Strange plant bug?

please can someone help.. we recently purchased some new live plants..roughly 2 weeks ago, since then we’ve lost 2 fish but couldn’t understand why. Tonight we found this weird creature (presumably that’s come off the plants) however we haven’t a clue what it is.. managed to put it into a water bottle and all plants removed. It looks like a plant itself and a worm type thing comes out of it from both ends? Any ideas please? Thanks in advance

Is it a cocoon?

Yes I think it is.
We’ve just lost another fish.. in total 3 now

It looks like a caterpillar wrapped up in a leaf from the plants.. it also appears to be moving itself round with its head as if it was sucking to move?? Any ideas?

Google caddisfly. Most are apparently herbivorous