Yeah artc's are jumpers mine which was about 7 inches jumped out of a half inch crack believe it or not where my filter hung on to and the next morning an ant trail led me to him. So better cover up every little crack you got on your tank.
Must be aquaclears, i find my syno's in mine everyone in a while. I let the water level down a bit to keep them from getting in there anymore. I feared the might get caught in the mesh bag. You might want to do the same.