A variety of animals live in water, they are also collectively called macroinvertebrates. Some of them can serve us as indicator organisms, because they only occur under certain conditions. There are those that can only live in oxygen-rich, clear and fast-flowing waters - such as some caddisfly larvae in a stream. And others that have no problem living in a dirty pond - like the larva of the dung bee. Based on our observation of the water (color, smell, temperature, etc.) but also on the fauna, we humans can tell something about the quality of the water in front of us. Looking closely and knowing about the species is an important part of water body assessment. Here are shown some organisms that are suitable as bioindicators.


Chart for an overview of insect larvae living underwater



 The caddisfly larvae are of great importance for a water body. They can be divided into two groups. The caddisless larvae and the caddis-bearing larvae. The quiver-bearing larvae build their caddis from their own produced spider silk and incorporate various materials from their habitat into it. The material is extremely diverse and can be constructed from grains of sand, sticks, shells, spruce needles, or pieces of leaves. It serves to protect the larvae and is their home that they constantly carry around. The caddis is always expanded by the growing larva. In fast flowing streams heavy material is often used such as stones or sand. Caddisless larvae usually live in waters with enough current to keep their (tracheal) gills well supplied with oxygen. They look caterpillar-like and spin a kind of funnel into the current, in which microorganisms, algae or dead plant material collects which serves as food for them. Some caddisless larvae are also active hunters. Caddisfly larvae are only able to survive in clean or slightly polluted waters. They can often be found in groups under stones.

The adult caddisflies are unimpressive, gray-brown flying insects that hide during the day in moss and deadwood or under leaves of plants near the shore. Towards evening they dance in swarms at the water's edge and are then often mistaken for mosquitoes or moths. Unlike moths, however, they carry their antennae long and pointing forward.

 caddisfly colony under stone

A accumulation of caddisflies under a stone of a stream in Rhineland-Palatinate, Germany


Photo from GLOBE Swiss



N Koecherflieg 3

N Koecherflieg 1

Example of a caddisless larva and a caddis-bearing larva.

Drawings from Kosmos Publishing House




N Koecherflieg 4

An adult caddisfly, it is usually grayish brown in color and inconspicuous.

Drawing from Kosmos Publishing House

Köcherfliege adult

Their coloring reminds of small moths

"Caddisfly (Trichoptera sp.)" by acryptozoo is licensed under CC BY 2.0.





The two developmental stages of the mayfly. On the left the larva, recognizable by the 3 long body appendages, the gill leaves are on the side of the body. On the right the imago recognizable also by the 3 long appendages and the straight erect pairs of wings in the resting state.

The mayflies have nothing to do with the real flies. The larvae live in the water and are clearly recognizable by their 3 long (difference to stoneflies!), thread-like body appendages. In flowing waters they usually burrow into the mud of the water bottom and actively filter the water for food (detritus). In still waters, swimming mayfly larvae also occur. They can be observed sitting on leaves of aquatic plants, where they also find the algal cover as food. They are often yellow with brown markings and are found in clear oxygen-rich waters. The larvae are often only 8 to 23 mm long. Sometimes their skin is found on surrounding shore plants. This is because before their last molt, the larvae usually climb ashore. There, a preliminary stage of the adult mayflies (subimago) hatches within a minute. The mayflies are the only species that then complete another molt (imago). The adult mayflies live only a few hours or usually two to three days, depending on the species. During this time they are looking for a mating partner and do not eat anything.

 EIntasfliegenlarve Gutland Tiefland

A mayfly larva of the Heptageniidae family, It can be found in rivers and streams of the Gutland and also in lower reaches of the Sûre and Moselle rivers.

"Mayfly nymph of the family Heptageniidae" by Dr 'B ' is licensed under CC BY-NC-SA 2.0.

 Eintagsfliege grabend koll Gutland

This is the adult mayfly of the species Ephemera danica, its larvae are burrowing and occur in some streams of the colline stage of the Gutland.

"ephemera danica may fly" by Nick Goodrum Photography is licensed under CC BY 2.0.


Other forms of mayfly larvae

Photo from GLOBE Swiss




 N Steinfliegen 1N Steinfliegen 2

On the left is a stonefly larva and on the right is the adult stonefly, they can be clearly identified by the filamentous appendages on the abdomen, of which they have only 2. Also, the adult stoneflies fold their wings over their back. They are not erect as in mayflies.
Larvae of stoneflies belong to the typical inhabitants of flowing waters. A high number of species indicates good water quality. They resemble the larvae of mayflies, but have a clear distinguishing feature: they always have only 2 filamentous appendages on the abdomen. They live in springs, fast flowing streams and rivers and depend on the high oxygen content of the water. In addition, they prefer streams that are cold even in summer. They are extremely sensitive to pollution and are therefore good bioindicators of unpolluted waters. They are shy of light and usually stay in low flow areas such as between larger stones or hidden in aquatic plants.
There are three sizes of stoneflies. The small species feed on algae, the medium ones eat small animals and detritus and the large species prey on other small invertebrates. The 2 long antennae are the organs of touch and taste.

