The Life Cycle of Butterflies
Most students in elementary school learn about the butterfly life cycle due to its simplicity and the ease of being able to actually watch it happen in a relatively short period of time. There are plenty of ways to learn about the butterfly life cycle, including videos, websites, and even actually watching the cycle happen (there are plenty of butterfly kits to watch the life cycle). This paper will explain the life cycle of a butterfly, particularly the Monarch Butterfly, the only butterfly known to make a two-way migration each season like geese do, in four stages, the egg, the caterpillar, the chrysalis, and the adult butterfly of course.
In all butterflies the first stage of the life cycle is the egg. Eggs are laid by the female butterfly on the bottoms of leaves in large numbers in order to ensure the survival of a new generation. Some lay their eggs one at a time, others in clusters, and others a whole bunch (hundreds) at once. Sometimes the females may mate multiple times just to lay enough eggs. The Monarch Butterfly in particular lays its eggs on the bottoms of leaves belonging to the milkweed plant. Caterpillars, once they hatch from the egg, eat the plant’s leaves that they are on, so the Monarch caterpillars eat the Milkweed plant’s leaves. The eggs laid can be oval-shaped, spherical, or pod-shaped. All butterfly eggs are very small. In the Monarch’s case, the eggs are green, spherical eggs with ridges. A butterfly’s egg generally has three key parts, the micropyle, the yolk, and the chorion. The micropyle is a small hole at the top of the egg which allows air and water to enter the egg, allowing it to live. The yolk nourishes the egg and allows the larva inside to grow and develop. Lastly, the chorion is the hard shell that protects the egg from cracking. All three of these parts allow the egg to hatch into the larva, or caterpillar, within three to eight days.
Once the egg hatches the Caterpillar emerges. Caterpillars come in all sorts of shapes and sizes, from the Tomato Hornworm, a common garden pest, to the Saddleback Caterpillar, which is known for its saddle pattern on the back, to the famous Woolly Bear caterpillar that evokes superstition and freezes solid over the winter only to emerge and become a moth in the spring. The Monarch caterpillar, when it first hatches, is small and green, similar to the egg it hatched from, and is unrecognizable to the common observer. However, the Monarch caterpillar, along with all other caterpillars, molts, or sheds its skin and grows new skin to replace it. Each period in-between a molt is called an instar, and the Monarch has five instars. The small green caterpillar is the first instar, and this is the only instar where the Monarch caterpillar is green. The second instar is a caterpillar with yellow, white, and black bands. Also, little tentacles begin to grow on the thorax and abdomen. After the caterpillar molts a second time, the bands become more distinct and tentacles grow near the head. In the fourth instar, the pattern is slightly changed and white dots appear on the prolegs (previously tentacles) in the abdomen. The prolegs are small stubs found on the bottoms of caterpillars and other larvae with a fleshy structure. In the last instar all the prolegs get white spots and the pattern of white, yellow, and black bands gets more complex. There are a few important things to note before the life cycle continues to the next stage. The first is that the caterpillars make these changes while they molt. The second is that caterpillars grow tremendously between their first and last instar, at the first instar, the Monarch caterpillar is 2 to 6 millimeters long and ½ to 1 ½ mm wide. At the fifth and last instar, the caterpillar is 25 to 45 mm long and 5 to 8 mm wide, a remarkable difference. The last thing to note is predators. Caterpillars, especially ones in tropical areas, can be eaten by birds and wasps, but the ones who survive to the fifth instar start to eat a lot of food again for storing it while in a chrysalis, if they don’t, they will starve to death inside the cocoon.
The next stage in a butterfly’s development is the chrysalis. The chrysalis is a cocoon that a caterpillar develops in for around two weeks. The chrysalis generally is attached to a branch or the bottom of a leaf, and the caterpillar, before becoming a chrysalis, hangs in a j-shape. A silk pad attaches the chrysalis to the object, leaf or branch, above it. During its time as a chrysalis the butterfly is developing constantly every day to grow wings and new legs, just to name a few new features the butterfly will have. The Monarch chrysalis is green with a few yellow spots. The transformation from caterpillar to butterfly with the chrysalis is called metamorphosis. Around a day before the adult emerges, the chrysalis turns to a transparent shade, and the next day the butterfly emerges. This process happens in many species, including the Monarch.
The last stage of a butterfly’s development is the adult butterfly. After emerging from the chrysalis, the butterfly must hang and dry. Some butterflies take three hours to dry, and when drying they are vulnerable to predators. After the butterfly is dry it flies off and begins its life as an adult butterfly. The main purpose of an adult butterfly is to mate so another generation can exist. Butterflies’ life spans vary as adults, from a few days or weeks to several months, even within a species. The Monarch lifespan happens to vary within the species; the migrating generations can live up to nine months, while the early summer generation may only live for two weeks. The Monarch butterfly only has a few species of bird as predators, since the Monarch is toxic for most species to eat, including humans. This toxin comes from the Milkweed plant that it eats as a caterpillar, and the poison of milkweeds varies between each species. The Monarch migrates south to Mexico and California from areas like Canada, the Eastern coast of the U.S., and the Northwest U.S. The Monarch is the only butterfly to make a two-way migration like birds. This migration begins in the fall, where butterflies make a 2,000 mile journey south and overwinter in large groups containing tens of thousands of butterflies. The Monarch Butterflies appear to find their way using a combination of factors; the magnetic pull of the Earth and the position of the sun among other stars, both of which are of great use to the Monarch. The Monarchs overwinter in large groups so the butterflies can stay warm. Dangers include falling braches and predators such as birds and mice. Around 14% of all Monarch butterflies that overwinter in Mexico are eaten by birds and mice. When spring arrives, the butterflies migrate back north. The migration is shorter for some, who may only travel from British Columbia to Southern California, or even shorter, some travel from southern Florida to the Florida Panhandle.
In conclusion, the butterfly life cycle is a simple and easy one to understand and is great for student projects. The Butterfly life cycle beings when a female butterfly lays its eggs on the bottoms of leaves. These leaves serve as the caterpillar’s food source when it hatches from the egg. A butterfly’s egg has three main parts, the micropyle, which allows for air and water to enter the egg, the yolk, which nourishes the developing larva, and the hard chorion, or shell, that protects the egg. The Monarch lays its green, spherical (with ridges) on the bottoms of the leaves belonging to the milkweed plant. Once an egg hatches the caterpillar beings eating the leaves and molts multiple times, emerging slightly different after each molt. After the first molt, the caterpillar is in its second instar, or phase of development. The Monarch caterpillar goes through five instars, and, except for the first, has a characteristic black, yellow, and white pattern. In certain instars caterpillars emerge from the molt with new features such as tentacles and prolegs. After the last molt the caterpillar eats a lot of food and finds a spot to hang in a j-shape. Then the caterpillar begins its phase as a chrysalis, or cocoon, for around two weeks. During this time the caterpillar is hard at work at developing into a butterfly. The Monarch chrysalis is green with a few yellow spots. When the butterfly emerges it must dry before taking off into the world. When it flies off its main purpose is to mate so a new generation can survive. The Monarch butterfly is the only butterfly to migrate in two directions like Canadian Geese do. The Monarch migrates from areas such as the eastern coast of the U.S., the Northwestern U.S., and Canada, south to California and Mexico in the fall, and only the fourth generation completes a round trip. They cluster together in overwintering sites in the ten thousands to stay warm, however, sometimes branches from the trees they are overwintering on fall, and some of the butterflies are crushed. When spring arrives the butterflies migrate back north, they mate, and the life cycle repeats itself as it has been for many years.
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