Pond Life in the UK - the Larger Creatures
Created | Updated Feb 13, 2009
Pond Life in the UK
An Introduction to a Microcosm | The Larger Creatures | Exploring the Small World
Pond life can include many different animal life-forms and, as discussed in A45687342, much can be found at a microscopic level. But we're probably more familiar with the creatures we can see with the naked eye - perhaps the most prolific on Earth being the first example:
The insects are very well represented, though to a large extent only by their larvae. Most midges or mosquitoes are water-borne in the younger stages, and some are most unusual.
The common mosquito, Culex pipiens, is laid as a bottle-shaped egg in a larger 'raft' of eggs. The raft is slightly curved and of irregular shape. These rafts can often be seen floating in water butts and the like.
The larvae are up to about 8mm long with a tube or tail at one end. This is usually somewhere near the surface, as it is used to breathe through. At the other end is the head with several bristles protruding. The body is cylindrical and made up of several joined-together bulges.
There are quite a number of fairly similar species, one of which is only found in the puddles formed where the branches of a tree join the trunk.
Another species of interest is Chaoborus, otherwise known as the Phantom Midge. The larva is completely transparent, less than 1cm long, and prefers large open bodies of water. At one end is the head (a bit like the head of a dragon but with one big tooth and no jaw). And near each end are two bumps - each housing two gas bags which keep the creature afloat. It moves by tying its body in a knot, then releasing itself, and is quite an active hunter. Other species build tubes and live in mud; still others cling to rocks in streams.
Mayflies are very common around ponds. The adult has three fine hairs protruding from its rear, flies a little fitfully, and is supposed to live for only a day. There are quite a few species in the UK, the smallest of which is about 5mm long as an adult, going up to about 2cm. The mayfly is unique amongst all insects in having a second moult once adult.
The larvae feed mostly on very small creatures in the water, but, as they have feeble mouthparts, are not as actively predacious as most other insect larvae. They have seven pairs of external gills beside the tail and, like the adults, three hairs protruding from the rear. The larval stage generally lasts for up to a year, while the adult can last as long as two days - but most only a few hours.
There are three species of The Alder Fly, otherwise known as Sialis, resident in the UK. The body of the larva is cylindrical with seven pairs of protruding tubes which act as gills, much like the mayfly. The adult is distinct in that its wings are large and lace-like, and when at rest cover the body like a cape. The larvae are predacious, as is the adult.
Other relatives are the snake fly and lacewing - they all have the same distinctive wing pattern.
Stonefly, or Plecoptera, larvae are found mostly in flowing water. The body is clearly divided into head, thorax and abdomen. It has two tails as opposed to three, and no external gills. The legs are held characteristically out from the body in a crab-like fashion.
The adult stonefly is more often found clinging to rocks in running streams, rather than in ponds. Its wings fold over its back, but lie flat rather than tent-like. There are 34 species to be found in the UK.
The caddis fly, or Trichoptera, is a little unusual in the water world in that it usually builds a house and carries this about. The house is sometimes a leaf simply curled around, but sometimes the Caddis builds a web around its body and decorates it with sticks and other debris. In the extreme, several species build a cylinder of fitted-together pieces of sand, carefully chosen to be of the same colour and size, then glued together.
Others are naked to the world. In this group one species copies spiders and builds a net on the bottom of streams, catching debris and other insects as they flow past. The larva is cylindrical - usually pale white - and has rows of gills down each side. The adults are usually poor fliers, and provide easy prey to insectivores.
The china mark moth is entirely aquatic in its pre-adult stages. Its presence is often first noticed by cut-outs on the edges of water lilies. The larvae make a two-sided pouch from these cases and use them as a home. Their food is plant matter.
The adults are called china mark moths because of the markings on their wings, supposedly resembling the marks made on china.
Dragonflies & Damselflies
There are 64 species of dragonfly and damselfly, Odonata, in the UK. The largest, Anax imperator, can grow up to 70 - 80mm in length, and they truly are creatures of science fiction. A major feature of dragonflies is their eyes. They have the largest number of omatidia (lenses) of any insect, but despite this visual acuity their eyes are designed to be sensitive to movement and do not focus well.