The adults are usually dark brown, black or greenish-yellow in color. They live only a few weeks, essentially staying hidden in semi-darkness and looking for mating partners in moss cushions, under leaves or on furrows of tree bark. They are not good flyers and prefer to crawl away when disturbed.

 Isoperla larva

"Perlodid stonefly, Isoperla sp." by henricksrobert is licensed under CC BY-SA 2.0.

Isoperla adult

"File:Perlidae - Isoperla carbonaria.jpg" by Hectonichus is licensed under CC BY-SA 3.0.

Larva and imago of the genus Isoperla, they are found in streams at medium altitudes in the Ösling and Gutland. The larvae are yellowish with brown-black pattern, which is very individual that means differs from larva to larva. The imagos are also greenish-yellow.


Stonefly larvae can be clearly identified by their TWO filamentous appendages on the abdomen.

Photo from GLOBE Swiss






Mücken Fliegen

Most mosquito and fly larvae as in the illustration above can survive well in nutrient-rich waters, but not species of the blackfly larva (Simuliidae) Illustration and photo below. It is an exception because it helps purify the water with its fan-like bristles with which it filters food from the water. It is only half an inch in size and difficult to spot. It crawls along water plants like a caterpillar and attaches itself to leaves with its adhesive disc. It can be found only in flowing waters, it lives in oxygen-rich streams and rivers of the Ösling and Gutland. Eggs are laid in running water, and the larvae attach themselves to rocks. Breeding success is highly sensitive to water pollution


Kriebelmückenlarve schemaBlackfly larvae are up to 15mm long, it lives in running waters and attaches itself to stones and plants with its adhesive foot at the rear end. It moves forward like a caterpillar. The comb-shaped fan serves the larva to filter and eat small material from the water. Such as algae cells or detritus.
The fan is always turned against the direction of the current.





Mosquitoes (Culicidae)

 Stechmückenlarven puppe

"Culex sp larvae" by (Image: James Gathany, CDC) is licensed under CC BY 2.5.

A group of mosquito larvae in the center you can see a pupa of a larva, soon the adult mosquito will hatch from it.

Mosquitoes have no demands on their water bodies and colonize any still water, including small bodies of water such as puddles or rain barrels. They hang upside down under the surface of the water and scour the water for food particles. Their breathing tube is in contact with the water surface. Mosquito larvae are usually white or yellowish, about 10mm long and have a rather large head with 2 eyes. The larva of the invasive tiger mosquito also looks like this and can hardly be distinguished from the native species. The larvae pupate before the adult mosquito hatches from them, at this stage the mosquito pupa looks different again.
The female adult mosquitoes are bloodsuckers because they need the blood to mature their eggs. The males, on the other hand, feed on flower nectar and dance in swarms on the shore.

   Stechmuecke culexTigermuecke







Mosquito of the family Culex (left) and the invasive species tiger mosquito (Aedes albopictus) (right).

"Culex tarsalis" by Esteban Armijo is licensed under CC BY 2.0.

"Aedes albopictus (Asian Tiger Mosquito)" by Mosquito Addict is licensed under CC BY-NC 2.0.



Chironomids (Chironomidae)

Chironomids (nonbiting midges or lake flies) larvae also have an elongated worm-like shape and can be different colors. They live differently some live freely in the water and are up to 2 cm in size and white, yellowish, green or brown-gray. Andre larvae live in the mud and are light to dark red. They do not need a breathing tube, as they absorb oxygen from the water through their skin. The red forms in particular can still survive in eutrophic waters with little oxygen, as their red pigment helps them still draw residual oxygen from the water. The adult mosquitoes do not bite, even though they look very similar to mosquitoes.


Hover flies (Syrphidae)

Larvae of hover flies live in nutrient-rich, stagnant or slow-flowing waters. They also tolerate heavy pollution and are also found in very small bodies of water such as septic tanks, sewage ponds or brackish water puddles. Such as the larvae of the common drone fly (Eristalis tenax), also called "rat-tailed maggot", which is actually the long breathing tube of the larvae. They live in the mud or sometimes float on the water surface and are relatively large at 10-25 mm. The adult hoverfly is a flower visitor.

 Rattenschwanzlarve Eristalini

The larva of Eristalis tenax, also called rat tail larva.

