u may not realise it blueyak but u have more than a few if they have been in there for more than a month. they usually only come out at night so u dont see them very often. they eat leftover food and dead plant matter. and they spin around in the substrate releasing all the built up gas pocket and mix the sand. they are great in planted tanks with a sand bed like eco becasue they dont eat live plants and u practically never see them.