Invertebrates
Some of the invertebrates that can be found in and around the rivers and streams:
Mayfly
There are many types of mayfly that inhabit different types of rivers, streams and even ponds. The majority are very sensitive to pollution. They generally feed on algae or detritus on the river bed as nymphs, before emerging from the water to become winged adults. These can be seen dancing above the water in clouds. Mayflies can easily be distinguished by there three tails, but come in different shapes, sizes and colours.
Stoneflies
There are over 30 species of Stonefly in the UK. They like the mayfly feed on algae and detritus but there are also several carnivore species that feed on other stonefly and invertebrates. They are in their nymph stage in the water, but emerge as winged adults. However they are not confident fliers and you are more likely to find them on your clothing than see them flying.
Cased and Caseless Caddis
Caddis flies are related to moths and Butterflies, but spend there nymph stage in water, where they feed on algae, detritus, other invertebrates and even fish eggs. There are two major families, the cased caddis, who construct a “case” that covers there body and they can take refuge in, and a caseless caddis. The cased caddis make their cases from sand gravel, vegetation, pieces of shell and bind it together.
Gammarus
The gammarus or Freshwater shrimp does not go through any larval stage, it hatches as a small shrimp and remains in that form, but grows larger. They have a curved back and a flattened body, with seven pairs of legs. They feed on detritus – dead or decaying plant or animal matter. They can breed twice a year an as a result can grow large populations very quickly. They are considered a very important part of fish diets where they are found.
Damsel Flies
The Damselfly is of the same order as the Dragon fly, but can be distinguished quite easily in the adult stage when they are perched on vegetation. They hold their wings vertically parallel to there bodies. Where as the Dragon Flies hold their wings perpendicular to their bodies and in the horizontal plane. The females lay there eggs in water, at the verges or in aquatic weed, these then hatch into an aquatic larval stage. The nymphs are often mistaken as mayfly as they have three tails, however they have large flattened tails which differ greatly from mayflies. The nymphs feed on daphnia and other small aquatic micro organisms. After several moults they hatch as adults. The Adults feed on flies and other small insects.
Dragon Flies
Dragonflies are large flying insects The adults feed on other flying insects and can live for upto four months. In this time they will lay eggs on or in water, often in submerged or floating plants. The nymphs hatch out and can live for up to 5 years in the nymphal stage (depending on species). The nymphs are predatory using extendable jaws to catch their prey. They will also bite predators (including humans) if threatened.
Snails, Limpets & Bi valves
There are a range of freshwater molluscs that can be found in our river and streams. In the Ribble there is no records of the Freshwater Pearl Mussel. However we do have Swan mussels and it is likely there are other Bi valves. The Swan mussel has two hinged shells and a soft body. They have a stong foot which they can use to attached themselves to the river bed or burrow into the substrate. They are filter feeders, most species feed on diatoms, algae, bacteria and organic matter. The mussels keep their eggs within the shells over winter until they hatch, where the larvae are then released in the spring. The larvae then attach them selves to fish and suck blood for a period before dropping to the river bed and becoming filter feeders.
There are a number of different freshwater snails in the UK. They generally required non acidic waters as calcium is required for their shell. The move using a mat of mucus and a rippling action using their ripple muscle which the produce. They are omnivorous eating plants and algae. The reproduce by laying a mass of eggs in a Jelly like substance on vegetation.
Limpets are small creatures with a single shell. They stick to stones and substrate scraping off Algae.
Hog Louse
The Hog louse resembles an aquatic wood louse. It is from the order crustacean. They live in ponds or the margins of slow moving streams. Feeding on dead and decaying matter. They scuttle rather than swim. They are adapted to living in low oxygen environments and as a results are moderately pollution tolerant.
White clawed crayfish
The white clawed crayfish is the largest freshwater invertebrate, and the only native crayfish in the UK. Crayfish can live for upto 10 years, and reach sexual maturity after 3 or 4 years. Breeding occurs in early winter and the female carries her eggs over the winter until they hatch in spring. The Juveniles remain with the female until the second stage of development in the summer when they become independent. The White clawed Crayfish is omnivorous, however it is mainly predatory, feeding on invertebrates, fish and dead or decaying matter. Leaves may also be an important food source. They are very sensitive to pollution and require clean oxygenated water preferably alkali.