"File:Langegg Rattenschwanzlarve Eristalini.jpg" by LoKiLeCh is licensed
under CC BY-SA 3.0.


The adult hoverfly Eristalis tenax.

"Eristalis tenax" by Gilles Gonthier is licensed under CC BY 2.0





N Kaefer 2N Kaefer 4N Kaefer 1N Kaefer 5N Kaefer 8N Kaefer 6

Most beetle species whose larvae and beetles live in water belong to the groups of water beetles (Dytiscidae) or true water beetles (Hydrophilidae). The forms of the beetle larvae are very diverse, which is why it is often not possible to identify them immediately as beetle larvae (see schematic illustration above). Larvae of the water beetles and the beetles themselves are both predatory and feed on other small aquatic animals, species of the water beetle group also feed on algae and aquatic plants. Water beetles are usually very small and rarely grow over 1 cm in size. Exceptions are the conspicuous animals living in lakes and ponds, such as the great diving beetle Dytiscus marginalis, the broad-edged beetle Dytiscus latissimus or the great silver water beetle Hydrophilus piceus.


 Gelbrandkäfer Dytiscus marginalis

One of the largest beetles in our waters: Yellow blister beetle Dytiscus marginalis.

"File:Gelbrandkäfer (Dytiscus marginalis).jpg" by Holger Gröschl is licensed under CC BY-SA 2.0.


Stenelmis canaliculata a hooked beetle, it is also found in the lower reaches of the Sûre and Moselle rivers. It is only 4-5mm in size.

"Stenelmis canaliculata (Gyllenhal, 1808)" by christoffer.fagerstrom is licensed under CC BY-NC 2.0.

Species of hooked beetles (Elmidae) are most common in Luxembourg waters. They need a lot of dissolved oxygen in the water for their complex underwater respiratory supply. Thus, they prefer cold, flowing, oxygen-rich water and are thus found in streams or lakes with a lot of water movement. All cleanliness characteristics for bodies of water. They use their hooks on the ends of their legs to claw at aquatic plants, stones or leaves. They are tiny, with a body size of up to 2.5mm, and even their larvae, which look similar to a brown elongated isopod, are only a bit larger (3-4 mm). Therefore, they are not so easy to spot. The beetles and the larvae eat dead plant material and algae from e.g. stones. Hooked beetles are not swimmers, they walk slowly underwater.

 N Kaefer 3N Kaefer 7

The isopod-like shape of a hooked beetle larva
and a beetle of the family Hydraenidae, of which the species
the species Hydraena pulchella also occurs in larger rivers of the Oesling.



Marked as other animal?

BUGS: Semiaquatic bugs (Gerromorpha) and water bugs (Nepomorpha)

Bugs can also look so similar to beetles, you can distinguish them by some features:

  • Bugs have sucking proboscis, beetles have biting and chewing tools.
  • You can't see wings in beetles, they are mostly hidden under the carapace. In bugs you can see their wings, which they have folded over their back.
  • Most species of bugs are predators, feeding on any insect that overpowers them. They sit on aquatic plants, in mud, or on old leaves where they lie in wait for food. Even small fish and tadpoles are eaten.

 N Wanzen 1N Wanzen 3N Wanzen 6N Wanzen 4N Wanzen 2N Wanzen 8

Especially with the water scorpion (third from left in the picture) one could think it would be a beetle, water striders also belong to the bugs. The backswimmer (rightmost picture) has the characteristic to swim with the belly upwards just below the water surface. So it lies on its back.




N Libellen 2

V Insekten 2


There are 2 major groups of dragonflies, the damselflies (left) and the true dragonflies (right). All larvae live in water but look different. The larvae of the damselflies have 3 leaf-like appendages on the abdomen, these are their gill leaves. Damselflies are slender and elongated in shape and usually have a brown-yellow to gray coloration. The larvae of the true dragonflies do not have tail gill leaves, their gills are hidden in the abdomen. They have more of an oval shaped body and also have a "catching mask" on their head that allows them to dart forward to grab their prey.

All dragonfly larvae are hunters and lurk among plants or almost completely hidden in the mud for other aquatic insects, worms or even tadpoles. Before its final molt to adult dragonfly (imago), the larva climbs out of the water and clings to riparian plants. At the back, its skin bursts open and a soft, pale dragonfly squeezes out. From hatching to the first flight of the dragonfly usually takes several hours, the skin (exuvia) remains on the plants and can be discovered by nature observers.



