The Rhyacophila - free swimming larva of a green sedge

What are Rhyacophila ?

An important nymh for fly fishermen the Rhyacophila is the free swimming larva of a green sedge and is best fished close to the riverbed. Large, usually green, and always plump, and they don't build cases or nets. They roam freely about the fast water and they often drift loose, where they are a good food for trout. Many of these larvae have no gills at all and rely on absorbing oxygen from the water through their skin. Only cold water and fast flows can meet these needs, so Rhyacophila caddis flies love the same habitat as trout. The larvae may rappel between the rocks on a line of brown silk they secrete. This can be imitated by colouring the last foot or so of one's leader with a brown marker pen. Fly tying a deadly Ryhacophila imitation is simple with Semperfli's Straggle String

Gary LaFontaine wrote some good tips in his book Caddis Flies about fishing appropriate flies for the water you're covering: “A good imitation of a Rhyacophila larva is going to catch a lot of trout in swift, bouncing stretches of stream. The same fly is going to do poorly in slow areas of the same stream. A fly fisherman can avoid wasting time in the wrong sections of a stream by working leap-frog fashion instead of in a straight line. If he is using an imitation of a fast-water insect he should fish only the swift, broken currents, skipping past the slower current areas. Likewise, if he is using an imitation of a slow-water insect he should only cover the quieter pools and flats.” This is an idea fly in late autumn and in early spring as the Grayling are into the faster riffles where Rhyacophila are prolific.

Sandys Deadly Rhyacophila Nymph








Sandy’s Straggle String Rhyacophila

Tying The Deadly Sandy’s Straggle String Rhyacophila – Ideal autumn and spring fly for use on swift rocky water. This is an extremely simple fly to tie but extraordinarily effective imitation of the Rhyacophila. It uses Semperfli Straggle String for the body which has UV strands which look like legs moving. Added to the colour of the Straggle String SF7250FL matching the Rhyacophila perfectly, used on fast bouncing stretches of water this is a deadly fly.


  • Straggle String SF7250FL (Fluorescent Green) – Body
  • Straggle String SF0050 (Black) – Thorax
  • Kamasan B100 grub hook
  • Semperfli Nano Silk thread (black).

Step By Step

  • Tie on Nano silk running the thread down to the shank on the bend
  • Tie in Straggle String SF7250 and run the Nano Silk back along the hook shank to 5mm from the head
  • Using touching turns wind the SF7250 to the Nano Silk, tie off and cut the SF7250.
  • Tie in the Straggle String SF0050
  • Wind the Nano Silk to the eye then using touching turns wind the SF0050 to the eye
  • Whip finish
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