Trench rats were a huge problem during World War I. During this time, they infested every trench line in the war from the eastern to western fronts. The rats carried diseases that weakened and killed soldiers in the trenches, and some accounts say that trench rats attacked, killed and ate injured soldiers who could not defend themselves.
The rodents fed off of the dead and dying men in the no-man's-land between trench lines and would scavenge the food scraps left by soldiers in the trenches. Although shooting at rats was prohibited, as it wasted ammunition, rat hunting became a sport of sorts. Soldiers placed pieces of bacon on the end of their bayonets to draw rats close so that they could shoot shot or skewer them.
A pair of adult rats could breed between 800 and 900 young in the span of a year, leading to a proliferation of rats all over the battlefield. Some accounts suggest that trench rats grew as large as cats. Rats also carried lice in their fur, which were associated with trench fever. Although the disease was not fatal, it had the capacity to put a soldier out of action for up to three months.