The development of the White-legged damselfly (Platycnemis pennipes) and the Beautiful demoiselle (Calopteryx virgo) is more likely in clean waters with sufficient plant growth and structure. Natural river courses with many marginal areas, with aquatic and riparian plants are optimal for dragonflies. One can only speak of indirect bioindicators for good or near-natural water quality. The Beautiful demoiselle can be found in some river courses of the Ösling, it prefers still or slow-flowing waters. Most of the flying dragonflies can be observed between mid-May and mid-September.


 Larvenschlupf Großlibelle

The larva of a large dragonfly has climbed up a leaf and clung to it. In the following hours, the initially soft-skinned adult dragonfly hatches. Its body stretches and its exoskeleton hardens and the dragonfly larva's skin remains on the leaf.

"Emergence of a Dragonfly" by Rison Thumboor is licensed under CC BY-SA 4.0.


 BlaueFederlibelle Larveblaue Federlibelle

Left: Larva of a damselfly, the White-legged damselfly (Platycnemis pennipes), since the larva also hides in the bottom of the water body, they are often covered with mud when they crawl on land and appear grayer than underwater.
Right: A male of the White-legged damselfly

 "File:Platycnemis pennipes (Platycnemididae) (Blue Featherleg) - (larva - nymph), Elst (Gld), the Netherlands - 2.jpg" by  B. Schoenmakersat waarneming.nl is licensed under CC BY 3.0.

"Federlibelle (m)" by vobebis is marked with CC0 1.0.



 Prachlibelle imagos

Here are two imagos of the Beautiful demoiselle (Calopteryx virgo), on the left the male, on the right the female. The blue-winged damselfly can be found in and along some river courses of the Oesling, the Beautiful demoiselle prefers still or slow-flowing waters with many plants.

"File:Beautiful Demoiselle Calopteryx virgo male female.jpg" by Richard Bartz is licensed under CC BY-SA 2.5.

 N Libellen 1                            N Libellen 4

Typical shape of a larva and an imago of the group of true dragonflies (top)


N Libellen 2                                                          V Insekten 4

Typical shape of a larva and an imago of the group of damselflies (below).

Drawings from Kosmos Publishing House




Here you will find a simple illustrated identification guide for small animals that you can find in the water. A large part of the larval stages of various insects, but also crayfish such as the waterlouse are described. Also look for the notes of distinguishing characteristics or possibilities of confusion (black diamond).

The table is originally from GLOBE Swiss and has been modified and extended.


EN Bestimmungshilfe von Globe Makroinvertebraten



V Krebse 6Wasserassel1

The water louse (Asellus aquaticus), a commonly encountered species.

Photos: Kosmos Publishing House and GLOBE Swiss

Most crayfish species live in the sea, but there are also some representatives in fresh waters. Frequently encountered crayfish species in our waters are rather the small, often only up to 20 mm in size and with an articulated carapace (Peracarida). These include the water louse (Asselus aquaticus), which is found in slow-flowing and stagnant waters. It has no great demands on water quality and lives among foliage and dead plant debris. Aquatic isopods eat detritus and play an important role in decomposing foliage. Woodlice are often grayish brown, sometimes purple in color. Unlike the freshwater amphipod, it crawls over the ground and does not curl its body.

V Krebse 7  Flohkrebs

The freshwater amphipod (Gammarus pulex) lives as its name indicates in streams, there is also an amphibod species that lives more in lakes (Gammarus lacustris). The body is quite light and lies on its side in resting position and is usually curved. The amphipods colonize all types of water, but the oxygen and calcium content must not be too low. The name refers to the dynamic swimming movement of the amphipods. Freshwater amphipods also decompose dead plant material, but sometimes they eat mosquito larvae. They also provide an important food source for predatory fish.

Native decapods like the European crayfish (Astacus astacus) are almost non-existent,
they have almost all been replaced by the invasive
decapod species. See the Signal Crab or the
Camber crab.

"File:Astacus astacus in danger.jpg" by brian.gratwicke is licensed under CC BY 2.0


THE SURGERY (MOLLUSCA) - Mussels and snails

Bivalves and snails both form a shell in which they live, they have either a muscular adhesive foot (bivalves) or a foot with a creeping sole (snails) over which they move actively. As filter feeders, herbivores and detritus eaters, they colonize almost every type of water body and have no great demands on it. They are often easily transferred to other waters by, for example, waterbirds.

Mussels (Bivalvia)

The most common mussels found in our country belong to the group of freshwater mussels (Unionidae) and live mostly in and on the bottom of the water. They even move with their foot, although very slowly. Sometimes in shallow waters you can see their meter-long furrows they dug into the sand or mud while walking on it. The freshwater mussels play an important role in keeping the water clean, because they continuously filter suspended matter from the water. One large mussel filters about 40 liters of water in one hour.


