Conservation Status

The World Conservation Union (IUCN) lists 303 species of lepidopterans, 176 of which are listed as Critically Endangered, Endangered, or Vulnerable. Critically Endangered means facing an extremely high risk of extinction in the wild; Endangered means facing a very high risk of extinction in the wild, and Vulnerable means facing a high risk of extinction in the wild. The United States Fish and Wildlife Service also lists twenty-five of these species, mostly butterflies, as Endangered, or in danger of extinction throughout all or a significant portion of their range. Giant birdwing butterflies and other species are listed by the Convention on International Trade in Endangered Species (CITES).

Butterflies are familiar animals that attract considerable at tention. Unlike most insects, they are admired and appreciated by the general public. Because of this, many species have been given protection by local, state, national, and international agencies. Butterfly collecting is often thought to be the most serious threat to their populations, but this is simply not true. As with all species, it is the destruction of their habitats that makes them vulnerable to extinction.

SILKWORM

Bombyx mori

SPECIES ACCOUNTS

Physical characteristics: Mature caterpillars measure 1.5 inches (40 millimeters) and are grayish with brown marks on the thorax. They have a short horn near the tip of the abdomen. They spin a white or yellow cocoon for pupation. The color of the cocoon is determined by heredity and diet. The cocoon is made from one continuous silk thread that measures 1,000 to 3,000 feet (300 to 900 meters) long. The whitish adults are heavy bodied, rounded, and furry. Adult wingspan is 1.5 to 2.5 inches (40 to 60 millimeters). The forewings are hooked at their tips.

Geographic range: This species is originally from the north of China, the north of India, Japan, Taiwan, and Korea. They are now raised commercially in Europe and North and South America.

Habitat: The silkworm is the world's only completely domesticated insect. No populations are found in the wild. They are raised on farms near fields of mulberry trees.

Diet: Caterpillars feed only on mulberry leaves. The adults have no mouthparts and do not feed.

Silkworms are now raised commercially in Europe and North and South America. (©Pascal Goetgheluck/Photo Researchers, Inc. Reproduced by permission.)

Behavior and reproduction: The adults cannot fly. The domesticated larvae can survive only with human assistance.

Females lay 200 to 500 lemon-yellow eggs that eventually turn black. The eggs hatch in spring. The larvae molt four times in four to six weeks before spinning a cocoon. The mature caterpillar spends up to three or more days to spin an entire cocoon. Adults emerge in about three weeks, mate, and die in about five days. There is usually only one generation per year.

Silkworms and people: Silkworms were first domesticated in China. They are now raised for educational purposes in classrooms as well as to harvest their silk. The silk is obtained by boiling the cocoons in water to kill the pupa and unraveling the thread. Dead pupae are sometimes used as cockroach bait, fish food, or as fertilizer for mulberry trees.

Conservation status: This species is not considered endangered or threatened. ■

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