Dragonflies can be caught by hand if the hand moves slowly enough. They also have a reasonably good memory (for an insect). But it is possible to stalk them; sooner or later your slow movements just become part of the background.
Dragonfly larvae are known as 'nymphs'. The nymphs of the larger dragonflies live in water for up to three years. When they are ready to emerge, the nearest plant stem is laboriously climbed. Their back, in between the wings, splits and out climbs a pale-looking dragonfly. The wings slowly unfurl and gradually the dragonfly's colour emerges. If it is disturbed during this process, however, it can drop into the water and drown.
With the dragonfly staying absolutely motionless for extended periods of time, their jaws will suddenly shoot out to capture a passing creature. The jaws are mounted on a hinge under the head; perhaps it would be more accurate to describe the jaws as a mask, as the affair is really independent of the mouth. If disturbed, the abdomen can contract to shoot the creature forward and out of harms way - in truth, they have jet propulsion.
There are two main body shapes in the large dragonfly world: the darter shape, which is essentially broad-bodied, and the hawker, which is the better known needle-like shape. Of the darter shape, the largest is Libelula depressa. This dragonfly is probably the most acrobatic being, able to fly backwards and upside down.
Of the smaller and less agile dragonflies, there are two main types: the larger 'demoiselles', represented in the UK by Agrion splendens and Agrion virgo, and the more numerous, smaller damselflies. The demoiselles are very striking. The male of splendens has a blue patch on its otherwise clear wing; the female is just brown. With the virgo, the male has blue (or purple) wings and the female is again brown.
The damselfly is a much daintier creature, with a matchstick-thin body. Usually a striking colour - reds, golds, blues and more - there are up to 36 species present in the UK.
The larvae of the damselfly are quite different to the dragonfly nymph. The body is slimmer and has external gills on the tail in the form of three small vertical plates. It also has the capacity to 'inhale' water, but cannot (as in the dragonflies) release it as a jet. When swimming, it moves its body from side to side in a flipper-like motion. Like dragonfly larvae, it has a 'mask' which it ejects from the face to grasp prey.
The Syrphids are truly amazing creatures. Often seen in the summer, their wings are a complete blur, and they hang completely still in the air. This impressive feat is done by male hoverflies to attract females. These animals move so quickly as to be almost invisible; it's as if they just disappear between places.
The most common species mimic flies and bees, but they are let down by the eyes - which are larger and more wrap-around than the creatures they are trying to copy. Their eyes are probably the largest in relationship to body size of any insect.
Their larvae are the rat-tailed maggots commonly seen in farmyards. They have the distinction of being able to live in water so foul as to be nearly completely deficient in oxygen. Their respiration takes place through their 'tails', which penetrate the surface. These are made up of three segments, and are telescopic.
The most common example of these interesting creatures are tiny bright-red velvet 'cushions' busily scrambling up the walls of canals or horse troughs on a warm sunny day. Water mites attain a maximum size in the region of 5mm. Their food is the fluids of other insects, or plant life.
Among the most striking of pond creatures, these beetles are mainly black with similar body shapes. They range in size from 3mm to 40mm, like the great silver diving beetle, or Hydrophilus piceus. This particular beetle has become rare, because in the 1930s it was much sought after as an aquarium pet and virtually wiped out.
The adult is entirely omnivorous, munching quite happily on a piece of pondweed as if it is chewing a piece of meat. Unique to this species are the two horns which project from the front of the thorax and are used as breathing trumpets. Most water beetles store air under the wing covers, and refresh it by simply sticking their bum above the surface. This beetle hangs below the surface with just its two horns piercing through, so it can quite easily drown if caught in a tangle of weed. The larvae are entirely predacious, feeding mostly on water snails.
Next in size is the biggest representative of the Dytiscidae, the great diving beetle. This has got to be one of the most voraciously carnivorous of all water beetles in the UK. The adults are about 27 - 35mm long, while the larvae grow up to 60mm.
The adult sexes are easily distinguished from one another. The male has ridged wing cases and clasping pads on the ends of its legs. The female is much more sophisticated, with smooth wing cases.
The larva is a mean eating machine. It digests its prey by piercing the body with sickle-like jaws, injecting digestive fluid and ingesting the resulting mess. While some diving beetles will live quite happily with other water creatures in a fish tank, this monster must be kept on its own.