 V Weichtiere 1

Typical shell shape of a freshwater mussel

Drawing from Kosmos Publishing House


The swollen river mussel (Unio tumidus ) is the sister species of the endangered thick shelled river mussel (Unio crassus). They differ only in size.

Foto: "Unio tumidus 2010" by G.-U. Tolkiehn is licensed under CC BY 3.0.

The shells all look very similar, the shell shape is more or less elongated oval and there are cones on both sides. The colorations are mostly dark. The thick shelled river mussel (Unio crassus) lives only in rivers and streams, it is dark colored and grows only up to 60 mm long. It can live over 30 years, twice as long as the average dog. It is highly endangered and is under strict European conservation law. Its sister species the swollen river mussel (Unio tumidus) is also found in lakes and calm flowing rivers. As well as the swan mussel (Anodonta cygnea), it grows up to 20 cm.
By the way, mussels form pearls only when large foreign bodies get into their shells.

Native zebra mussel or invasive quagga mussel?

The zebra mussel (Dreissena polymorpha) is easy to recognize, it has a yellowish green shell with brown waves or zigzag lines. The color contrast and patterning has given it its name. It inhabits rivers and lakes but actually originates from the Black Sea region. However, it has been part of our waters since 1820 and is therefore not considered invasive but an established species. Its sister species the quagga mussel (Dreissena rostriformis) is currently spreading as an invasive species (link to quagga mussel). It is difficult to tell the two apart, but the quagga mussel has a rounded upper edge and often lacks patterning.


"Dreissena polymorpha" by cohen is licensed under CC BY 4.0.

So different the zebra mussel can look, how the pattern is also depends on the environment.
Since the mussel is in close contact with all dissolved and suspended substances in the water, as well as
pollutants directly from the water, it is collected and examined by the Federal Environmental Specimen Bank
collected and examined.


Snails (Gastropoda)

 V Weichtiere 2Snails can be found almost everywhere, on land live the lung snails and in the water the gill snails or the freshwater lung snails. The freshwater lung snails were originally once land snails and then in their evolutionary history migrated back into the waters, they must regularly replenish their air supply at the water surface. Unlike land snails, the eyes of water snails are not at the ends of the antennae, but at the base of the antennae - the antennae are therefore "eyeless". Water snails are found in stagnant or very slow flowing water, i.e. in ponds, lakes or on wide river banks. There, they often crawl around near the shore on water plants, from whose leaves they eat off the algae coating. Or stones, which also have an algae coating whereby they can perfectly use their rasping or rubbing tongue. They are found in many types of water and do not have high demands on cleanliness.

Examples of freshwater air-breathing snails:

 Zwergposthörnchen Gyraulus Armiger crista

The Nautilus ramshorn (Gyraulus crista) is widespread and prefers densely vegetated small waters (ditches, ponds to lakes). It belongs to the freshwater lung snails. The shell is very flat and indented in a disc shape. The coloration varies from grayish white, almost transparent to dark horn colored. It is very small with a diameter of 2.8mm, but often occurs in groups and is therefore easy to spot.

„Gyraulus (Armiger) crista“ by Glodny is licensed under Public Domain self


A much larger snail is the great ramshorn (Planorbis corneus), its shell is up to 34 mm in diameter and olive to brown in color. It lives in larger waters in still waters or very slow flowing rivers.


"File:Planorbis corneus A MRKVICKA.JPG" by Alexander Mrkvicka is licensed under CC BY-SA 3.0.

Gill snails

The mud bithynia (Bithynia tentaculata) is one of the most common freshwater snails, in Luxembourg it is found in lakes and also in the lower reaches of major rivers such as the Moselle and Sûre. It is bioindicator for moderately to critically polluted waters, so it also occurs in brackish water.


The snail Bythinella dunkeri, inhabits clean springs and spring creeks of the low-calcareous low mountain ranges, especially in the north of Luxembourg. Often it occurs in the spring stream area, during dry periods, such as in summer, the spring snails retreat to the underground areas of the spring. In the colonized waters it can reach high settlement densities (up to 16,500 individuals per m²). It sits on dead leaves, wood, water plants and stones.


 Bithynia adult

"File:Bithynia tentaculata A MRKVICKA.JPG" by Alexander Mrkvicka is licensed under CC BY-SA 3.0.

Bithynia Eier









Offspring of Bythinella dunkeri: The female snail sticks a spawning line with about 20-40 eggs to a hard substrate like stones. The young hatch depending on the water temperature and live in 13-26°C warm water.

"Bithynia tentaculata eggs 10" by michal.manas is licensed under CC BY 2.0.



Bithynia Haus

Their shell is up to 11mm high and 7mm wide and yellowish transparent to reddish.


