Blackfly (Simulid) larvae thriving in what they need, a well-oxygenated fast flowing stream, the River Nar. Ecosystem engineers, their fecal pellets provide nutrients to such #chalkstreams, the adult flies being favoured trout food (emulated by anglers). #riverflies #rivers #invert #wildlife 6/9

Besides Duck Mussels (Anodonta anatina), Lymnaea stagnaris snails & plentiful caddis fly larvae eg Potamophylax?, some surfaces of River Nar above #Narborough were rendered hairy by a layer of Black Fly (Simulid) larvae. #Riverflies #chalkstreams #Norfolk #MolluscMonday #snails #invert #nature 5/9

Looking back at 2025 with @riverflies.bsky.social: a year of collaboration, conferences & #citizenscience.

12 months of amazing action for #riverflies & #freshwaters... geographical reach is now larger than ever, with 700+ rivers being monitored by 2000+ volunteers!💙

www.fba.org.uk/fba-voice/th...

Image 1 featured in the Riverfly Partnership 2026 Calendar by Paul Fraser

Image 2 featured in the Riverfly Partnership 2026 Calendar by Andrew Gibson

Image 3 featured in the Riverfly Partnership 2026 Calendar by David Warriner

Image 4 featured in the Riverfly Partnership 2026 Calendar by Chris Avery

If you, like us, are in awe of #riverflies, check out the fantastic @riverflies.bsky.social 2026 Calendar! Each month is a celebration of the #freshwater species and habitats all the amazing riverfly #volunteers work to protect. 💙

Get your mandibles on a copy today!
www.fba.org.uk/shop/p/river...

photo by @billsutherland.bsky.social

photo by @billsutherland.bsky.social

Given the abundance of Trout & Grayling in this reach of the River Test catchment, was surprised not to see more invertebrates. The caddisfly larvae were different from those I see in East Anglian chalk #rivers. Plenty of Signal Crayfish holes in the bank. Water already only 7°C. #Riverflies 3/7

Hello freshwater friends and fellow lovers of leeches... our October edition of FBA Voice is out now! This month includes features on #Riverkin #Riverflies #FreshwaterPearlMussels #FBAHistory #CitizenScience #MedicinalLeech and more!

Check out the October FBA Voice here:
mailchi.mp/fba/welcome-...

📢 Big River Watch starts today!

Download the free app, spend 15 minutes by your local river, and complete the short survey to tell @theriverstrust.bsky.social what you see.

Get your survey in by the 25th of September! #BigRiverWatch.

#TheRiversTrust #river #nature #riverflies

Cohabiting with River Lowther's salmon parr were quite a few Stone Loach, out in open.
Under a stone, a Chabot Bullhead, more muted in colour than those I am used to in East Anglia. See caddisfly larvae stone igloos + another sort hanging off a rock.
V few Threespine Sticklebacks. #riverflies 9/20

To end 🧵on fab new #fish pass installed at Turf Lock Mildenhall to enable unimpeded passage of fish along River Lark, here's some fish enjoying pool formed beneath it. Roach here as well as Dace (always suckers for oxygen rich pools), Perch & Gudgeon, while #riverflies dance in the sunset. 17/17

Above the River Lark, #riverflies danced in evening sun. Below surface, freshwater sponges (Spongillidae) grow on underside of the stones in the new #fish pass, beneath which are a few caddisfly larvae, the case of this one adorned with a delicate Pea Cockle (Euglesa). #MolluscMonday #invert 13/17

Besides Brown Sedge, Potamophylax were the predominant caddisfly larvae in Cut-Off Channel at Wretton, incl. some we inadvertently brought home on the Steppe Bison bones.
Lots of bright red Hydrachnidae Water Mites & in the sandy shallows Water Boatmen (Corixini).
#Riverflies #invertebrate 16/21

Here you see in more detail how Zebra Mussels (Dreissena polymorpha) coat hard surfaces such as tree trunks & freshwater mussels eg Swollen River Mussel (Unio tumidus) (plus caddisfly larva on the Zebra!) & Duck Mussel (plus freshwater isopods Asellidae). #riverflies #invertebrates #Norfolk 14/21

Another fascinating aquatic invertebrate of the Cut-Off Channel is this larva of Bicolour Sedge Caddisfly (Triaenodes bicolor); it propels its exquisite case, made of a spiral of bright green plant material, through the water, by whirring its hairy back legs. #Riverflies #invertebrate #Norfolk 3/15

Love bizarre Bicolour Sedge Caddisfly larvae scooting about in little green cases. Below, trails criss-cross Cut-Off Channel bed made by Brown Sedge caddisfly larvae & Common River Snails.
See also Northern Caddisfly larvae eg Limnephilus flavicornis with case of shells. #riverflies #norfolk 22/25

