The Crawler is the boss for the Scream Train level of The House of the Dead: Overkill. It is the fourth boss of the game. While having a distinctly insect-like appearance, it is obvious that it was made from a human base. It has developed double joints on each limb, allowing it to perform several acrobatic feats. Its hands have fused into two large talons, capable of slicing through steel. However, these talons are also its weakpoints, possibly housing sensitive nerve endings.
In Creeping Flesh (Extended Cut) the Crawler is seen in a big pipe, apparently it was loose and ate some cows in the slaughter house. At several points throughout the level, Crawler is seen running and attacking from above the train.
Before the actual boss battle, at one point Crawler rips off the roof of a train car and you must fight. After a few shots to his weakpoints, he is temporarily blown away.
First, Crawler will attack by hanging on to the sides of the train and attempt to slash at you. To stop him, you must shoot his attacking claw. This will cause him to momentarily fall off the train.
After this is repeated enough times, Crawler will jump over G and Washington onto the train. At this point, you must shoot Crawler in the face.
After the Battle
After Crawler is defeated, he falls in front of the moving train as G and Washington watch, to which Washington responds by saying it's "icky" and reveals his dislike towards bugs.