"Bithynia tentaculata_(I1775)_0241" by SERC Photos is licensed under CC BY 2.0.




Here you can see how small the Bythinella dunkeri is, they are found in clean and clear spring areas.

"Bythinella compressa" by Dieter Schmitt is licensed under CC BY-SA 3.0.



V Würmer 4


Leeches are worm-like animals with suckers at the ends of their bodies; they move by alternately sucking or releasing the suckers and sometimes curl up when disturbed or swim with their bodies extended. Leeches are insensitive to water pollution, they are therefore found in all waters and also brackish water.

Here are some exemplary sample species:

A species up to 10 cm in size is the common fish leech (Piscicola geometra). The common fish leech has only two requirements for the water body: The water body must be rich in plants and there must be fish in it on which it can suck blood. Sucking blood does not kill the fish, but it weakens them. Whether it is a river, a large lake or a tiny stream does not matter to the leech. The slender build and regular cross stripe pattern distinguishes the fish leech from other leeches and worms in the pond.



Probably the most common species in European waters is Erpobdella octoculata, it inhabits stagnant and flowing waters, even if they are polluted to some extent and polluted with nitrate. It grows to a size of 3-7 cm. This Rollegel has 8 eyes, four of which are located in the front, and 2 each on the two sides of the head. It does not suck blood like its other conspecifics, but devours its prey such as mosquito larvae or other mud tube worms directly by sucking them in. It also eats carrion and therefore plays an important role in the metabolic cycle of a water body. The dog fluke attaches its egg cocoons to the leaves of aquatic plants or under rocks, and one cocoon can contain up to 30 eggs. This species of leech can be used as a bioindicator due to its ability to survive in polluted waters. Levels of contamination can also be determined by the amount of pollutants in the tissues of E. octoculata.

The leech Alboglossiphonia heteroclita is a relatively small leech (max. 12 mm, pictured top center) and has been shown to be sensitive to oxygen depletion and phosphate loading in water bodies. It is found only in moderately polluted waters, but is not as sensitive to nitrate. It prefers to suck on water snails but also on other worms and insect larvae.



fish leech (Piscicola geometra) it is greenish brown patterned and up to . The slender physique and regular transverse stripe pattern distinguishes the Pisces leech from other leeches and worms in the pond.

"Piscicola geometra" by Rob Foster is licensed under CC BY 4.0.


The Erpobdella octoculata, grows to 3-7 cm in size. It has 8 eyes, four of which are located in the front, and 2 on each side of the head. A characteristic feature of the dog fluke is that every fifth abdominal ring is slightly lighter in color.

"Erpobdella octoculata" by s173 is licensed under CC BY 4.0.




V Würmer 3


Most annelids are ecologically important because they are considered very tolerant and are often found in large numbers in polluted streams or stillwaters. They live half buried in the mud at the bottom of a water body or among aquatic plants. Many species are light, brown or even reddish.


 Schlamm tubifex

"Tubifex" by Timothy Gerla is licensed under CC BY 4.0.

Species of Mud tube worms (Tubificinae) live in self-made tubes in soft sediment, i.e., in the mud or sand of flowing or standing waters. Typically, only the rear end of the worms peeks out of the sediment surface. They swirl oxygenated water and organic material by movement. Some species are blood red due to hemoglobin, e.g., Tubifex species. Mass reproduction occurs only in waters whose sediments have a high proportion of usable organic material (eutrophic). In unpolluted waters they tend to occur only sporadically. Some species are used for water quality assessment. The species Tubifex tubifex can grow up to 8 centimeters long.






Amphibians such as frogs and Salamanders (e.g. frogs and newts) are useful indicators of artificial pollution in a water body, such as from chemicals. They have permeable skin and absorb oxygen through it - but also dissolved toxins such as pesticides. When pesticides enters the water, populations shrink which should be alarming.

In addition, many amphibians are threatened with extinction, one reason besides road traffic is the spread of the deadly amphibian chytrid fungus.The exact origin of the fungus is still unclear, but this is referred to as an epidemic. It is clear that it spreads through water, for example, when people walk through various bodies of water with rubber boots. Dan they carry the fungus on the soles of their shoes possibly into waters that are not yet infected. Especially fire salamander populations in the Eifel region have shrunk considerably due to the fungus. It now occurs worldwide and also in many biodiversity hotspots; West Africa and Madagascar are the only chytrid-free regions in the world. The invasive bullfrog (Lithobates catesbeianus)



"Oh a frog!" But wait, there is a difference. There are toads (Bufonidae), tree frogs (Hylidae), and true frogs (Ranidae).Many frogs are not aquatic at all, but live most of the time on land in areas of high humidity. They come to pools, ponds, lakes, or large puddles only for mating and spawning in the spring. At night, the frogs go hunting for insects; they sometimes hibernate in burrows or densely packed at the bottom of bodies of water.


