More information on macroinvertebrates
(S = Sensitivity. Low sensitivity 1 & High sensitivity 9 - e.g. S5 medium)
Swimming mayfly (S9)
The larvae of a small number of our mayflies are designed for swimming unlike
most mayflies that are designed to avoid being washed off the streambed. The
most common swimming genus is Nesameletus. This mayfly is streamlined in shape
and the three tails are feathered to act like a flat tail to assist with
swimming. Nesameletus is very similar in shape to Rallidens; another swimming
mayfly, and both genera can beat the gills along the body when at rest. The
gills of Nesameletus are single and leaf-like, while Rallidens has tufted gills
between the leaf-like gills.
Swimming mayflies are usually found in clean, cool waters in stony streams.
They are a useful indicator group because an abundance of swimming mayflies is
only likely to occur where water quality is high and conditions should be
suitable for a range of other "sensitive" species.
This is New Zealand's most common and widespread mayfly. Note the three long
tails, a feature typical of mayflies. The larvae are aquatic and their flat
bodies allow them to hold on to stones in fast flowing streams. Like most
mayflies they have leaf-like gills along the sides of their body. In many
mayflies these gills are arranged in pairs, but in Deleatidium the gills are
Deleatidium prefers cool water and is most common in mountains and bushy
areas. An abundance of this mayfly at a site is a sign of good water quality.
Deleatidium grazes algae from the beds of streams, but is not found in
streambeds that are too heavily covered by algae.
Deleatidium larvae provide an ideal food source for fish so their abundance
can increase the growth rates and size of fish in rivers.
Double-gilled mayfly without spines (S7-9)
There are lots of different types of mayflies that live in stony streams. One
of the common types is Austroclima, one of the "double-gilled" group. The term
double-gilled refers to the paired gills attached to the sides of the abdomen.
Unlike some mayflies, Austroclima does not have strong spines along the sides of
the abdomen. The low-lying body is designed to sit flat on stone surfaces in
fast-flowing water, and they can be hard to see if they are not moving. If
placed in a white tray in a bit of water, the three long tails can be seen.
Austroclima is quite fussy about water quality and you are unlikely to find
them in waters that warm up to more than 20 degrees Celsius. This mayfly grazes
on thin films of algae on stony surfaces, but it does not cope well with
streambeds that are overloaded with nutrients and heavily smothered by algae.
Spiny-gilled mayfly (S7-9)
Possibly the most distinctive mayfly found in New Zealand streams is the
spiny-gilled mayfly Coloburiscus. Like all mayflies, Coloburiscus has three
tails, however the middle tail is quite small and can be easily overlooked. As
the name suggests, this mayfly has distinctive spiny gills protruding from the
abdomen. The mayfly has an unusual feeding mechanism, using its very hairy legs
to filter food particles drifting in the stream.
Coloburiscus is very fussy about water quality. It cannot beat its gills to
aid "breathing" and therefore requires high dissolved oxygen levels in the
water. Clean, cold, fast-flowing streams provide high dissolved oxygen levels
and therefore this is where Coloburiscus is most abundant.
Forest cover also suits Coloburiscus because lots of small food particles
originate from forest leaf litter dropping into the water.
Swimming mayfly (S7-9)
Rallidens has a streamlined shape and feathered tail that allows it to swim.
When at rest in calm waters, it beats its gills to keep oxygen-carrying water
moving past them.
Rallidens is usually found in high quality, well-shaded streams with cool
water. This is typical of the mayflies - they generally require high dissolved
oxygen levels and this requires cool temperatures. If you find lots of this
mayfly species at a site, you're probably looking at a good quality stream with
a wide variety of other stream insects.
Double-gilled mayfly with spines (S7-9)
One of the most common mayflies found in tree-covered streams is Zephlebia.
Like its cousin Austroclima, it is a "double-gilled" mayfly having paired gills
attached to the sides of its abdomen. Zephlebia has strong spines along the
sides of the lower abdomen, and some Zephlebia a have spectacular pattern of
light and dark patches on the body and legs. It is often found clinging to
submerged bits of wood and the under sides of stones. These stable surfaces
provide shelter from the water current, and provide food in the form of organic
material including algae. Zephlebia tends to be more common and larger than its
cousin Austroclima and is therefore often one of the first mayflies observed
when you look closely at the streambed.
