i have just setup a new tank, cycling completed a week ago and I have started to add fish, everything is going well. I whent to clean out my filters today and found a strange creature buried head first in the carbon filter. If I have done this right then there should be some pics of it. one as I found it an one sitting in a jug.
I'm guessing this is some sort of larvae, does any one know what it is and if they are harmful?
yes it's some kind of larvae. Harmful or not is depending on what type of fish are you keeping. Fish such as tetra species, those larvae could be a problem but bigger fish such as cichlids, those become food.
They've managed to survive and become this big means you should get rid of it
I have three Adult Glowlight Tetra one adult platy and two"teenage" platy. they have only been in the tank a week, I guess the larvae got in there via the plants I put in. The tank cycled for about 6 weeks, so it would have had all of the tank to it's self.
If these are likely to be harmful are there likely to be more and is there anything I can do, other than keeping an eye out for them?
It's not really something you should concern about cause' unless you have fry or trying to breed your fish. There won't be any damages. (or keeping small species)
Those are usually to be introduced to the tank along with plants and you can't sure if the plants are egg-free. Best way is spend a little time enjoying your fish and also look out for anything weird. They're not pest and won't breed, also they will die off if there aren't any food so not a big deal.
However keep in mind that if you spot anything unknown, best thing to do is take it out first for the fish's safety :P
Oh heavens to betsy, I hate it when people post photos of those horrible wee things, they give me the creeps no end. It's disgusting, that's what it is. The best way to deal it would be a MASSIVE controlled explosion.