[anniec]

Thank you very much for the replies, and the useful link to all the caddis info. I hadn't realised there were so many kinds, having only seen ones in flowing water that make cases out of gritty debris. The pond in question has been through a lot of problems over the past few years, at one point becoming a stinking, lifeless mess, and I'm gradually getting it back to good health again. Last year it was like pea soup - although no longer foul-smelling and the wildlife liked it - but now the water is beginning to clear, helped by barley straw and the shade from the now-flourishing water lily, and it's good to be able to see the inhabitants again.
After such quick and informative responses to my first post you can expect lots more queries in future!