The Dytiscids are quite a large family with several smaller representatives that are easily recognisable by their shape and movements, such as the Whirlygig Beetle. This amazing creature is probably the most prominent of our water beetles, in that its natural habitat is the surface; it can be seen swimming in circles rapidly.
Its eyes are probably unique in being divided into two, the upper for viewing above water and the lower for underwater. It is predacious, but eats dead creatures as happily as live ones. It is quite small, though - being no longer than 7mm. The larvae are also busily predacious, and a little unusual with long projections on each body segment.
The term 'bugs' is often used to describe any small creature or insect, but the true bugs are distinct from ordinary insects in that they all suck fluids.
Most commonly found in water, these range from Ranatra lineris, or the water stick-insect, which grows to just over 50mm; to Nepa cinerea, the water scorpion, which is just a little smaller; and the tiny Hydrometra aquatica, or water measurer, coming in at around 6mm in length with a tiny stick-thin body.
The water stick-insect has a long cylindrical body with three pairs of long tapering legs, the first pair of which is modified into claspers. The wings are tightly furled around the body, and quite often leave the water.
The body shape of the water scorpion is a little like a very thin violin, with three pairs of legs, and again the first pair are modified to form claspers. Despite the scorpion moniker, they do not have a sting on their tail. They have that name because the siphon (snorkel) on their tail gives them a scorpion-like appearance. These creatures feed by literally ramming the food into their 'beak' and claspers, and holding on.
Overall, the Hemiptera family is sizable, with probably the largest of all water insects (12cm-plus) as one of its members - the scarily nicknamed 'Toe Biter'. This particular insect is also regarded as a delicacy, and eaten widely by humans throughout Asia.
Other Water Bugs
One of the most common water bugs is the pond skater, Gerris najas. This is the most prominent of our surface tension-using water bugs. Their food is pretty much anything they can get, including carrion. They can often be seen feeding on the bodies of such creatures as crane flies which have fallen into the water. Their habitat being the surface layer of water, their movements are a bit like someone walking on a giant plastic bag.
Another, which may be seen looking up at Gerris, is the water boatman, Notonecta. This is an ace predator whose natural habitat is under the surface. Probably the fastest of all our water bugs, its very streamlined body is propelled by oar-like feet - they literally row themselves about. The body is so streamlined that colour is the best way of differentiating body parts. Strangely enough, its normal position is upside down; apparently this is not determined by gravity, but by light.
There are two classes of mollusc represented in freshwater. One is the Gastropoda (stomachfoot), or Univalves (meaning one shell). The other is the Bivalvia, meaning two shells.
There are as many as 36 different gastropod species to be found in the UK. They are again divided into two main groups: the Pulmonata (lung breathers), and the Prosobranchia (gill breathers).
The Pulmonata don't have gills. Instead, they are able to make a cavity within their body in which they trap air. The opening from this can be seen as a small round structure on the right-hand side of the snail when on the surface. It has some other interesting properties, too. The lung can be used as a buoyancy aid, or the air can be expelled, dropping the snail to the bottom at speed. In addition, any part of the body coming in contact with water can act as a gill, to a limited extent. So the snail is not totally dependant on contact with the atmosphere.
The Prosobranchia, as well as having gills, is further distinguished by a horny or chalky plate which it uses to cover the opening of the shell. This is known as an operculum, and thus the group is known as the operculates. Mainly found in well-oxygenated water, the two most common operculates of any size are the freshwater winkles Vivaporous vivaporous and Vivaporous fasciatus. They can grow up to 35mm and the shells are usually a greenish-brown colour with three dark-brown strands running around each whorl. Their name implies live birth, and indeed their young are produced fully able to feed and look after themselves. The eggs are hatched inside the mantle, with about 50 produced at a time.
Another interesting group are the Valvata, of which there are three species. The foot is divided into two, with a 'snout' between the two tentacles. A gill and another appendage used in respiration protrude from the shell as the creature moves about. While most freshwater gastropods are of either sex, this group are hermaphrodite.
