A. Invertebrates (Other)
More extensive information on invertebrates can be found in a separate blog post.
B. Earthworms (LUMBRICIDAE)
Nearly all British earthworms belong to this large northern hemisphere family. Having retractile body structures helps them while burrowing. Species of this family have four pairs of setae per segment, which have diagnostic usefulness.
C. Black-headed Worm (Aporrectodea longa)
This worm is anecic so makes vertical burrows. Its pinky-red body is very dark, almost black, at the head end and paler towards the tail.
Our local representatives of the huge group of Annelid worms are easily distinguished and among the most recognisable of our invertebrates. Earthworm bodies are constructed of many ridged segments (called annuli) covered in minute hairs (setae) like small bristles, with which they burrow and move. They have no lungs, but breathe through the skin. To keep the skin moist they secrete mucus. Earthworms are hermaphrodite, but two worms are needed for mating as they are not self-fertilising. Along the body is the clitellum, or saddle, which contains both male and female sex organs. A linear area of the clitellum is called the Tubercula pubertatis (TP), and this indicates that the individual is a sub-adult. If there is no clitellum, and therefore no TP, the individual is a juvenile. About half-way between the head and the TP will be the ‘male pore’, if there is one.
Earthworms are omnivores, eating plant material and small invertebrates. They occur in most soils, unless they are extremely acidic or waterlogged, and need to maintain moisture levels, so tend to lie dormant if conditions are very cold or dry. They are active at night, consuming soil and extracting food from it. The mouth is in the first segment, and the unwanted soil debris is passed through the body. Their burrowing aerates the soil, and their feeding helps distribute minerals and organic matter, so they are vital to soil health. In the UK we have one species in the family Acanthodrilidae, one species in the family Sparganophilidae, and 28 species in the family Lumbricidae.
Four common lifestyles are recognised amongst British earthworms. Compost earthworms seek warm, moist rotting vegetation, such as garden compost heaps. They are often bright red in colour and have striped markings. Anecic earthworms make permanent vertical burrows in soil, and drag leaves down into them to feed on. They make casts on the surface, and some make piles of casts (middens) round the burrow entrance. They are usually darkly coloured at the head end, red or brown, with paler tails. Endogeic earthworms live in and feed on soil, and make horizontal burrows. They are often pale coloured, grey, pink, green or blue. Epigeic earthworms live on the surface in leaf litter, and are often bright red but do not have striped markings.