Happy Insect Week!
🎣 Meet the Angler’s Curse up-wing fly.
The nickname comes from how their mass emergence leads to feeding frenzies for fish — this can cause difficulty for anglers who can't compete!
#InsectWeek #Riverflies #Freshwater #Mayfly #CitizenScience #AnglersCurse

Not many #riverflies in Sapiston River/Black Bourn below #Ixworth, though I did meet this Banded Demoiselle nymph.
There were a few colonies of Sessilida ciliates and some freshwater sponges (Spongillida) - lilac & green specimens right next to each other on the riverbed. #rivers #chalkstreams 6/10

In some places, the bed of Lode Dike/Stringside Stream was crawling with those hardy #riverflies, Brown Sedge Caddisfly larvae (Anabolia nervosa), defended from (absent) fish by the sticks they armour their cases with. #Chalkstreams #Norfolk #rivers 2/5

To end this🧵on Lode Dike/Stringside Stream, a glimpse of the joy that can come from floating down a clear-watered #chalkstream, over beds of Unbranched Bur-reed, #riverflies dancing over the surface, on a tranquil May evening, even if the river is sadly ailing. #Norfolk #rivers🌍 12/12

In Lode Dike/Stringside Stream, low diversity/density of Caddisfly larvae but a few northern caddisflies (Limnephilus) with cases of tiny shells & ?Potamophylax with stone mosaics. Swarms of little ?mayflys tho'.
The chalky bed rock hints how this #chalkstream SHOULD be. 🌍#rivers #riverflies
8/12

Plenty of what I guess are Potamophylax caddisfly larvae, cases made from mosaics of tiny stones, crawling around the bed of Lode Dike/Stringside Stream. Also Limnephilus flavicornis, with more extravagant cases fashioned from variety of snail & bivalve shells. #riverflies #rivers #Norfolk 8/10

Yet #riverflies are in this upper 750m of Stringside Stream: larvae of ubiquitous Brown Sedge (Anabolia nervosa) bearing sticks, & other Northern Caddisfly (Limnephilus), case of tiny shells + Banded Demoiselle nymphs, some on chalk lump, horribly coated in weird silt of this sick #Chalkstream. 4/8

Really shocking how few #riverflies I saw in #RiverLark at #Mildenhall. Only noticed this Banded Demoiselle nymph, tho' there were #Odonata on the wing.
Quite a few Duck Mussels (Anodonta anatina) & below fish pass, a mussel sporting Frogspawn Algae (Batrachospermaceae)! #MolluscMonday #Algae #9/12

The complete lack of visibility in Fritton Lake due to dense green algae (apparently was clear a few weeks ago), meant I focussed on the insects floundering on the water surface. Delighted to spot an Alder Fly (Sialis) as well as masses of Non-biting Midges (Chrinomids) & a Cranefly. #riverflies 2/3

Here's a selection of Limnephilidae Northern Caddisfly larvae on the bed of this tributary of Stringside/Lode Dike #chalkstream. Most of these have used snippets of reed stem, with the ones lower right, mosaics of stones. #Riverflies #Trichoptera #caddisfly #chalkstreams #norfolk #invertefest 8/14

The #chalkstream / ditch bed was crawling in places in Brown Sedge (Anabolia nervosa) Caddisfly larvae with their anti-fish stick armour. Also some Limnephilus flavicornis, their exquisite cases made of tiny shells. More caddisfly larvae among the chalk gravel at a culvert outflow. #riverflies 7/14

More caddisfly larvae hanging out by a Bullhead: Armour-ballast Caddisfly (Goeridae) with keel of larger stones & Northern Caddisfly (Limnephilidae). Also lots space invader-like Ecdyonurus Mayfly larvae under stones & plenty Wandering Snails (Ampullaceana balthica). #Riverflies #MolluscMonday 7/13

Plenty Caddisfly (Tricoptera) larvae in River Pont eg stony domes of Little Black (Glossosomatidae), sticks incorporated by Brown Sedge (Anabolia nervosa) to avoid consumption by trout, mosaic horn of Silver Sedge (Odontocerum albicornea)? & stony tubes of Potamophylax Northern CF. #Riverflies 6/13

Plenty fish food in Old Carr Stream, in form of Caddisfly (Trichoptera) larvae with a dazzling array of cases, including high densities of the little stone igloos of Little Black Caddisfly (Glossosomatidae) larvae. #riverflies #chalkstreams #Norfolk #trichoptera #aquaticinsects #aquaticlife 12/16

For Microscope Monday 🔬 we present some magnificent magnification of the stunning #stonefly.

#Plecoptera are a very important component of British and Irish #freshwaters, most common in fast-flowing, clean rivers & streams.

Keen to improve your knowledge of #riverflies?
www.fba.org.uk/courses-2025

Thanks again for this shout out! We had lots of website visit and enquiries, now prospective volunteers have been put in touch with their local groups for spring training. 😀
#citizenscience #invertebrates #riverflies #empoweringcommunities