Identification Keys

Citizens’ Environment Watch: Key to Benthic Macroinvertebrates
For more information, please see: www.citizensenvironmentwatch.org
B.MI.
No legs
Long
tentacles at
one end
Shell
Non-segmented body
2
shells
Not to Scale
Segmented body
1
spiral
shell
Miniature
earthworm
look-alike
Clam
(Pelecypoda)
Graph does not depict
evolutionary relationships.
Round Body
Flat
body
Snail
(Gastropoda)
Hydra
(Coelenterata)
Short,
pointy,
chubby body
Maggot
look-alike
Large, chubby
cream or light
grey body
Bare
body
Body with
Clitellum
7 pairs of
bumps on
abdomen
Transparent,
guts visible
Thin, tiny,
long, with
no surface
features
1 pair of
prolegs just
below head
Some have
segments with
hooks
Short appendages
at one end with
holes in-between Body seems
like beads
Some might
or opened
have a long
necklace
thin tube at
one end
Pair of
prolegs
with hooks
at posterior
end
Very flat
Flatworm
(Turbellaria)
Segmented
Suckers at
both ends
Leech
(Hirudinea)
Roundworms
(Nematoda)
Horsefly
larvae
(Tabanidae)
Aquatic
Earthworm
(Oligochaeta)
Cranefly
(Tipulidae)
Misc. True fly
larvae
(Diptera)
Head with
folding pair
of fans
1 pair of
prolegs just
below head
Rounded
head with
constantly
moving
mouth parts
Constantly
surfacing for
air
Midge larvae
(Chironomidae)
No-see-ums larvae
(Ceratopogonidae)
Mosquito
larvae
(Culicidae)
Blackfly
larvae
(Simuliidae)
Comma (,)
shaped with
large head
with
“horns”
Caterpillar
look-alike
Some might
be hairy
Body with
hairs at both
sides
Posterior
half of body
swollen
Small orange
pointy-head
with tiny eyes
Nonsegmented
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page
Legs
Fast
moving but
tendency to
float
Often
wrapped
around
aquatic
plants
Mosquito
pupae
(Culicidae)
Aquatic Moths
(Lepidoptera)
B.MI.
Previous
page
No legs
Graph does not depict
evolutionary relationships.
Legs
More than 3 pairs of legs
Shaped like
tiny dot
Shrimp
look-alike
Flat body
Body
segments
loosely
connected,
each with a
pair of legs
4 pairs of
legs
Body
compressed
laterally
(Flat
sideways)
Spider
look-alike
Looks
like
small
lobster
Long
slender
abdomen
ending with
3 featherlike gills
(Featherlike gills
can be lost
easily)
Dark stout
body
Round
abdomen
with pointy
tailless end
Head with
no visible
antenna
Head with
long
moving
antennae
Fast swimmers
for shorts
periods of time
Very short
antenna
Soft
abdomen
rolled over
belly
Gray
rectangular
abdomen
with 2 long
tails
Fast
crawling
Crayfish
(Decapoda)
Dragonfly
(Anisoptera)
Water mites
(Hydrachnidae)
Immobile
shorn-like
filaments
on both
sides of
abdomen
Looks like
Hellgrammite
without thornlike structures
on both side of
abdomen (see
left)
Strong,
smooth,
shinny
body. Oval
or rounded
Hardened
wings with
posterior
half of one
overlapping
the other
Mouth with
strong
mandibles
Crawling, never
swimming
Aquatic
sowbug
(Isopoda)
Head very
close or
fused to
body
3 dark
plates just
below head.
Legs only
from these
segments
Legs or
appendages
in all body
segments
Some might be
velvet red
Not to Scale
3 pairs of legs
Some make
cases with
twits and sand
Many
feather-like
gills at both
sides of
abdomen
(sometimes
flapping
constantly)
Stonefly
(Plecoptera)
No antenna
Dark stout
head with
large
mandibles
and short
antenna
Mouth
formed into
cone or
long narrow
tube for
sucking
Slender, sometimes
short- legs
Hellgrammite
(megaloptera)
Beetle
(Coleoptera)
Scud
(Amphipoda)
Damselfly
(Zygoptera)
Caddisfly
(Trichoptera)
Mayfly
(Ephimeroptera)
Beatle larvae
(Coleoptera)
Aquatic
true bug
(Hemiptera)