Unwanted guests

Swallows have been living alongside man for a long time now, making their nests beneath man's eves. But not all of our urban companions are so welcome. Rats and cockroaches now share our food, while many insects feast on the cellulose that is found in the paper and books all around us. Also, grubs chew the sheep hair with which clothes are made. Brown rats originated in Asia and spread to Europe around 300 years ago. Today rats are found in every large city in the world and will eat almost anything. They gnaw electric cables, thereby causing short circuits and fires, and they contaminate food and spread disease. Humans have to manage their environment, but are making a very poor job of it so far.

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