MAY
2010

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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05-27-10

Download the audio of On Six Legs: MP3, WMV.

Extreme Makeovers Commonplace in Insect World


In the world of reality TV, one show featured humans getting a physical makeover. Teams of plastic surgeons, cosmetic dentists, hair stylists and personal trainers changed the way a person looked. Supposedly, as a result of the makeover, the lives and destinies of the participants also changed. No one really knows if the recipients of the extreme makeover became modern Cinderella stories or not. What we do know is that this TV show suffered from low ratings and went off the air in 2007, after its fourth season.

In the insect world extreme makeovers are common and have been part and parcel of insect biology for millions of years. Such makeovers are incorporated in a process known as metamorphosis. This process has been touted as one of the reasons that insects are such successful organisms.

To many people the most familiar type of insect metamorphosis involves four life stages - egg, larva, pupa and adult. During this type of a metamorphosis the insect changes completely in form. For example, a caterpillar transforms into a butterfly, or a maggot turns into a fly.

It is in the pupa where an extreme biological makeover occurs. Tissues and chemicals from the larva are torn down and reconfigured into a totally different adult form; thus, metamorphosis literally means a change in form.

The term pupa has a Latin origin where the word was used for a baby or doll. The Swedish naturalist Linnaeus proposed the use of the word for this insect stage and was probably inspired by the appearance of the pupa of a butterfly. Such a pupa resembles a baby wrapped in a blanket where the general body shape and appendages, such as arms and legs, can be discerned. Many ancient dolls were carved in just such a manner with the arms and legs affixed to the body.

Not all insect pupae look alike. Sometimes the appendages, such as wings, antennae, legs and mouthparts are not free and are appressed to the body. This is how it is with pupae of butterflies.

In other insects the appendages of the body are free, as is the case in many beetles. In some insect pupae, such as the house fly, the appendages are not visible at all.

The amount of movement displayed is also used to group insect pupae.

All insect pupae exhibit some movement, but in most the movement is limited to what most people would call wiggling around. Some of the hummingbird moths have pupae that use the abdomen to work their way from the soil before the moth emerges.

The most active insect pupae belong to mosquitoes and midges. Both of these types of insects are aquatic in the immature stage, as are their pupae. These pupae can actually swim by moving the rear end of their bodies. Mosquito pupae are called tumblers because of the motion they exhibit in the water.

Scientists sometimes classify pupae according to the amount of covering. For instance, some pupae do not have a protective cover. Such pupae are appropriately termed naked. Naked pupae are often found in the soil or wood. However, all butterflies have naked pupae, and these are often found in the open, hanging from a surface such as the leaf of a plant. Butterfly pupae are given the name chrysalis, a name based on the Greek word for gold because a number of butterfly pupae have observable gold flecks.

Sometimes insect pupae are covered by silk. The silk is produced by the immature insects, including those of the majority of moths and few species of beetles, flies, fleas and wasps. Such silken coverings of pupae are called cocoons. The most famous cocoon maker is the silkworm Bombyx mori, an insect that uses 1,000 feet of silk to wrap the pupa.

So in the insect world the makeover that occurs in the pupa is of an extreme nature. The changes allow the insect to go from having chewing mouthparts to having a siphon for sipping nectar, as is the case in butterflies and moths. In flies, the change is from a maggot with no legs to an adult with six legs. But most remarkable of all is to go from a wingless immature landlubber to an adult with two or four wings and the ability to fly. That is an extreme makeover, and it isn't even a concoction for reality TV. It is just nature at its everyday best.

 

Writer: Tom Turpin
Editor: Olivia Maddox