Woodlice are not the most exciting creatures to be found at St Nicholas Fields, but they are an important part of the reserve’s fauna and appropriately are very good recyclers! It is well-known that around the country woodlice are called by many different and sometimes amusing names like Roly-Poly, Billy-button, Pea Bug, Chisel Bob, Chuckywig, Tiddy Hog and Monkey-peas. There are 37 species of woodlouse in Britain and Ireland but only a few of these are commonly seen; the rest are specialists or found in rarer habitats. At St Nicks five of the seven commonest species are found regularly, some in large numbers, by looking under decaying logs or fallen stones. In order of abundance these are Common Shiny Oniscus asellus, Common Pygmy Trichoniscus pusillus, Common Rough Porcellio scaber, Common Striped Philoscia muscorum and Common Pill Armadillium vulgare. Another species, Rosy Woodlouse Androniscus dentiger, has been seen only once but is undoubtedly present in larger numbers. The scientific name Porcellio scaber means ‘rough little pig’.
Both Pygmy and Rosy are very small (approx 5mm) compared with their three-times larger cousins. The equally small (and blind) white-coloured Ant Woodlouse Platyarthrus hoffmannseggi should also be present in some of the many ants’ nests on the reserve but has not been found yet. In Ireland it appears that the Rosy Woodlouse has Protestant leanings. Protestant cemeteries, unlike Catholic ones, once used Ox-blood mortar for gravestone cement which is particularly attractive to Androniscus dentiger.
Woodlice are crustaceans, relatives of lobsters, shrimps and crabs. Most crustaceans are aquatic and woodlice evolved from sea creatures via the seashore. Many of the scarcer British woodlice species do have a more coastal distribution. Within the crustaceae woodlice belong to the genus Isopoda, meaning ‘equal legs’, of which they have seven pairs. Their soft bodies have a hard outer case (exoskeleton) made largely of calcium carbonate. In order to grow, woodlice need to shed their case from time to time. They do this in two stages – their rear half is shed first (and eaten in order to recycle the calcium) and then the front half a couple of days later. Occasionally uneaten half-cases can be found. Woodlice mature in a year or less, and can live for 2 or even 3 years. Mating takes place mostly at night, usually between March and September. After courtship the male transfers his sperm into the female’s genital openings. The eggs take one to two months to hatch and are then transferred to the female’s brood pouch (marsupium) where the young grow until ready to crawl out to live an independent life. They undergo several moults until fully mature, and sometimes more after that. Females generally have one brood per year. Woodlouse food comprises mainly dying or dead plant material and they rarely attack living plants – so are no real threat to the gardener. Indeed they are the gardener’s friend, speeding-up decomposition and recycling dead plant material, returning nutrients essential for plant growth to the soil. Woodlice have few predators. Centipedes are responsible for about 40% of woodlouse predation, and there are two spiders of the genus Dysdera which are equipped with large fangs to penetrate a woodlouse shell.