Hints to Indentifying Stream Invertebrates

Bug Hints
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Links to more resources at the bottom of this page

Mayfly Mayfly


  • If a bug has three tails, it is a Mayfly, if it has two, look for further clues.
  • Gills are on abdomen, lower body
  • They dance (swim) in the water, often fold their tail like a scorpion
  • If there are lots, they are Mayflies (stoneflies die off more quickly)
  • 750 different kinds in total
mayfly Mayfly
  • This one is covered with an algae-like material (camouflage)
  • Ones with flat heads scrape algae off rocks for food
  • During fly stage, no longer has a mouth, just an egg laying machine.
  • Lives approx one year in water, 4 days as a fly
  • Adult has sail wings

Stonefly Stonefly


  • Segmented body. Like an ant
  • Two tails
  • Smooth body
  • Gills under armpits
  • They walk, donít swim
  • Have antennae
  • Very susceptible to pollution
  • Crawls out of head when becoming a fly.
  • Wings lie flat to body, one overlapping the other

Caddisfly Caddisfly


  • Makes its home from stones, twigs or organics
  • Ones with green body and red head bite. Free swimming (no home) predators, eat meat
  • Have two hooks on their tail to hold onto their casing (home)
  • Curl up when washed out of their home
  • Wings are like a pup tent

Water Beetle Water Beetle


  • Image to the right is riffle beetle in larva stage
  • Image to the left is riffle beetle as an adult
  • Stays aquatic

Aquatic Worm

Aquatic Worms

  • Come in a variety of colour
  • Look through a magnify glass to see if it has a head and legs, it may be a midge fly larva



  • The ones like the one in the photo, are predators. They suck water into their skin and then push it out to move. Like a squid.
  • Non predator looks the same except for the bulbous end


Water Snipe

  • Looks similar to the Cranefly larva, but has legs like a caterpillar

Water Mite

Water mites

  • Small
  • Tennis ball with legs
  • Comes in a variety of colours
  • Each colour is a different kind



  • Looks like a shrimp

Links added March 4, 2006, courtesy of Niall Williams