12/06/2026
Thank you to Nick Taylor for the footage & descriptions.
These are two different types of stonefly larvae. Again from the Gover Stream.
This stream contains far more stonefly larvae, of more different types, than any of our other sites. As with the flat-bodied mayfly larvae, they will not tolerate pollution, so we don’t find many in the main river and none below the sewage works.
Some of the chunky, patterned ones you can see are around 15mm long, whereas the slimmer, more delicate ones are only 8mm long.
Stonefly larvae start off as vegetarians, scraping algae off stones, but as they grow older they become carnivorous, eating mayfly larvae, fly larvae and even small ones of their own kind!
When they are big enough to turn into adult stoneflies, they will crawl out of the water and up a stem. Like dragonflies, their backs will split and the adult fly will pull itself out. They usually do this at night.
Note that this is different from most flies, for example your average bluebottle, which goes through 4 life stages: egg, larva(maggot) and pupa, then adult. Mayflies and stoneflies are more primitive and only have 3 life stages: egg, larva, adult.
This is because they are more primitive creatures, which evolved over 200 million years ago.
In fact, mayfly fossils have been found that date from the Carboniferous, 300 million years ago.
Obviously, their lifestyle works, cos they’re still here!