are usually found on the throat and the base of the legs and abdomen
of crablike legs with terminal tarsi with 2 tarsal claws
pairs of wing pads
460 species known to inhabit North American, colour is varied, however
shades of yellow, orange, green, brown and black are the most common.
Quite often stoneflies are 2 toned.
stoneflies look much the same as the nymphs with the following differences:
are folded flat over the back and often extend 10 to 20% past the tip
of the abdomen
stoneflies skim the surface of the stream, dipping their abdomens in
the water and releasing their eggs. Others will actually crawl to the
bottom of the stream and then release their eggs on submerged objects.
Stoneflies are very clumsy fliers and during the egg releasing procedure
will cause quite a fluttering and splashing on the water surface which
immediately attracts the attention of hungry fish especially steelhead.
into a nymph stage which, depending on the species, can last up to 3
years requiring up to 25 molts to develop completely.
do not go through a pupa stage and is therefore considered an incomplete
will crawl out of the stream onto a stone, tree branch or log and remain
long enough to dry and split it's nymphal case. The adults will emerge
from the exoskeleton, looking very much like nymphs with wings added
and will then fly or climb into the nearby trees. Following the emergence
the adults will mate (males attract the females by drumming their abdomens
on a tree branch) and then the females will start the lifecycle over
again by depositing her eggs back into the stream. Depending on the
species, stonefly adults may live for several weeks.
will feed on organic and vegetable matter found in the stream substrate.
are carnivorus, feeding on mayfly nymphs and other insect larva.
nymphs require well oxygenated water so are consequently found in rivers
and streams amongst the rocks and bottom debris, a few species can also
be found in the rocky shoals of cold lakes.
are available to fish year round
are very poor swimmers and prefer to crawl amongst the rocks on the
river bottom using their clawed crablike legs
often they will loose their footing and will drift helplessly down current,
thereby being at the mercy of fish
often target nymphs as they attempt to crawl out of the water during
case the fisherman must imitate this action by keeping the fly near
the bottom, this can be achieved by casting upstream or up and across
and letting your fly sink and tumble with the current along the stream
female stoneflies are also highly prized by fish, they clumsily make
contact with the water to deposit their eggs. This is an extremely important
time for the dry fly fisherman. Imitating the fluttering, splashing
movement of a female stonefly on the water surface will often provoke
a violent response from trout or steelhead.
nymphs and juvenile steelhead share the same habitat. Stoneflies, because
of their size provide much of the steelhead's food requirements. This
relationship of stonefly nymph and juvenile steelhead is called "juvenile
habitat imprint" and is very important when trying to find the holding
areas of large adult steelhead returning from the ocean to their home
streams for spawning. More importantly to the dry fly fisherman is the
relationship between the juvenile steelhead and the adult female stonefly.
Unlike caddis flies, adult egg laying stoneflies do not swarm. Therefore,
a single egg laying female upon the water surface will provoke a very
competitive feeding response from many fish including the juvenile steelhead.
This relationship of the single egg laying stonefly and the feeding
response of the juvenile steelhead is called "the single fly juvenile
feeding imprint" and explains why a non-feeding upward migrating adult
steelhead will take a dry fly. Quite simply, the fluttering dryfly will
trigger the "juvenile feeding imprint" in the adult and it will strike
the fly. This behavior is very important to the fisherman, because when
steelhead enter the river from the ocean to spawn there is usually no
adult stonefly activity. Adult stoneflies usually die during the middle
of late summer.