The European toad (Bufo bufo) is recognizable by its yellowish, reddish to dark brown upper surface with irregularly distributed warts (warts are a characteristic feature of toads). It bears knobby ear glands on its temples. Like most toads, it is nocturnal and a land dweller, migrating to a water source only to spawn. There it produces spawning strings with up to 7000 black eggs.

Hear the call of the European toad!

Bufo bufo Erdkröte          

"File:Bufo bufo (Common toad), Arnhem, the Netherlands.jpg"
by Bj.schoenmakers is marked with CC0 1.0.

Toad-spawn Mike-Krüger.jpg by MikeKrueger is licensed under CC BY-SA 3.0


The European tree frog (Hyla arborea) , is nocturnal and hides well camouflaged in bushes during the day, which is probably why few people get to see it often. The Tree Frog prefers to inhabit diverse landscapes with high water tables and an abundant supply of suitable spawning waters. These are ideally free of fish, in any case well sunlit and have shallow water zones as large as possible. In summer, the tree frog prefers wind-protected areas with high humidity, which can be, for example, hedges, blackberry bushes, forest edges in which many insects live.

Laubfrosch Hyla      Laubfrosch Hyla Blase

FelixReimann, CC BY-SA 3.0, via Wikimedia Commons

"European Tree Frog (Hyla arborea), Budy near Białowieża, Poland" by Frank.Vassen is licensed under CC BY 2.0.


The Edible frog (Pelophylax esculentus) belongs to the true frogs (Ranidae). It is probably the most common frog to see. It lives in sunny still waters, especially ponds and semi-natural ponds, where the frogs can sunbathe and look for insects sitting on the shore or on lily pads. The Edible frog has a peculiarity, it is not a biological species in the classical sense, but a hybrid, that is, a cross between two water frogs. Namely from the parent pair marsh frog (Pelophylax ridibundus) and pool frog (Pelophylax lessonae). Although it is a hybrid, it can produce healthy offspring due to genetic peculiarities.
The pool frog is green to light brown on the upper side with blackish brown or green spots and usually light green dorsal stripe. Males carry two sound bladders on the side of the head. In the spawning season April to May, the Edible frog lays spawning balls with about 300 eggs each.

Call of the pond frog     


 Teichfrosch Laich

"Frog Spawn" by twoody291 is licensed under CC BY 2.0



The Grass frog (Rana temporaria) also belongs to the true frogs and among them to the subgroup brown frogs (Rana). The upper side can be yellow, red or dark brown in color. It bears a long dark brown stripe on the temple. It lives on land and mostly in meadows, bogs, swamps or even moist, deciduous forests. There it can camouflage itself perfectly by its coloring. Spawning waters include a wide range of standing or slow-flowing waters. Preferred, however, are shallower, sunlit still waters such as small ponds and ponds (also garden ponds), which, however, may rarely dry out, or also cattle watering places.

 Grasfrosch Rana temporaria cropped

Richard Bartz, Munich aka Makro Freak Image:MFB.jpg, CC BY-SA 2.5 , via Wikimedia Commons

 Grasfrosch Rana frogspawn

Salimfadhley, CC BY-SA 3.0 , via Wikimedia Commons

Amphibians: Chordate (Chordata)

V Wirbeltiere 3V Wirbeltiere 4

Salamanders (like tailed amphibians) live in quiet ponds, ponds and lakes and hunt for prey there, unlike frogs they have an elongated body and no jumping legs, also they have a kind of tail fin with which they move. The larvae of newts living in water (only the larvae of frogs are called "tadpoles") usually have external gill tufts and develop the front extremities first. They feed exclusively as predators, unlike tadpoles. In the spring (February/March), the amphibians move to their spawning grounds, wrapping their eggs in leaves and sticking them there. Most newts are nocturnal and stay in their spawning waters from March to August. Spawning waters can be pools, ponds, ditches, or dredge ponds. Females are usually not as colorful and without crests. Therefore, they can be more easily confused with other species. But beware, the comb of the male attaches itself to the body of the newt on land and is then hardly recognizable.


 imm Wasser Lissotriton Vulgaris Teichmolch

Usually you can spot them if you sit quietly next to the water and watch, newts are very shy and camouflage themselves well between water plants.

"230516 Common Newt (Lissotriton vulgaris)" by pete. #hwcp is licensed under CC BY 2.0.

 Triton cristatus Lebenszyklus

Developmental stages of newts using Triturus cristatus as an example.

