Butterflies and moths have to be warm (77 to 79°F or 25 to 26°C) in order to fly. They depend on the temperature of their environment to maintain their body temperature. Butterflies living in cooler climates use their wings to warm their bodies. They bask in the sun so their wings get maximum exposure to the warm light. In hotter climates butterflies can overheat, so they are usually active only during the cooler parts of the day, early morning, late afternoon, or early evening. During the heat of the day they rest in the shade.
Some larger thick-bodied moths, such as hawk moths, can generate their own heat to a limited degree by vibrating their wings. The heat generated by the flight muscles warms the thorax, but the abdomen does not need to be kept so warm. To avoid overheating some moths rely on hairy scales, internal air sacs, and other structures to separate the thorax and abdomen and keep the abdomen cooler.
Butterflies, skippers, and moths usually get together only to mate. However, some species do gather in large groups to find a more comfortable climate. Only about 200 species of butterflies and moths regularly migrate long distances, returning to the areas where they breed. The Jersey tiger moth escapes the summer heat by gathering in large numbers in cooler, wetter habitats. Monarchs in North America migrate by the thousands or millions each year to the coast of California or the volcanic mountains of southern Mexico to escape cold winters. In spring they fly east from coastal California, or north from Mexico, laying their eggs on milkweeds as they go. Individuals seldom make the entire return trip. Instead, this is accomplished by their offspring. It takes three to five generations of monarchs each year to repopulate the continent. The last generation in late summer or early fall is the one that migrates to warmer climates.
Caterpillars display a wide range of defensive behaviors to avoid being eaten by birds and other animals. For example, bag-worms build a protective case of silk and cover it with twigs, leaf fragments, and sand. Others have colors and textures that help them blend in with surrounding twigs, leaves, and flowers. When startled, some species whip back and forth, rear up to expose large fake eye spots, vomit bright-colored fluids, or pretend to be dead and drop to the ground.
Both adults and larvae of some species have bright colors or distinctive patterns that warn predators of their bad taste. Other caterpillars are covered with irritating hairs or stinging spines. Giant leopard moths from the eastern United States are boldly marked insects with large black spots on a white background. When threatened they release a foul-smelling yellow fluid from special glands in their thorax. Mimics also have bright colors to fool experienced predators into thinking that they taste bad or are otherwise harmful. For example, some larvae mimic snakes in both appearance and behavior. Many day-active moths have slender black and yellow bodies with clear wings and resemble stinging bees and wasps. Bright warning colors are of little use to some night-flying moths, so they produce high-pitched sounds as part of their defense system that warns bats of their bad taste.
Male butterflies locate mates either by establishing and defending territories or by actively flying about the environment in search of females. They rely mostly on eyesight to find a mate but will also release pheromones (FEH-re-moans), or chemical scents that attract females. After locating a female the male will chase her until she drops to the ground. Depending on the species, before they mate he will move his antennae, flap his wings, and release pheromones from brushy tufts of hairs located on the thorax, wings, legs, or abdomen.
Most lepidopterans must mate to produce offspring, but some European bagworm moths reproduce by parthenogenesis (PAR-thuh-no-JEH-nuh-sihs), where caterpillars hatch and develop from unfertilized eggs. In moths, females release pheromones from their abdominal glands to attract males. The feathery antennae of some male moths are so sensitive that they can locate a female over a distance of several miles (kilometers). Courtship is usually very brief.
The life cycle of lepidopterans includes four very distinct stages: egg, larva (caterpillar), pupa, and adult. Females may lay their eggs singly or in batches inside plant tissues, glue them to all kinds of objects, or simply drop them from the air. In cooler regions the eggs may overwinter, or last through the winter, and will not hatch until the following spring or summer. The larvae molt, or shed their exoskeletons, or hard outer coatings, five or six times before reaching the pupal stage. Depending on the species, temperature, and the availability and quality of food, the time between egg and adult may take anywhere from fifteen days to two years. Mature larvae search for a suitable site to pupate.
Adults often emerge from their pupae right after rains. This way they can mate and lay their eggs at the same time plants are developing new leaves, providing the caterpillars with plenty to eat. Moths secrete a fluid to dissolve a hole in the cocoon or use sharp structures on their head to cut their way through the silk. Most adults live for a few days or weeks, but some species, such as migrating monarchs, live several months. Some species, such as mourning cloaks and several species of North American anglewings, overwinter as adults and fly in early February and March.
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