FEBRUARY
2001

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

02-24-01

Case Makers of the Insect World

We're all familiar with containers called cases. There are cases in which to store things: eyeglass cases and jewelry cases, for instance. Briefcases and suitcases are designed to carry things.

There are cases that cover the pillows on our beds. We buy individually bottled items, such as beer, soft drinks or even ketchup, in quantities by the case. Our guns and musical instruments are stored and transported in cases.

Most of us have books arranged in bookcases. Stores and museums use cases of all sorts to display and protect items.

Cases are also used by insects to provide protection, generally in the immature stage. Insects that employ such a strategy are called case makers. And if they drag the case around with them, like we do suitcases, they are appropriately called case bearers.

So how do insects acquire their cases? They don't purchase cases at the local outlet store; they make them. Case-making insects produce silk. They use the silk to tie materials together into the form of a tube. The cases are usually cylindrical with just enough room to house the body of the insect.

The immatures of midges, mosquito-like insects, live in water and produce a small silken tube to which particles of sand or plant matter are fastened.

Black flies, those pesky biting flies, also produce a silken case where they form a pupa and turn into the adult fly. Black fly cases are found attached to rocks in swift streams. Sometimes these golden-colored cases are so numerous that the rocks appear to be covered with a golden silk blanket.

Some insects that live in meal and flour also produce tubes. The Indian meal-moth and the Mediterranean flour moth use strands of silk to join particles of meal or flour. This is the silk mass that we sometimes encounter when we open a container of meal or flour that is infested with these insects.

Another home pest makes a case and is appropriately named. The case-making clothes moth spins a case using silk and the fragments of the material upon which it feeds. The moth adds insult to injury by enlarging its case as it grows.

The evergreen tree pests, which we know as bagworms, are also case makers. The bag is a case. The larvae of the bagworm, which in the adult stage is a moth, uses pieces of bark, leaves or needles to construct this protective shelter. In addition to providing a home for the larvae, the bag is also home to the wingless female and the eggs that she leaves behind. That is why it helps to control this insect pest by removing the bags from the trees during the winter and destroying them. You get rid of next year's worms that way.

The lily-leaf caterpillar creates an unusual case by chewing two pieces of leaf material. The two pieces are then fastened together to form a sleeping-bag type of structure in which the larvae lives. As it grows, it just cuts two new pieces and sews them together as a seamstress human mother might do to create a new jacket for a growing youngster.

Casemaking has been developed to a high degree by larvae of the caddisflies. These aquatic insects build their homes out of any type of available material. Caddisfly cases are made of small stones, sand, bits of vegetation and even small snail shells.

Some creative jewelry makers have put the caddisfly casemakers to work creating works of art. The caddisfly larvae are placed in an aquarium with only one kind of building material, say sand or precious stones. The larvae build their cases. When the cases are abandoned, the jewelers then create jewelry using the insect-made cases.

Wow! Diamond-studded caddisfly-case earrings-there's a fashion item that is sure to raise eyebrows. After all, how many people do you know who own an abandoned insect case as jewelry?

 

Writer: Tom Turpin
Editor: Olivia Maddox