Zephlebia is another invertebrate likely to be found in (or close to) areas
that are well shaded by trees, and is unlikely to be found in waters that warm
up to more than 20 degrees Celsius.
Stoneflies are ancient insects, most of which have aquatic, or semi-aquatic
nymphs (immature stages). Zelandobius is one of the more common and smaller
stoneflies. These insects have two tails (distinguishing them from the
three-tailed mayflies) although sometimes the tail filaments are short and hard
to see. Zelandobius belongs to a group that have a small tuft of gills between
the two tails. Stoneflies are more able to crawl out of the water and they
resist drying out better than the mayflies do.
Zelandobius can be found in high quality and medium quality streams. They can
be abundant in both fine gravel (almost sandy) riverbeds and in stony beds with
large stones. Zelandobius is more tolerant than most of the larger species of
stoneflies which require very cold water temperatures.
Acroperla is a stonefly that is very similar in shape and size to its cousin
Zelandobius, a mayfly. Both have a small tuft of gills between the two tails,
but Acroperla has distinctive pale markings on the legs and abdomen. Like
Zelandobius, Acroperla is quite capable of spending time out of the water and is
generally much more mobile "on foot" than the mayflies.
Some species of Acroperla live around the margins of lakes, while other
species occur in high quality, fast-flowing mountain streams where some of the
largest stoneflies live. Acroperla can tolerate a bit of stream warming, but
shallow and slow-flowing streams that are completely unshaded, may get too warm
Smooth-cased caddisfly (S9)
The larva of the smooth-cased or horny-cased caddis Olinga is a common
inhabitant in cool, clean streams. Very young Olinga attach small sand grains to
their protective cases, but before long they stop using sand and construct
smooth, shiny orange or red-brown cases in a slightly curved tube shape. This
caddis larva grazes algae but also feeds on decomposing leaves that have fallen
Their preference for cool water and their appetite for decomposing leaves
means that they are often found in native forest streams, although they are also
quite happy to feed on the leaves of introduced willows. Olinga is a useful
indicator of good, cool water quality.
Dark-headed free-living caddisfly (S7)
Costachorema is one of the larger free-living
caddis flies in our streams.
These caddis larvae don't hide their soft bodies in portable cases, hence the
term "free-living". At the pupa stage however, they construct protective stony
"houses" attached to stable rocks, for the transition from larva to winged
adult. Costachorema larvae have larger and darker heads than most other
free-living caddis flies.
Costachorema isn't as common as it's cousin Hydrobiosis, but both genera
often occur together in clean, stony streams, often in steep mountain or hill
country areas. If streams become silty due to erosion or upstream earthworks,
species like Costachorema that are usually found on clean stony beds are likely
Small-headed free-living caddisfly (S6)
Many types of
caddisfly larvae construct and carry their own mobile shelters,
but there are also several types of free-living caddis that don't carry such
shelters. One free-living genus is Neurochorema, which often seems to have a
small head in proportion to the body size. A dark rectangular pattern can be
seen on the top of the head of some Neurochorema.
Neurochorema is usually found in the upper to midreaches of stony streams in
areas of high to moderate water quality. This caddis is usually less common than
other free-living groups such as Hydrobiosis and Costachorema. Neurochorema is
one of many groups that survive best in cool stony streams rather than warm,
Free-living caddisfly (S5)
Hydrobiosis is a
caddisfly that does not shelter in a portable case, hence
the common name "free-living caddis". The larva of Hydrobiosis often has a
bright-green body, though some species are very pale. There are several other
genera of free-living caddis flies but Hydrobiosis is probably the most common.
Before emerging from the stream as a flying adult, free-living caddis pupae
shelter in hideouts made of sand attached to stable stones.
Hydrobiosis larvae can be found in waters of moderate or high quality, but
not usually in heavily-polluted waters.
Stony-case caddisfly (S5)
There are several
caddisfly species with larvae that construct protective
tubes out of sand or fine gravel. Pycnocentrodes is the most common of these.
