Macroinvertebrate
Photographs and Descriptions
Developed by Big Sandy Resource Conservation and
Development Area
Courtesy of the U.S. Environmental Protection Agency,
the Kentucky Division of Water, and the Mountain
Association for Community Economic Development
WEF_Macroinvertibrates
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Aquatic Worms
Water Quality Indicators of Poor Water Quality (Group Three)
• Aquatic Worm
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They are either red, brown, or black
They have a circular, thin, segmented body
They can possibly be up to five inches
They often have short bristles or hairs that help them
move
(They are usually not visible to the human eye)
Measure 1 to 30 mm in length, but sometimes over 100
mm
Clear whitish to pink in color
Body consists of 7 to 500 segments
Segments often have bristles or hairs
Tolerant of low dissolved oxygen concentrations
Found in silty substrates and among debris or detritus in
ponds, lakes, streams and rivers
Dense populations of aquatic worms can often be
found in organically polluted rivers
Approximately 200 species in North America
WEF_Macroinvertibrates
Aquatic Earthworm
Aquatic Earthworm
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Leeches
Indicators of Poor Water Quality (Group Three)
Measures 1.0 mm to 5.0 cm in length
Typically flattened from the back to the belly
Always have 34 segments
Suckers at both ends
Leeches are common in warm protected waters of
lakes, ponds, streams, and marshes.
• Leeches usually avoid light by hiding under rocks or
among aquatic vegetation or detritus
• Silty substrates are unsuitable for leeches because
they cannot attach properly
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WEF_Macroinvertibrates
3
Midgeflies
Indicators of Poor Water Quality (Group Three)
Midgefly Larvae
Midgefly Larvae
Midgefly Larvae
• Midge Larvae
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Measures up to ½ inch in length
Body small, cylindrical, and slightly curved
Occasionally deep red in color, otherwise variously colored
Two small prolegs just posterior to head
Frequently found in bottom sediments of lakes, streams, and ponds
where they feed on deposited organic material
WEF_Macroinvertibrates
4
Pouch Snails
Indicators of Poor Water Quality (Group Three)
• Pouch Snail
– Shell opens to the left
– Presence of a fleshy “foot” indicates the
snail is alive
– Snails in this category can be distinguished
from “other snails” by the opening of the
shell
– To identify a snail, hold it with the tip of the
shell pointed up and the opening facing
you (as pictured). If the opening is to the left
side, you have a pouch snail
– Do not count empty shells
Pouch Snail
WEF_Macroinvertibrates
5
Other Snails (Including Gilled)
Indicators of Poor Water Quality (Group Three)
• Other snails (Class Gastropada)
– Shell opens to the right
– On most, a covering, called the operculum,
indicates the snail is alive; If no operculum is
present look for a fleshy “foot”
– Snails in this category can be distinguished from
pouch snails by the opening of the shell
– To identify a snail, hold it with the tip of the shell
pointed up and the opening facing you (as
pictured); If the opening is to the right side, you
have a snail that falls in the “other snails”
category, also referred to as “gill-breathing”
snails
– Note: The flat, coiled snails also fall into this
group
– Do not count empty shells
WEF_Macroinvertibrates
6
Blackflies
Indicators of Poor Water Quality (Group Three)
• Blackfly Larvae
– Measure to ½ inch in length
– Body cylindrical and widest at the
posterior
– Abdomen terminates in an attachment
disc
– Head usually possesses fan-like
appendages
– Blackfly larvae prefer cold running
water and are usually found attached
by the end of their abdomens to rocks,
woody debris, or vegetation in the
currents of rivers and streams
WEF_Macroinvertibrates
7
Aquatic Beetle
Indicators of Moderate Water Quality (Group Two)
Head more slender than that of the dobsonfly
6 legs
Some with lateral appendages
Size range: ½” – 1”
Beetle larvae look somewhat similar to dobsonfly
larvae, but are generally smaller in color and
more slender and tapered that the dobsonfly
larvae
• Often the head is darker in color than the rest of
the body
• Beetle larvae will not have pronounced pincers
that the dobsonfly larvae possess
• The appendages on the back section
