The ship's cat has been a common feature on many trading, exploration, and naval ships, and dates back to ancient times. Cats have been carried on ships for many reasons, the most important being to catch mice and rats. These rodents aboard a ship can cause damage to ropes, woodwork and eventually as technology progressed, electrical wiring. Also, rodents threatened the stores the ship carried. Rodents may devour the foodstuff carried to feed the crew, and could cause economic damage if the ship was carrying grain or similar substances as part of its cargo. Rats and mice were also sources of disease, which is dangerous for ships that are at sea for long periods of time. For example, rat fleas are carriers of plague and it is believed rats on ships were one of the main spreaders of the Black Death.Cats naturally attack and kill these rodents. The natural ability of cats to adapt to new surroundings made them suitable for service on a ship. They also offered companionship and a sense of home, security and camaraderie to sailors who could be away from home for long periods, especially in times of war.