This caddis uses variable sizes of fine gravel, with the largest pieces towards
the widest (opening) end of the tube. The related Pycnocentria arranges more
uniform sized sand particles into neat spirals. The larva eventually seals the
tube for the pupa stage, when the transformation into the winged adult occurs.
The stony cases don't stop fish feeding on these caddis flies, but they would
surely be less appealing as food items than the free-living (non-cased)
These cased caddis flies can be abundant in clean streams, but they are also
found in farmland and sometimes in urban streams. Like most caddis flies they are
most commonly found in cool, flowing waters.
Stick caddisfly (S5)
If you've ever looked closely into a stream and noticed a stick walking
around the bed, you've probably been looking at a young Triplectides. This is
the stick caddis, an aquatic insect with a larva that hides its soft body inside
hollow bits of stick. If there are no hollow sticks, they will construct a tube
out of small bits of plant, sand and even snail shells. Often the only sign of
the caddis is the stripy legs at one end of the stick or tube.
Triplectides prefers slow-flowing streams, especially those running through
bush where there is a good supply of potential homes. This caddis larva can be
found in a wide range of stream types, though not in heavily polluted streams.
Net-spinning caddisfly (S4)
Insects were using nets to collect food from streams many millions of years
before humans came up with the idea. The larvae of the net-spinning caddis
Aoteapsyche (and close relative Orthopsyche) construct small nets and attach
these to stones to catch small food items drifting downstream. Net-spinning
caddis larvae don't make the portable cases several other types of caddis do,
although they shelter in homes made of tiny stones fixed to the same rocks as
Aoteapsyche is found all over New Zealand in high quality and moderately
degraded waters. Huge populations of this caddis can be found on the beds of
lake-outlet rivers, as they can feed on the tiny creatures (zooplankton)
drifting out of the lake. The more sensitive Orthopsyche is only found in the
North Island, usually in "clean water" streams. Both can be important items in
the diets of freshwater fish, especially at the vulnerable stage when they
emerge from the water surface as adults.
The largest of all stream insects in New Zealand is the dobsonfly
Archichauliodes. This insect is also known as the "toebiter" and the 5cm long
larvae can inflict a good nip. The dobsonfly larva is an unusual-looking
creature with leg-like gills along the abdomen, and fierce-looking jaws that are
used to catch and eat other stream insects. The jaws are powerful enough to give
small fish a nasty surprise if they dare attempt to eat a large dobsonfly larva.
Dobsonfly larvae can be found in clean and moderately degraded stony streams.
They are very tough, being able to survive freezing and being out of the water
for several hours. Adult Dobson flies are spectacular insects with a wingspan of
Xanthocnemis is a damselfly that you often see hovering over streams and
ponds. Adult damselflies are similar to small dragonflies, but only damselflies
can fold their wings back along their body when they land. There are three
leaf-like gills at the end of the body.
Xanthocnemis larvae are aquatic, living in slow-flowing waters, often amongst
weed beds. These insects are predators that catch prey with their extendable
jaws. Being larger than most aquatic insects, damselflies are favourite food
items for fish.
Damselfly larvae can be found in clean and not-so-clean waters and they are
quite tolerant of low dissolved oxygen and warm water temperatures.
Crane fly larva (S5)
The larvae of several species of long-legged crane flies live in New Zealand
streams. The most common of these is Aphrophila, which has a maggot-like larva
with "creeping welts" along the body that resemble the suckers used by
caterpillars for attachment. The head of the larva is often retracted into the
body and can be hard to see. Aphrophila larvae are carnivores, feeding on other
Aphrophila larvae are found in high quality and moderate quality streams.
They can be abundant in fine gravel streambeds and also amongst algae-covered
Riffle beetle (S6)
Elmids are the most common beetles in New Zealand streams and rivers. Elmid
larvae are long and slender, while the adults are more chunky and typically
beetle-like. Both can be found on the beds of stony or gravelly rivers, in clean
mountain streams, bush-covered streams and unshaded farmland streams. They are
sometimes the most abundant insects in a stream community, and they can make up
an important part of the diets of freshwater fish.
