BRISTLETAILS: Microcoryphia

PHYSICAL CHARACTERISTICS

Bristletails are true insects that never develop wings. They have young that look just like the adults. Their mouthparts, unlike those of diplurans, proturans, and collembolans, are not hidden inside a pocket in the head. They range in size from 0.3 to 0.8 inches (7 to 20 millimeters), not including their tails. The thorax, or midsection, is divided into three sections, each with enlarged upper and lower plates, giving the bristletail a humpback or teardrop shape. The entire body (head, thorax, and abdomen) is covered with flat scales. The head has a pair of long, threadlike antennae (an-TEH-nee), or feelers, and long, leglike mouthparts that look much like a fourth pair of legs. The large eyes consist of many lenses.

The ten-segmented abdomen is tipped with three long, bristlelike tails that are held straight out from the body. All but the first abdominal segments have paired structures underneath that help support the abdomen and keep it from dragging on the ground. Most of the abdominal segments usually have special sacs underneath that help attach the bristletail to the ground so that it can molt, or shed its external skeleton.

GEOGRAPHIC RANGE

Bristetails are found on all continents except Antarctica.

HABITAT

Bristletails are found on the soil, in leaf litter, under rocks, and on stumps and logs from sea level to 15,750 feet (4,800 meters) in the Himalayas. Species living in tropical rainforests often spend some or all of their time high up on the trunks and limbs of trees.

DIET

Bristletails eat dead leaves; algae (AL-jee); funguses; and lichens (LIE-kuhns), which are plantlike growths of funguses and algae growing together.

BEHAVIOR AND REPRODUCTION

The majority of species are active early in the evening or at night. Different species living in the same habitat sometimes group together in sheltered habitats. Bristletails seem to follow certain routes as they search for food, suggesting that they are following trails of chemicals laid down by other bristletails.

Bristletails jump by bending their bodies and then suddenly releasing the tip of the abdomen so that it hits the ground. They are excellent climbers, using their paired abdominal structures to grip vertical surfaces as they climb like inchworms.

Males and females engage in lots of touching with their antennae during courtship. Depending on the species, the males use a variety of methods to transfer their sperm to the female. In some species the male lays a silk thread on the ground. He deposits sperm on the web, which is later collected by the female. The males of other species attach a sperm packet to the ground and then guide a female over it. Still other species mate, with the male depositing sperm directly into the female's body.

BRISTLETAILS VERSUS SILVERFISH

With their shiny, scaly bodies, bristletails closely resemble silverfish (order Thysanura). Bristletails, however, have tube-shaped bodies, while those of silverfish are flattened. The eyes of bristletails are quite large and meet over the top of the head, but those of silverfish are much smaller and are widely separated. And each jaw of a bristletail has only one point of attachment to the head, while those of silverfish and all other insects connect to the head at two points.

Females lay their eggs in protected places, usually gluing them to the ground. Young bristletails molt six to eight times before reaching adulthood. Adults continue to molt and grow for the rest of their lives and are able to replace lost limbs and other structures as they molt. Bristletails may live up to three years and molt as many as sixty times.

BRISTLETAILS AND PEOPLE

Bristletails do not directly affect people or their activities.

CONSERVATION STATUS

No bristletails are threatened or endangered.

NO COMMON NAME (Petrobius brevistylis): SPECIES ACCOUNT

Physical characteristics: The body is as long as 0.43 inches (11 millimeters), not including the antennae and tails. Each of these structures is nearly as long as the body. They are covered with silvery gray scales, mixed with scattered patches of black scales. The antennae are completely covered with dark scales.

Geographic range: The species is originally from northern Europe and has since become established in northeastern North America.

Habitat: This bristletail is most common above the high-tide line along rocky seacoasts, living among cliffs and boulders. They prefer steep surfaces with few cracks and little loose sand. They also are found on buildings in northern Europe.

Diet: This species grazes on algae, lichens, and mosses growing on rocks.

Behavior and reproduction: Individuals forage, or search, for food on the surfaces of cliffs and among boulders. They hide in cracks among the rocks or under stones.

During courtship, bristletails have very little contact. Males deposit sperm directly into the female's body. In some populations there may be very few males or no males at all, and the females can reproduce without mating. The eggs are soft and are squeezed into cracks in the rocks. After hatching, the larvae (LAR-vee), or young, take about three or four months to reach adulthood. Adults may live up to three years.

Petrobius brevistylis and people: Bristletails do not directly affect people or their activities.

Conservation status: This species is not threatened or endangered. ∎

FOR MORE INFORMATION

Web sites:

"Archaeognatha, Bristletails." Tree of Life Web Project. http://tolweb.org/tree?group=Archaeognatha&contgroup;=Insecta%20 (accessed on September 2, 2004).

"Insects and Their Allies: Archaeognatha: Bristletails." CSIRO Entomology. http://www.ento.csiro.au/education/insects/archaeognatha.html (accessed on September 2, 2004).

"Jumping Bristletails." http://www.ent3.orst.edu/moldenka/taxons/Petrobius.html (accessed on September 2, 2004).