(abdomen) of this organism, if present are called
“lateral appendages” and should not be
mistaken for legs
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Water Beetle
Beetle Larva
WEF_Macroinvertibrates
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Craneflies
Indicators of Moderate Water Quality (Group Two)
• Cranefly Larva
– Measure 1/3 to 2 inches in length
– Plump caterpillar-like segmented
body
– Head is usually retracted into the
body
– Milky green to brown color
– Four finger-like lobes at back end
of body
Cranefly Larvae
Cranefly Larva
WEF_Macroinvertibrates
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Damselflies
Indicators of Moderate Water Quality (Group Two)
• Damselfly Nymph
– Measures between 0.5 to 2.0 inches in length
– Nymph has large eyes, (or larva) two pairs of
wing pads and a large round or oval
abdomen
– Abdomen terminates in three small pointed
gills
– Can be readily distinguished from other
species by the presence of a large jaw, which
is modified for grasping and covers the
underside of the head
– Prefers still water, often found among
vegetation and leaf packs
Damselfly Nymph
Damselfly Larvae
WEF_Macroinvertibrates
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Crayfish
Indicators of Moderate Water Quality (Group Two)
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Measures up to 6 inches in length
Has 5 pairs of walking legs, the first pair with large pinchers
Resembles a small lobster
Some crayfish are usually active only at night
During the day they hide in burrows or under rocks
Crayfish are omnivorous, eating both plants and animals
Decapoda (Crayfish)
WEF_Macroinvertibrates
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Fishflies
Indicators of Moderate Water Quality (Group Two)
• Mouth has large, chewing pinchers
• Retractable breathing tubes extend from top
of abdomen (not visible without
magnification)
• Smooth underside
Fishfly Adult
• Abdominal segments with many strand-like
appendages extending from each side
• Three pairs of legs on middle section of body
with tiny pinchers at the end of each
• Back end is forked with two short tails and two
hooks on each tail
• Light colored
Fishfly
• Often confused with hellgramite (dobson fly
larva) but does not have fluffy gills on
underside
WEF_Macroinvertibrates
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Sowbug
Indicators of Moderate Water Quality (Group Two)
• Sowbug (Class Crustacea, Order
Isopoda)
– Segmented flat body
– Many legs
– Dimension range: ¼” to ½”
– Sowbugs are gray and segmented with
an “armored” appearance
– They look very similar to terrestrial
sowbugs, also known as pill bugs
– They have a sort of rectangular shape
and many small legs
– Sowbugs are most easily found along
the stream’s edge
WEF_Macroinvertibrates
13
Scuds
Indicators of Moderate Water Quality (Group Two)
• Measures 5 to 20 mm in length
• Clear whitish to pink in color
• Laterally flattened (top to bottom)
• Seven pairs of legs, the first two are modified for grasping
• Found in shallow freshwater springs, streams, lakes and ponds
• Most species feed on debris
• Scuds are an important food source for many fishes
WEF_Macroinvertibrates
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Dragonfly
Indicators of Moderate Water Quality (Group Two)
• Measures between 0.5 to 3.0 inches in
length
• Large eyes
• Two pairs of wing pads
• Large round or oval abdomen
• Abdomen terminates in three small
pointed structures
• Can be readily distinguished from other
species by the presence of a large jaw
which is modified for grasping and
covers the underside of the head
• Prefer still water, often found among
vegetation and leaf packs or burrowed
in sediment
Dragonfly Larva
WEF_Macroinvertibrates
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Dobsonflies
Indicators of Good Water Quality (Group One)
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Commonly called hellgrammites
Measures ¾ to 4 inches in length
Body is elongate and somewhat flattened
Large pinching jaws
Lateral appendages along the length of the
abdomen
Cotton-like gill tufts on underside of abdomen
Abdomen terminates in two small prolegs, each
bearing two claws
Short inconspicuous antennae
Feed on other aquatic insects
Usually found on the underside of large rocks in
cool, slow-moving streams
Handle hellgrammites carefully, larger individuals
may deliver a painful pinch!