Sand fly (S3)
If you've ever been to Fiordland or if you've been close to a stream and been
bitten by small black flying insects, chances are you've met Austrosimulium. The
larvae of these sand flies (or black flies) live in both stony and weedy streams
where they catch drifting food in their fan-like mouthparts. It takes a keen eye
to see these insects without a magnifying glass, but sometimes they can be seen
attached to surfaces by their rounded tail-end.
Sand flies are not necessarily good indicators of water quality unless you can
identify the species. Some species of Austrosimulium are commonly found in
clean, stony mountain streams, but others are very common in slow-flowing,
nutrient-enriched lowland streams
True fly (S2)
Midge larvae (juveniles) are among the most widespread and abundant of all
freshwater creatures. People living beside lakes, ponds and streams often notice
swarms of mosquito-like insects, which are the non-biting adults of these
midges. Orthoclads are one of the larger groups of midges in New Zealand. Midges
are members of the "true flies" which have adults with only two wings (most
other flying insects have four wings). The larvae of the true flies are
generally simple in design, being often worm-like in shape. Orthoclad larvae
typically have a green worm-like body with a head that contains the only hard
Orthoclad midges are often found amongst thick algae growths in streams that
have high levels of nutrients (such nutrients may be of natural or unnatural
sources). Some can tolerate warm water temperatures and quite low levels of
dissolved oxygen. Midges can be the most abundant creatures in streams that are
in quite poor condition.
Pond snail or Mud snail (S4)
The most common freshwater snail in New Zealand is the pond snail
Potamopyrgus. In fact this New Zealand species has been introduced to several
other countries and is now the most common freshwater snail in Britain!
Potamopyrgus is also considered a pest in Australia and North America. It is
very hard to control because it reproduces quickly and the chunky shell makes it
of little food value to fish. This is one of many examples of species causing
problems following careless introductions by humans.
Potamopyrgus is an important grazer in New Zealand rivers as it can control
the amount of green or brown algae on riverbeds. Potamopyrgus can't hang on to
the riverbed in fast-flowing waters so is not found in rapid currents or after
Introduced freshwater snail (S3)
One of the common introduced invertebrates in our streams is the snail Physa.
This small snail is more rounded than our native Potamopyrgus, and the opening
(aperture) is on the opposite side of the snail to Potamopyrgus. The shell of
Physa is often so thin that you can see right through into the body inside.
Physa thrives in streams that are heavily enriched with organic matter. Their
numbers can increase rapidly, as they become mature in only ten weeks. This
snail may be found in high abundance with oligochaete worms in streams
downstream of treated sewage discharges. Physa grazes the prolific algae and
other microscopic life forms attached to the streambed or to plants in such
Luminescent limpet (S7)
Lots of creatures around the world have the ability to glow in the dark, but
only one of these lives in fresh water and it is found only in the North Island
of New Zealand. This mysterious creature is the freshwater limpet Latia
neritoides. Latia is related to the land snails and has evolved a limpet-like
shell shape to cope with flowing waters. Latia attaches to the clean surfaces of
stones, bits of wood and sometimes water plants in gently-flowing streams. They
are not found in streams that are too warm or streams that have too much algal
This amazing limpet can release a glow-in-the-dark (luminescent) green slime
when disturbed. One theory for the apparent success of this strategy, is that a
night time predator such as an eel, having disturbed the limpet, will see the
glowing slime being carried away by the stream current and will chase the light
rather than the limpet. It is also possible that some of the glowing slime may
stick to the predator making it more at risk of being eaten by even bigger
predators - it's probably hard to hide in the dark when you have glowing mucus
clinging to you.
Amphipods are crustaceans that include the
"sand hoppers" that you often see
on the beach when you lift bits of driftwood or seaweed. There are several types
of amphipods that live in fresh water but easily the most common type around New
Zealand is Paracalliope. This amphipod is most abundant in lowland streams,
particularly in slow-flowing reaches where they may shelter amongst weed beds.
Fast-swimming Paracalliope are often the first animals observed when a handful
of aquatic vegetation is placed in shallow water in a white tray.
Paracalliope and other amphipods may be very important food sources for
native and introduced freshwater fish in the lower reaches of rivers. They can
be abundant in rivers that have considerable nutrient enrichment from farmland,
but they can suddenly decline after floods or after severe pollution events.