Special Collections of the University of Amsterdam, Public domain, via Wikimedia Commons


The European newt (Lissotriton vulgaris)

Size: up to 110 mm. Males and females of the pond newt look slightly different.

Male European newts: bear an upright wavy dorsal crest in the water and are yellow to olive brown in color on the upper side. The belly is orange to yellowish in the center and bears large dark spots (see photo).

Female European newts: Have a pale belly, with small dark spots. The upper side is yellowish to sandy brown. They do not have a dorsal crest and therefore can be more easily confused with another newt species, the Palmate newt (Lissotriton helveticus). Unlike the threaded newt, however, the throat is usually spotted as well, and another distinguishing feature from threaded newt females is the lack of yellow pads on the sole of the foot.

Teichmolch Larve

The tadpole of an European newt (Lissotriton vulgaris)

"Smooth Newt (Lissotriton vulgaris) larval stage" by gailhampshire is licensed under CC BY 2.0.

Teichmolch bauch

The abdomen of Lissotriton vulgaris is orange to yellowish in the center and bears large dark spots

"Male Smooth newt. Lissotriton vulgaris" by gailhampshire is licensed under CC BY 2.0.



Palmate newt (Lissotriton helveticus). The male newt has a conspicuous thread-like extension of the tail. The comb of the newt is smooth-edged and not serrated, as in the European newt or Northern crested newt. The strong webbing on the toes of the hind legs and the irregular small spots are also conspicuous.

James Lindsey at Ecology of Commanster, CC BY-SA 2.5, via Wikimedia Commons

 Kammmolchmaennchen    Triturus cristatus bauch Kammmolch

The belly of the Northern crested newt (Triturus cristatus) is yellow-orange, the spots on the belly side are larger than on the throat (difference from the pond newt). The males have a crest that stands up in the water. Another difference from the European newt (Lissotriton vulgaris) is that the crest is higher/larger, also it is interrupted shortly at the beginning of the tail (tail root) (see photo). Especially popular with great crested newts are fish-free waters with rich underwater vegetation.

up: Rainer Theuer., Public domain, via Wikimedia Commons

bottom: Magnefl, CC BY-SA 4.0 , via Wikimedia Commons



Many fish species in our flowing waters have returned due to the renaturation of the river courses. During renaturation, particular attention is paid to ensuring that rivers can be navigated, i.e. dams or other structures in the water are removed. Many fish, including the common nase (Chondrostoma nasus), migrate upstream in large schools during the spawning season, from March to May, or enter suitable tributary streams. Many carp species live in plant-rich and eutrophic waters, whereas schooling fish are more likely to be found in cool, oxygen-rich waters. There are also newer fish species that are spreading into native waters and have been classified as invasive such as the black bullhead (Ameiurus melas) or the stone moroko (Pseudorasbora parva).


Examples of some fish species in nutrient-rich (eutrophic) lakes:

Carp fish:

European carp (Cyprinus carpio)

Tench or doctor fish (Tinca tinca)

Examples of some fish species in rivers with nutrient-poor, oxygen-rich cool water:

Brown trout (Salmo trutta fario)

Common minnow (Phoxinus phoxinus)

Schneider (Alburnoides bipunctatus)


Other forms of animals


Flatworms (Plathelminthes), which are found in our waters, usually have dark colors such as brown, gray or black. Their body is flat and elongated, the head has two eyes and is triangular or arrow-shaped in some species. They feed mainly on live and dead small aquatic animals (e.g. small crustaceans, worms and insect larvae), first sliming the prey and then adding a digestive juice. The dissolving tissue is later sucked in.

Many planarians prefer cool, moving water. Thus, they are found in springs, streams, and surf zones of lakes. Most flatworms are sensitive to warmer water temperatures but tolerate light pollution of water bodies. The exception is the triangle-headed Dreieckskopfstrudelwurm (Dugesia gonocephala), which is found only in clear, clean alpine streams. Almost all flatworms are shy of light, so they are usually found on the underside of stones, branches or floating leaves.


Dreiecksstrudelwurm Dugesia gonocephala

"Dugesia gonocephala" by Branislav Tej is marked with CC0 1.0.



 Dugesia spec. has two subspecies that are easily confused with each other. Both have a triangular head and small protruding corners. However, the triangular Dreiecksstrudelwurm (Dugesia gonocephala) is found only in clean flowing waters. While Girardia tigrina (synonym: Dugesia tigrina) (neozoon from North America) also lives in slow flowing streams and rivers and is insensitive to temperature changes and water pollution. It was introduced from North America around 1931. It is also called tiger swirl worm because of its blotchy surface.

 Tiger Strudelwurm

Dugesia tigrina (Neozoon from North America)

Mike6271, Public domain, via Wikimedia Commons