WEF_Macroinvertibrates
Close-up of Dobsonfly
Larvae Mandables
Dobsonfly Adult
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Alderfly
Indicators of Good Water Quality (Group One)
• Measure to 1 inch in length
(including tail)
• Abdomen terminates in a single tail
• Lateral filaments along abdomen
• Often pale to deep reddish-brown
in color
Alderfly Larva
Alderfly Adult
WEF_Macroinvertibrates
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Caddisflies
Indicators of Good Water Quality (Group One)
• Up to 1½ inches
• 6 hooked legs on upper third of body
• 2 hooks at back end
• May be in stick, rock or leaf case
with it’s head sticking out
• May have fluffy gill tufts on lower half
Caddisfly Larva
WEF_Macroinvertibrates
Caddisfly Larva
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Water Penny
Indicators of Good Water Quality (Group One)
• Measures ¼ inch in length
• Flat disk-like body
• Head and legs concealed from
above
• 6 legs and branched gills on
underside
• Water pennies prefer cold, fast
moving streams
• Their smooth, flattened bodies
enable them to resist the pull of
the current
Water Penny Larvae
• Water pennies are usually found
on smooth rocks where they
graze on attached algae
Water Penny Larvae
WEF_Macroinvertibrates
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Clams
Indicators of Good Water Quality (Group One)
• Fleshy “foot” (not visible if shells are closed tightly)
• Size range: 1/8” to 5”
• Clams are easily identified by their two shells,
which they will draw tightly closed when handled
• Count only whole, live clams (those with both
shells) in your assessment
Piston Grip
• Please do not force the shells open to see if you
have a live clam; If the shell is tightly closed, you
can assume the organism is alive
• Note: Clams are usually buried in the stream
bottom, so you should kick up the sampling area
thoroughly; Also, as indicated by the size range,
clams can be quite small and fragile, so look
carefully and handle carefully
Pond Mussel
• Do not count empty shells
• Many clams are endangered so immediately
return to the stream where you found them
WEF_Macroinvertibrates
Fanshell
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Gilled Snails
Indicators of Good Water Quality (Group One)
• Up to ¾ inches long
• Shell opening covered by a thin plate called
an operculum
• With helix pointed up shell opens to right
• Intolerant of pollution
• Snails in this category can be distinguished
from pouch snails by opening the shell; To
identify a snail, hold it with the tip of the shell
pointed up and the opening facing you
• If the opening is on the right side, you have a
snail that falls in the “other snails” category,
also referred to as the “gill breathing” snails
• Note: The flat, coiled snails also fall into this
group
• Do not count empty shells
WEF_Macroinvertibrates
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Mayflies
Indicators of Good Water Quality (Group One)
• Mayflies
– Mature larvae measure to ¼ to 2 inches in length (excluding tails)
– Two rows of long hairs present on inside of front legs
– 2 or 3 tails
– Slender antennae
– The conspicuous hairs growing on the inner front legs are used for
filtering food particles from the water
– Brush-legged mayflies may be minnow like with a vertically oriented
head and three tails (as pictured) or may be more flattened with a
horizontally oriented head and two tails
Mayfly Adult
WEF_Macroinvertibrates
Brush-Legged Mayfly Nymph
Mayfly Nymph
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Riffle Beetles
Indicators of Good Water Quality (Group One)
• Riffle beetles measure approximately 1/16 to
1/4 inch in length
• Body small, adults usually oval
• Legs are long
• Antennae are usually slender
• Riffle beetles walk slowly underwater; they
do not swim on the surface
Riffle Beetle Adult
WEF_Macroinvertibrates
Riffle Beetle Adult
Riffle Beetle Larvae
and Adults
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Stonefly
Indicators of Good Water Quality (Group One)
• Stonefly
Measure 8 to 15 mm in length (not including tails)
2 tails
2 sets of wing pads
Sometimes have branched gills between legs on
underside of body
– Yellow to brown in color; often patterned yellow
and brown when mature
– Superficially similar to certain flattened mayfly
nymphs, however stonefly nymphs always have
two tails, prominent antennae, and two claws at
the end of each leg
– Stoneflies are not tolerant to low levels of dissolved
oxygen and therefore prefer cold, swift-moving
streams; The streamlined, flattened bodies of
stonefly nymphs enable them to move about the
rocky streambed in rapid currents
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WEF_Macroinvertibrates
Stonefly Nymph
Stonefly Nymph
Stonefly
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Watersnipe
Indicators of Good Water Quality (Group One)
• Watersnipe Larvae
– Measure 12 to 18 mm in length
– Color varies from pale to green
– Abdomen has well-developed pairs of
ventral prolegs and short dorsal and
lateral filaments
– Posterior pair of processes
– Widespread in well oxygenated
streams and rivers; Some species
burrow in soft sediments
– Carnivorous
WEF_Macroinvertibrates
Watersnip Larva
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