Paratya is New Zealand's most common freshwater shrimp. These shrimps are
often found in streams near the sea because they spend part of their lives in
seawater. They graze algae and other microscopic life growing on streambeds.
Their constant feeding off the bottom makes them useful cleaners in freshwater
Shrimps aren't fast swimmers so they're best suited to slow waters, and are
often found amongst weed beds. When they migrate into freshwaters, they can
climb some waterfalls and dams, because their claws can grasp most rough
Very high or smooth dams will stop shrimps from migrating upstream however; a
problem also faced by many of our native freshwater fish that also migrate to
and from the sea.
Freshwater crayfish (S5)
Freshwater crayfish are the largest of all our freshwater invertebrates and
are not macroinvertebrates. They are also known as koura, crawlies or
Paranephrops (genus name). They can grow to a good edible size and they are
farmed in New Zealand. Large individuals, especially those in lakes, can give
you a powerful nip with their pincers.
Crayfish are omnivores, feeding mostly at night on both plant and animal
matter. During the day they hide amongst stones, under woody debris, amongst
weeds or in their own burrows in soft sediments. They are seldom found in urban
streams, because of a lack of hiding places, poor water quality and the severe
flash-flooding nature of streams that are fed by city stormwater networks.
Freshwater crab (S4)
There is one truly freshwater crab in New Zealand, and little is known about
its biology or natural distribution. The scientific name of this crab is
Halicarcinus lacustris and it should not be confused with the mud crabs
(particularly Helice crassa) that are often found in river estuaries.
Halicarcinus is found in streams and lakes in the Waikato and Auckland regions,
but their numbers may be decreasing because of habitat change and predation by
In Waitakere City's Oratia Stream, large numbers of these small crabs can be
found hiding in crevices in rotting logs. Such "woody debris" in streams
provides important habitats for many other stream invertebrates and fish
especially in sandy-bedded streams such as the Oratia. Maintaining a supply of
woody debris is simple; protect or plant suitable trees along stream margins.
Trees also create the shade that cools stream water, allowing the many
temperature-sensitive invertebrates to survive. The crabs also need shade to
see, because their sensitive eyes are not designed to cope with bright light.
Aquatic earthworm (S5)
Oligochaetes are segmented worms that include the common garden earthworms,
as well as a number of aquatic species. Aquatic oligochaetes can be found in
almost all streambeds, particularly where there is abundant organic matter for
food. Some oligochaetes are extremely abundant in waters polluted by organic
wastes such as treated sewage. Some very small oligochaetes live amongst mats of
algae on the streambed.
It is often considered to be a sign of poor stream health when oligochaetes
are the most abundant invertebrates in a streambed community, especially when
there are few or no sensitive insect groups. The presence of a few oligochaetes
in a diverse community is not a sign of poor stream health however, because some
oligochaetes can live in the most pristine habitats. The large earthworm-like
Eiseniella can be found in both high quality and low quality waters.
Flatworms are among the weirdest yet most common creatures in many streams.
Their amazingly flexible bodies are well worth watching under a magnifying glass
or microscope. The common freshwater species usually have two distinct eyes that
have a cross-eyed appearance. Most flatworms are shaped like flat slugs and live
on stones and plants, but one species, which lives on the skins (especially
claws) of freshwater crayfish, is shaped like a small, round hand complete with
Some flatworms are quite tolerant of poor water quality and they can be among
the most common creatures in city streams and enriched farmland streams. Quite
different species of flatworms occur in clean mountain streams however, so it
pays to know which species is which if you want to use them as indicators of
Many people are surprised to learn that we have leeches in New Zealand
streams. In fact they are quite common, particularly in slow flowing or still
waters. Most of these leeches are small, pale-coloured species that feed on
other invertebrates and are not likely to attempt to feed on humans. Leeches
have strong suckers under the body and they can be difficult to remove from
stone or plant surfaces. Their flexible bodies may resemble flatworms at first
glance, but flatworms have much softer bodies than leeches.
Because leeches are usually found in slow-flowing waters, and these habitats
are more likely to have poor water quality, the leeches are often associated
with "tolerant" invertebrate species. They do not necessarily indicate poor
water quality however, and probably occur in such waters because their food
sources (possibly aquatic worms and snails) live in these habitats.