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What's bugging you? Jan. 30, 2019

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Did you ever wonder where insects come from? And did you ever question how insects grow up? Like us, most start out as an egg but from that point on boy are they different!

As mammals, we start as an egg in our mother's womb and develop into a baby. When born, we are still babies, at least for the first years of our lives. Then we get called toddlers, then boys and girls, then teens, then young adults, adults and then old adults. I will admit that I am presently in the last category.

While the life cycle of an insect begins with an egg, it generally hatches outside its mother's "womb" into a larva or a nymph. For the juvenile insect, life is taken up with eating, growing, molting, and growing bigger until it is ready to become an adult. This process is referred to as metamorphosis.

Metamorphosis actually infers "change." The term is of Latin and Greek origins: meta means change and morphe means form. This process describes the series of changes through which an insect passes in its growth from the egg stage (some insects, such as aphids, may produce eggs and/or give birth to live young) through the immature stages (nymph, larva or pupa) to the adult stage.

Unlike us who have internal skeletons, insects have an exoskeleton, one that protects it from its environment. To grow bigger, an insect needs to shed its tough outer exoskeleton, or molt. When the insect is ready, the old exoskeleton cracks open and the insect slowly crawls out. Free of its old "skin," the insect stretches itself out, puffs itself up and dries out its new exoskeleton. While it waits for its exoskeleton to harden it is quite vulnerable.

Juvenile insects molt many times as they grow larger, often changing into quite different organisms by the adult stage. When it molts, it enters another stage that may or may not look different from the previous stage. These are called instars. There can be several larval or nymphal instars.

Depending upon the species, an insect's life stages are characterized by either complete or incomplete (simple or gradual) metamorphosis. Insects that undergo complete metamorphosis have four life stages: egg, larva, pupa and adult. The larva looks dramatically different to the adult insect, and must go through a pupal or transition stage before it develops into an adult.

Pupation occurs at the final molt. It is an apparent inactive stage during which the larva undergoes a most dramatic change. When it emerges from the pupa, it has become an adult. It has wings, fully functional reproductive parts and looks just like its parents.

Complete metamorphosis gives insects a significant survival advantage. The adults and larvae, being different, do not compete for the same food sources and have different predators.

Complete metamorphosis occurs in 85 percent of known insect species. That includes all of the major successful insect groups such as beetles, wasps, bees, ants, flies, moths and butterflies. Other insect species that undergo complete metamorphosis include fleas, alderflies, lacewings, scorpion-flies and caddisflies.

Insects that undergo incomplete metamorphosis have three life stages: egg, nymph and adult. These insect begin life as a wingless nymph. In many cases it looks like a miniature adult. With each successive molt, the insect increases in size and looks more and more like an adult. On a flying insect, wings will gradually appear. After the last molt the insect is fully adult, able to use its wings and reproduce.

Insect species that undergo incomplete metamorphosis include silverfish, mayflies, dragonflies, damselflies, stoneflies, cockroaches, termites, praying mantids, earwigs, grasshoppers, stick-insects, booklice, parasitic lice, true bugs and thrips.

Sometimes I wish I had an exoskeleton like an insect. Maybe that would prevent me from eating too much. But only if I couldn't molt. I can't imagine what that would be like!

Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.

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Surface Creek
Jim Leser, What's Bugging You
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