3 days ago I lift up my large rock in one of my shrimp tanks and I discovered there are 4 bugs that looks exactly like a House Centipede: http://en.wikipedia.org/wiki/Scutigera_coleoptrata

It is about a inch size and pure white and the head is quite small and I can't see how the face looks like. It has 12 legs and with 2 long tails like the antenna. Usually when I lift the rock, they will stay stationary and once they move, it is lightening speed and very good at burrow under the rock. I tried Googled but there is no aquatic insect looks like this and from what I know, House Centipede should be able to survive submerge for too long.

Today, I decided to eradicate them. I lifted up all my rocks and only found one. I tried to stir up the gravel but can't find the rest.

Does anyone know what is it?