Creeper

The Creeper is essentially an enormous insect which looks like a cross between a tarantula and a Cockroach. They have a tough shell on their backs and a soft but skeletal underbelly. They attack in swarms, scurrying along the ground and attempt to bring down their prey by nipping at their feet. While these creatures are not very harmful by themselves, the fact that they are always grouped together and very fast makes them a massive inconvenience and annoyance.

While they do have fairly a strong carapace, they cannot withstand a standard shoe - in all of their appearances they can be stomped on and squished like any insect might.

There seems to be a few different variants of the creeper, as when Harry Mason encountered them in Silent Hill, they were relatively large and aggressive. However when James Sunderland visited Silent Hill some time later, they appeared smaller and more passive - but there were many, many more of them which may mean that they evolve extremely quickly.

Finally, in the Silent Hill film adaptation, the creepers are the creatures which accompany Pyramid Head and instead have strange human-esque heads above their soft underbellies and simply seem to follow him wherever he goes.

In terms of their symbolism, they simply represent Alessa Gillespie's severe dislike of insects. Plus, they represent darkness and decay as creatures like cockroaches thrive in conditions that human beings detest.