Richard Collins: Employing other species as security guards

Geese, sacred to Juno, were kept on the Capitoline Hill in ancient Rome. In 390BC, Gallic warriors tried to creep into the city under the cloak of darkness. Sleeping dogs failed to notice the danger but the geese did. They began cackling loudly, alerting the garrison and saving the ‘eternal’ city from disaster. The Romans never forgot their debt to the geese: one was carried in commemorative procession each year.

The ‘canary in the coal mine’ helped deal with another threat. Dangerous gases can be released when coal seams are opened. Carbon monoxide, invisible and odourless, is particularly lethal; it combines with the haemoglobin in the blood rendering it incapable of absorbing oxygen. Victims become drowsy comatose and die. Small birds need much more oxygen than we do, so canaries were taken down mineshafts. If noxious gases built up, the canary would die, alerting miners to the danger.