The terrorists' letter arrived at the mayor of Los Angeles's office on Nov. 30, 1989.

A group calling itself "the Breeders" claimed to have released the Mediterranean fruit fly in Los Angeles and Orange counties, and threatened to expand their attack to the San Joaquin Valley, an important center of Californian agriculture.

With perverse logic, they said that unless the state government stopped using pesticides, they would assure a cataclysmic infestation that would lead to the quarantining of California produce, costing 132,000 jobs and $13.4 billion in lost trade.

The infestation was real enough. It was ended by heavy spraying.

It is still not known if ecoterrorists were behind it, but the panic it engendered shows that "the Breeders" were flirting with a powerful weapon.

The history and future of insects as weapons are explored in my new book, "Six-Legged Soldiers." As an entomologist, I was initially interested in how human beings have conscripted insects and twisted science for use in war, terrorism and torture.

It soon became apparent that the weaponization of insects was not some quirky military footnote but a recurring theme in human strife, and quite possibly the next chapter in modern conflicts.

Insects are one of the cheapest and most destructive weapons available to terrorists today, and one of the most widely ignored: They are easy to sneak across borders, reproduce quickly and can spread disease and destroy crops with devastating speed.

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