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Insect Life Cycles

Introduction:

Butterflies, moths, and beetles undergo complete metamorphosis which has four stages--egg (ova,) caterpillar (larva,) chrysalis (pupa,) and imago (adult.)  Dragonflies bypass the pupal stage and undergo incomplete metamorphosis.  Grasshoppers and crickets on the other hand do not undergo metamorphosis at all.  Young grasshoppers hatch from an egg and go through several instars of feeding/moulting until they eventually become adults capable of flying.

Butterflies and Moths:

Butterflies and moths go through a four-phased life cycle called complete metamorphosis or "metamorphosis."  (Contrast that to the life cycle of a dragonfly which has three stages and is called incomplete metamorphosis.) 

The first stage of complete metamorphosis occurs when an adult female butterfly lays an egg or "ova" on the specific hostplant for that species.  After the egg is laid, it takes, on average, five days for the ova to hatch.  The newly hatched hungry caterpillar is termed a first instar because it has not yet moulted its skin.  When a first instar consumes enough foodplant that its skin is too tight to support further growth, the caterpillar becomes dormant for a day or so, and then sheds its skin revealing a larger head and new skin capable of sustaining further growth.  This caterpillar is now a second instar.  

Butterfly larvae repeat this pattern of feeding and moulting until the mature fifth instar caterpillar sheds its skin one last time to form a chrysalis or pupa.  (Note:  The term "cocoon" is a chrysalis or pupa with an additional outer shell of protection spun by a moth larva prior to pupation and only applies to moths; not butterflies.)  Some butterfly pupae will emerge from their chrysalis after 1-2 weeks.  Others wait until the next year to emerge because their larval hostplant cannot sustain another flight during the year in question.  When the fully grown butterfly emerges from the chrysalis, the cycle repeats itself.  

Adult butterflies no longer "feed" as their caterpillars did.  They do not have chewing mouthparts to ingest plants.  Instead, in order to sustain themselves, they have a coiled tubular straw or "proboscis" with which they obtain only liquid nutrients from flowers, streams, and sometimes animal dung.  Adult butterflies and moths do not grow.  They will die the same size they were when they emerged from their chrysalis.

Beetles:

Beetles, like butterflies and moths, also undergo complete metamorphosis.  However, unlike lepidoptera (butterflies and moths) beetle larvae are not called caterpillars.  They're just called larvae.  Below is the life cycle of the Cottonwood leaf beetle.

	Overwintering adult beetles emerge from bark and leaf litter in the spring as buds on host plants begin to open. The beetles mate and lay clusters of 25 or more yellow, oval-shaped eggs on the underside of leaves.
	After the eggs hatch, the small black larvae begin to feed by skeletonizing the leaves. The larvae feed gregariously during the early instars.
	As the larvae grow, they become lighter in color. The larvae may venture away from their siblings and feed separately. Older larvae consume all leaf tissue except for the main leaf veins and secrete a pungent substance if threatened. Larval development is completed in under two weeks.
	Mature larvae attach themselves upside-down to leaves and bark of their host or to weeds and grass underneath their host to pupate. The insect insect at the top left of the picture is a larva about to pupate.
	Adults emerge five to ten days after pupating.

Dragonflies:

Dragonflies undergo a three-stage life cycle called incomplete metamorphosis.  In fact, Dragonfly immatures, unlike butterflies and beetles are aquatic.  Female dragonflies fly directly over waterways dropping their eggs right in the water.  From the dragonfly egg, hatches what is called a nymph--the second stage in the dragonfly life cycle.  The nymph then goes through a series of stages--which can last for up to 4-5 years.  When a nymph sheds its skin for the last time, unlike lepidoptera, it does not form a chrysalis, it simply sheds its skin to reveal adult wings and the cycle repeats itself.  

Incomplete Metamorphosis

For a more detailed illustration of the Dragonfly Life Cycle, click here.

Grasshoppers and Crickets:

Unlike Lepidoptera (butterflies and moths,) Coleoptera (beetles,) or Odonata (dragonflies,) Grasshoppers and crickets do not undergo metamorphosis.  Females lay grasshopper eggs beneath the soil surface in pod-like structures that the female deposits from her abdomen. Each egg pod consists of 20 to 120 elongated eggs securely cemented together; the whole mass is somewhat eggshaped and covered with soil. A female grasshopper produces from eight to 25 egg masses. 

Some species of grasshoppers and crickets because of their large population size are considered serious agricultural pests.  The species of grasshoppers that cause major crop damage are the ones that overwinter in the egg stage, although a few other noneconomic species overwinter as nymphs.

In the Midwest, grasshopper eggs normally hatch in late April to early May. The peak hatch occurs about mid June and the hatch is usually nearing completion by late June. Cool and extremely dry springs may delay the hatch, allowing it to continue into July.

Young grasshoppers are referred to as nymphs. They are similar to adults in general appearance but are smaller and have wing pads instead of wings. There are usually five or six nymphal stages and the length of time from egg to adult is 40 to 60 days. Knowledge of grasshopper instar identification is useful because it gives a rough indication of how far the hatch has progressed.

Normally, once fourth and fifth instar grasshoppers are present, the hatch is winding down. More important, recognition of fifth instar hoppers indicates that the winged adult stage is soon to follow.  Wingpads of first to third instar hoppers are borne saddle-like over the thorax.  Wingpads of fourth and fifth instar hoppers are pointed backward over the abdomen and differ only in size. In the fourth instar they are relatively small and extend only to the first abdominal segment, while in the fifth instar they are large and extend past the second abdominal segment.

Once an the adult grasshopper hatches from the last nymphal stage, it has wings and is capable of mating and repeating the cycle for another year.  Winged adults are much more mobile than the nymphal stages.

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Utah Bug Club is sponsored by the Utah Lepidopterists' Society.

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