The biggest pond snail, Lymnaea stagnalis, grows up to 55mm in length. Its diet is not restricted to vegetable matter like most other snails, and it will eat carrion. It has even been seen attacking fish!
Gastropods have an unusual device for feeding; it's in the mouth and comprises a strip in which are embedded rows of teeth. This is used to rasp food from whatever source required, and is in fact a very efficient feeding apparatus, with some unusual adaptations and functions within the class.
One member of this family, Lymnaea truncatula, is the intermediate host for the liver fluke, which not only affects ruminants1 but can affect humans. Most water snails lay their eggs in a gelatinous group, either on the underside of leaves or on stones or other similar surfaces.
One of the most common species to be found is the ramshorn snail. There are 14 species, and they range in size from over 25mm in breadth (the great ramshorn) to 3mm in breadth (nautilus ramshorn). These snails are unusual molluscs, in that their blood contains haemoglobin. This is more efficient at absorbing oxygen than the cyanoglobin of other molluscs, explaining their infrequent contact with the surface.
Another noteworthy aspect of the ramshorns is the occasional appearance of a bright-red individual. This is caused by albinism which leaves the shell clear. There are also two species of freshwater limpet common to UK ponds.
There are 26 species present in UK freshwater habitats. These include the larger mussels, the smaller orb shell, pea shell cockles, and the rather unusual zebra mussel.
The most interesting and common of the mussels is the large swan mussel, Anodonta cygnaea. Specimens have been found up to 230mm in length, but are more commonly in the region of 130mm. Their main habitat is a muddy substratum in water with little current, and they can live for up to 30 years. Their food is pretty much anything organic floating in the water.
They are quite mobile, pulling themselves along by pushing the foot under the mud surface and contracting and expanding the muscle inside, producing the motion required for propulsion. It's a grand sight to see one of these very quiet and unpretentious creatures cruising along just minding its own business, doing its stuff. Their use in a freshwater aquarium is a little limited, but they function as water cleaners, removing bacteria and other substances.
Swan mussels produce larvae, glochidia, once a year. They look a little like miniature cockles, but with a tooth on each valve. The larvae are equipped with a thread which is sticky, the byssus. When the mussel is maturing, these threads are expelled from the shell - usually when a fish is passing. The larvae then affix themselves, by means of this sticky thread, to the side of the fish. A cyst, in which the mollusc develops, forms on the fish. The most used fish in the UK is the stickleback. On the continent, however, the Bitterling lays its eggs in the mussel, and is the recipient of clouds of glochidia. So there is a mutual exchange of young, which is pretty rare in the pond world.
In general, the smaller bivalves are hermaphrodites, while the larger ones have distinct sexes. The pearl mussel, Unio margaritifer, found mainly in the north of England and Ireland is up to 160mm in length, and blackish in colour. In Roman times, it formed part of an important fishery, freshwater pearls being of great value. A fishery on the Tay produced, between 1761 - 1764, £10,000-worth of pearls for the London market.
The zebra mussel is a handsome creature whose shell is marked by transverse brown or yellow bands. It grows up to 50mm in length and, like its sea relatives, attaches itself to substrata by a byssus. It has a useful feature in that it removes heavy metals and other pollutants from water. It has been considered as a potential first stage cleaner, but it has a disadvantage in its habit of blocking outfalls by crowding together in the entrances of pipes and outlets. This bivalve is not a native, having first appeared in the 1820s.
Spiders in ponds are often represented by Argyoneta aquatica. This amazing creature makes a diving bell out of silk and spends its time underwater. It eats pretty much anything that it can get, its main prey being various mosquito larvae. When it is moving around, the air it breathes is trapped in fine hairs under its abdomen.
In terms of looks, there is not much to distinguish this spider from any other. But it is the only representative of the ordinary house spider that has taken to the water in Europe.
The Hirudinea comes in many different sizes, but the largest is the medicinal leech. Some 200mm long when fully grown, it has actually become quite rare in the wild. This animal is a true blood sucker, though most of the other leeches in the UK are not. The horse leech, for example, simply eats snails and other molluscs.
The next Entry, A45901712, introduces us to some more of the larger animals to be found in ponds. It then explains how to find and look after the various creatures already discussed - thus offering so much more for both the curious (and scientific) mind.