Trench rats were rats that crawled through trenches and spread diseases through. These trench rats grew to the size of cats feeding on dead or even wounded men that couldn't defend themselves eating them alive. Soldiers said in their diary that they even took food out of the sleeping men and said that they were enormous in size. One pair of rats could produce over 880 rats in one year . And another account of a soldiers diary said that he saw a guy with his skull showing with no flesh.
This is a picture of a photo shopped skull with flesh but I believe that this is what it would look like if you got ate by rats.
Soldiers could hear them eating the leftover food in no mans land and eating the dead men's flesh. They crawled all over the soldiers while sleeping. And they showed up mostly along the western front with millions in total. They started shooting at them but they ended up not being allowed because it was a waste of ammo. Since they were already running out of ammo it pretty much got banned.
Rats being hung to show their size.
Today I believe that some rats show up on the battlefield in like Iraq other than that its mostly house rats and mice. Or in the dead body trying to get a meal. they have mostly disappeared today because our ways of wars have changed like cleaning up the bodies and not leaving food on the field. We also don't have a big problem with leaving trash on the land that's another reason why we don't have rats.
Dead soilders on a ww1 battlefield
During the war the dead soldiers would lay there until the generals told the soldiers to pick up their brothers and bury them or cover them up and take the left over supplies. If that didn't happen left over foods would be eaten by the rats and the dead bodies would also be eaten. Today in war we don't kill by the masses and if we do we clean the bodies up right away and try and save them even though there wasn't any recent wars right now. But we would bring them back to america to be buried.
bibliography http://spartacus-educational.com/FWWrats.htm http://www.firstworldwar.com/atoz/rats.htm