The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Thursday, April 09, 2009

Butterfly Development is Nothing Short of a Miracle
by Ro Wauer

Monarchs have been passing through the Victoria area for several weeks now. Some mornings a dozen or so lift off as soon as the sun hits them, they may cruise about the yard for a time, nectar on a few flowers, and then continue their northward journeys. By afternoon, some of those individuals spend a little more time, sampling the flower nectar, and some of the females find a milkweed plant (foodplant) on which she lays eggs. It reminds me once again of the miracle of butterfly metamorphosis.

Butterfly development from egg to larva, caterpillar to pupa, or chrysalis to adult butterfly is truly remarkable. Butterfly life history is one of nature’s most amazing happenings. And as the spring and summer months descend upon us, that miracle is all around, for all of us to see and appreciate.

All butterflies have a life cycle that is called complete metamorphosis because it includes four stages. Butterfly eggs are tiny things that can be round, spherical, or bun-shaped and may come singly, in small clutches, or in huge masses of up to 50 eggs that are attached by a gluey substance. The eggs are laid on a plant that the hatched caterpillar can utilize as a food source. The eggs can be laid on top or beneath a leaf, on a twig, or even at the base of grass, depending on the butterfly species.

Hatching can take anywhere from a few days to a full year, again depending upon the species. For instance, falcate orangetip butterflies fly only from March into May, during which time they lay eggs and live as larvae; the remainder of the year they occur only as chrysalides. However, most butterflies we see during the year pass through the four stages in only a few weeks, and so we see fresh specimens constantly during the warmer days of the year.

Butterfly larvae, or caterpillars, are true eating machines that spend the majority of their existence consuming plant materials; the exception is the harvester butterfly larvae that feeds on aphids. The body of a caterpillar is divided into the three parts: head with a pair of simple eyes, mouth, and large jaw (mandible); thorax, with three segments containing three pairs of legs for moving about; and abdomen, with ten segments containing five pairs of prolegs, built like suckers to aid in clinging to various materials. The jaws not only can tear plants apart but also assist in transporting food to the mouth. This eating machine’s entire purpose is to convert plant or animal tissue into butterfly tissue.

Like all arthropods, the butterfly caterpillar grows by shedding its skin periodically, whenever the new exoskeleton develops and hardens underneath. Once the new exoskeleton is formed, the caterpillar breathes in extra air and splits the old outer skin down the middle, and simply crawls out of its old skin. This process is called molting.

Finally, when the caterpillar reaches its maximum size, it finds a safe location and spins a form of silken mat, often with a silken thread or girdle as a safety belt. It then hangs upside down and spins a silken sheet, not a cocoon (only moths spin a cocoon), on a leaf or other object. This time, when shedding its old skin, it changes into a chrysalis, an immobile stage in which it undergoes a massive reorganization. This transformation takes a week to several months, depending on the species and the time of year, and includes both internal and external organs.

Its emergence as an adult butterfly is one of Mother Nature’s most incredible feats, going from caterpillar to butterfly, complete with small wings and an oversized body. On emergence, it quickly pumps fluid into the wings from the body that then shrinks to its normal size. The adult has also developed a proboscis (a long coiled suction tube for feeding) and six true legs. Emergence usually occurs in the early morning when humidity is high, temperatures are relatively low, and predators are less active. The first flight usually occurs in the afternoon.

Adult butterflies must have food and water to continue their life process, so they feed on nectar and pollen from various flowers and often also obtain water and nutrients from various sources such as rotting fruit, carrion, dung, and wet soil.

Butterfly courtship involves a rather complex behavior, involving recognition of the opposite sex by wing pattern and pheromones. Pairs often go sailing high in the air in courtship flights. Mating can continue for several hours, but then the female must find suitable plant species on which to lay her eggs. Once she lays her eggs, the process of transformation from egg to adult butterfly begins over again.

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