SEPTEMBER
2011

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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09-22-11

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Golden Pupae Belong to Butterflies


The pupa is a stage in the lifecycle of those species of insects that exhibit complete metamorphosis. Such insects begin life as an egg that upon hatching becomes a form called the larva.

Larvae have other names, such as caterpillars in butterflies and moths, grubs in bees and beetles, or maggots in flies. Larvae are often called eating machines because food consumption is their game. Once the larva has completed feeding it changes into a form called the pupa.

The pupa is sometimes called the resting stage in the insect lifecycle. That is because most pupae are not as active as either their previous larval form or their succeeding adult form. At least outwardly they are not as active as they were or are about to be. On the inside, though, the pupa is very active, undergoing miraculous changes in structure. And generally the pupa can wiggle around a little.

Ancient people poorly understood this change in form, or metamorphosis. They didn't know how it worked or which larvae became which adults, or even that the larvae became adult insects. So the Latin word larva - meaning mask - was used for immature insects to represent the idea that what it was and what it would become were hidden.

In similar fashion the biological attributes of insect pupae were also poorly understood. However, the general shape and structure of insect pupae apparently reminded people in those long-ago times of a type of children's toy. Today we call such toys dolls. So pupa, the Latin word for doll, became the name for this insect stage. This is also the basis for the word puppet.

So what do these dolls of the insect world look like? Well according to the way pupae appear, scientists divide them into three types. In one type the pupa is covered by a hardened version of the last larval exoskeleton. In the other two types the adult appendages are visible. Of these some have appendages that are free from the body while others have appendages that appear glued to the body. This last type of pupa is the one that most likely inspired the comparison to ancient, wood-carved dolls where appendages were carved as part of the doll or painted on the surface.

Most butterflies and moths have pupae where the appendages appear glued to the body. But in some instances, primarily the moths, the pupa is covered by a silken cocoon and is not visible. Probably the best-known example of such an insect is the silkworm, the cocoon of which provides the fiber for the silk industry.

Not all moths have covered cocoons, and one is a well-known pest of our gardens - the tomato hornworm. When this hornworm caterpillar completes feeding it crawls from the tomato plant and burrows into the soil where it creates a pupation cell. In this case, the proboscis of the moth-to-be extends from the front end of the pupa, forming what writer Floyd Bralliar once described as a handle in his book, "Knowing Insects Through Stories." Indeed that structure is a good handle, which can be used to pick up a hornworm pupa.

Butterfly pupae are all the type with appendages adhering to the body. Butterfly pupae have the special name chrysalis, a word based on the Greek root "chrys" that means gold. It is an appropriate name because several common butterflies, including the Monarch, produce a chrysalis with gold flecks.

One of the most striking of the golden butterfly chrysalids is that of the variegated fritillary. The fritillaries are brownish-colored butterflies with black wing markings that are often seen flying rapidly over summertime meadows. The variegated fritillary feeds on plants such as violets. When it is ready to pupate the caterpillar attaches its rear end to a solid surface such as a plant stem and changes form. It produces a striking pupation case that is a credit to the historical basis for the name chrysalis - gold!

 

Writer: Tom Turpin
Editor: Olivia Maddox