flies toward the female's signal.

Most beetles depend on chemical communication, or pheromones, to find distant mates or those hidden nearby among tangles of vegetation. Females usually produce pheromones to attract males. Large numbers of males and females may gather in mating swarms, or leks (lehks), to improve their chances of finding a mate. Some beetles find mates at food sources, such as dead animals, animal waste, sap flows, or flowers. Others gather around open patches of ground, rocky outcrops, or lone sign posts. Horned males stake out sapping wounds on a tree or some other food source and wait for the arrival of a hungry female. They use their horns to defend the site against other insects, especially other males of the same species.

Most beetles must mate to reproduce. A few species are capable of parthenogenesis (PAR-thuh-no-JEH-nuh-sihs), or the process by which larvae develop from unfertilized eggs. Courtship behavior in beetles is uncommon. Male ground, tiger, and rove beetles may grasp the female's thorax with their jaws before mating, while some male blister beetles tug on the female's antennae. In most beetles the males simply climb on the back of the female to mate. They may stay there for some time in order to keep other males from mating with her. Males usually mate with several females if they have the opportunity. Females mate just once or with many males.

The life cycle of beetles includes four very distinct stages: egg, larva, pupa, and adult. In a few species of beetles the eggs are kept in the female's body until they hatch. However, most species lay their eggs singly or in batches. Beetles living on the ground simply drop them on the dirt, scatter them in soil rich in decaying plant materials, or place them in or near piles of decaying animal bodies or waste. The eggs of plant-feeding species are placed at the base of suitable food plants, glued to stems and leaves, or placed in the crevices of bark. Others place their eggs inside leaf tissues.

The larvae look nothing like the adults and rarely live with them. They scavenge dead animals and waste, attack roots, tunnel in plant tissues, or bore through wood. The larvae usually molt, or shed their exoskeletons or hard outer coverings, three or more times over a period of weeks or years before reaching the pupal stage. Beetle pupae are usually tucked away in soil or rotten wood, under stones, or inside plant tissues. In cooler climates, most beetles spend the winter in the pupal stage. In some beetles, such as many fireflies, the adult females lack wings and look just like the larvae. But they do have compound eyes and are capable of mating and reproducing. One or more generations of beetles are produced per year, depending on species and climate. Most adults live for weeks or months, but some desert darkling beetles are known to live ten or more years.

Parental care is uncommon among beetles. Some ground beetles build small pits to lay their eggs in and guard and clean them until they hatch. The females of several species of tortoise beetles will guard their eggs and larvae until they pupate. Bess beetles tunnel in rotten wood and live in dense colonies. They make squeaking sounds to communicate with other adults and larvae. The larvae depend on the adults for food. They only eat wood that has already been chewed or digested by the adults. In Europe some female rove beetles maintain and defend their brood tunnels and provide their larvae with algae (AL-jee) to eat. Bark and ambrosia beetles grow a special fungus that is eaten by adult beetles and larvae.

The males and females of some species, such as earth-boring beetles, dung scarabs, and burying beetles, cooperate with their mates to dig nests for their eggs and supply them with animal waste or dead animals. Other insects, such as flies, ants, mites, and other beetles, also compete for these food sources. Dung beetles reduce competition by burying animal waste in underground nests. These specially built tunnels help to keep the waste moist and fresh.

Burying beetles demonstrate the most advanced parental care known in beetles. Males and females bury small, dead animals in an underground chamber and prepare them as food for their young. They chew off the feathers or hair and shape the body into a pear-shaped mass with a small pit on top. They lick the mass to coat it with special chemicals that prevent it from decomposing. The female lays her eggs on the chamber floor, and they soon hatch. Both adults nibble on the mass and spit up fluids into the pit. Females call the young to the pit to feed with a squeaking noise made by rubbing the edge of their elytra against the abdomen. Both adults remain in the chamber until the larvae pupate.