Riverfly Invertebrates guide - Number 3 the Flat Bodied Stone Clinger

Flat Bodied Stone Clinger

Riverfly coordinator, Fran Swan, continues her guide to the 8 key invertebrates.

The RLA Riverfly team monitor 7 sites on the river every month to detect and count these species. That site gets a score which is then updated onto the national Riverfly Partnership Cartographer.  Introducing #3 The Heptageniidae

We find quite a few of these feisty little alien looking Heptageniidae of varying sizes (from a few mm up to about 15 mm) depending on how many moults they have made and how close to adulthood they are. 

Their common catchy name is Flat Bodied Stone Clinger and they live up to that description very well. 

Sporting a teardrop flattened body held low down and steady in the fast moving water by six strong, splayed legs each with a tarsal hook at the end. The wide squashed head has two large eyes near the back to spot any predators lurking above. 

They’re dark, often with dappled patterning giving good camouflage in the rippling water. 

The gills project from the side of the body like fluttering, feather dusters directing mini water currents with more oxygen into the crevice they call ‘home’. In some Heptageniidae, the front gills can even transform into suction discs aiding attachment to rocks. 

Any more survival tricks under that exoskeleton?

Three long elegant slender tails project out from the abdomen, like guy ropes to help balance and secure the larva in a strong current. 

These Stone Clingers hang out at the bottom of the river and are ideally suited to squeezing in crevices between rocks for protection and streamlined for fast water flow.  Scraping algae off the rocks, they don’t need to hunt for food and the moving gills bring in more tasty detritus. 

So a great checklist of adaptations for this aquatic larva of another ancient mayfly species. 

When their larval moulting days are over and it’s time for their short time as an adult, they move into slower water and emerge from the larval case, floating down the river drying their wings and when ready for action, fly off to mate.  

(See the Mayfly Ephemeroptera bio  if you’d like a reminder of their antics).  If anyone knows any more information about the physiology or behaviour of these critters, please get in touch - I’m just an enthusiastic amateur and would welcome any input.

This baby FBS clinger has got many moults ahead of it!

Brilliant macro shot below taken by Paul Fraser (ex Freshwater Biologist for the Clyde River Foundation and generously given photo permission here. Thanks Paul)

Instagram @pauls_macro_world