I had a tank in storage years ago that became a nursery for breeding cockroaches. When I went to get the tank out of storage, there were literally thousands of roaches (from babies to adults) scurrying around everywhere. I had left the damp, dirty gravel in it and they found it irresistible. The tank (along with everything else that shared the storage space) spent the night locked in the back of a U Haul truck after I set off 3 bug bombs in there. EVERYTHING was dead the next day. lol