Science: Indigestible Wool

The British, whose Lord Chancellor sits on a woolsack and whose woollens clothe some of the world’s better-tailored figures, have been doing some basic thinking about clothes moths. Last week Textile Expert R. W. Moncrieff told how clothes moths (Tineola bisselliella) got their depraved craving for wool, and how modern chemists are persuading them to let the stuff alone.

In their wild state, says Moncrieff in the current issue of Discovery, moths did not eat wool. Their larvae ate dead animals on which the females deposited their small white eggs. But as soon as man started to make woolen clothes, many thousands of years ago, some moths began to change their feeding habits. With a good deal of difficulty, says Moncrieff, they learned to digest wool, have not yet completely adapted themselves to their unnatural diet. Researchers have proved that moth larvae grow faster when fed on fish meal or casein, and that unless they get vitamin B they never reach maturity. Vitamin B, plentiful in dirty clothes, is what a moth is after when he chews up a gravy spot.

Most moth repellents and mothproofing chemicals, says Moncrieff, are expensive, not very successful, and often wash out of the wool eventually. So wool-protecting chemists tried another, more subtle approach. Noting that even the best-adjusted moths can barely digest wool, they tried to make it completely indigestible.

First step was to study the chemical structure of wool, which is made up of long, thin molecules linked together crosswise, roughly as the side pieces of a long ladder are linked by the rungs. The chemists found that if they broke the cross links chemically, the wool was much easier for the moths to digest. The links, apparently, were the moths’ big problem. So the chemists reasoned that if the links were made stronger, the moths might not be able to digest the wool at all.

In natural wool, the long molecules are connected by “disulphide cross-linkages.” These the chemists replaced by “bis-thioether cross-linkages.” The artificial links are as strong mechanically as the natural ones, so the wool is as strong. The links are also stronger chemically, and the moths’ digestive juices cannot break them down. Moth larvae put on a diet of modified wool quickly starve to death, even though a few nutritious food stains are added. Moncrieff predicts that when all wool is modified in this way, clothes moths will have to return to their primitive diet.