Woodlice are amazing and often much maligned little animals that are well worth a second look. There are 3500 species of Woodlice in the world about 35 or 1% of these live in the UK. Though many of these are small and difficult to find, there are few larger species that are regularly found around buildings, see key below.
The common species are abundant in most habitats, and are easy to keep in margarine containers as they are incapable of climbing up the sides, some damp soil on the bottom and some house-hold vegetable scraps added occasionally and you have some great pets. Keep the soil damp but not too wet as excess moisture can kill Woodlice as easily as too little. Though the Woodlice will feed on the scraps that you put in they will also feed on their own faeces, this is quite natural, what they are actually eating is the fungi and bacteria that are living on the faeces. Some species mostly of the genera Armadillidium, commonly called Pill Bugs, are capable of rolling themselves up in a ball, this is a defence against desiccation as well as against predators such as shrews which find it much harder to bite a ball than an unrolled Woodlice.
If you find a dead woodlouse or cool one down in the fridge so that you can count the legs you will find that it has fourteen, seven on each side, from this you can realise that woodlice are not insects. They are Arthropods though, and share with Insects, Arachnids (Spiders and Scorpions etc) and Myriapods (Millipedes and Centipedes) a hard exoskeleton and jointed limbs; they are in fact members of the Subphyllum Crustacea, and therefore more related to crabs and prawns than to other terrestrial arthropods. Nearly all the Arthropods that live in the see are Crustaceans but Woodlice, and a few Amphipods, are the only Crustaceans to live on land with any great success.
Woodlice have endeared themselves to many peoples hearts in the past and there are numerous common names for those species which frequent human habitation, such as Bibble bugs, Cheesy bugs, Cud-worms (a reference to their use by farmers in the past to promote restoration of the cud) Coffin-cutters, Roly Poly, Monkey peas, Penny pigs, Sink-lice, Slaters, Sowbugs and Tiggyhogs. Though not everyone has liked them, in some parts of Britain in the past their presence in a house has been considered as unlucky and any food they walked over as poisoned. In other places they have been considered a remedy for stomach upsets and diseases of the liver when eaten live, their cuticle contains a lot of calcium carbonate so it is possible eating them may help cure acid stomach. Woodlice like most Crustaceans are quite edible and Vincent M. Holt in his book "Why not eat Insects" maintains that for making a seafood sauce woodlice are superior to prawns.
When a Woodlice is born it only has 6 pairs of legs, and is very vulnerable to desiccation (drying out) for the first part of its life it lives in a brood pouch underneath its mother, this pouch is composed of plates on the underside of segments 2-5, and is called a 'marsupium' and is grown especially by pregnant females for this purpose, at this age a young woodlouse is called a ‘manca'. After its first moult it gains its 7th pair of legs and leaves the marsupium. Like insects and all other arthropods growth can only occur at times of moult, but unlike insects Woodlice only shed half their skin at a time. When approaching the time to moult a Woodlice stops eating for a few days, then its skin splits around its middle and it sheds the back half of its skin, and then a few days later it sheds the front half, woodlice often eat their shed skin. The Woodlouse is very vulnerable during this time, and often seek a spot away from its fellows for the duration of its shedding, in fact some species, though not any British ones build themselves a cocoon to hide in while they shed their skins, In cultures a certain amount of cannibalism of shedding individuals may occur, particularly if the container is crowded. In nature many Woodlice die while they are still young and the older they get the more chance there is of them surviving to breed. Most of the larger species do not breed until they are at least 2 years old. Nearly all Woodlice are herbivores and many feed on dead and rotting vegetation, or the microbial flora that infests such material. Ligia oceanica (Common Sea Slater) is the largest species in Britain, up to 30 mms long, it lives only on the seashore and feeds mainly on the brown seaweed Fucus vesiculosus, while Porcellio scaber a common woodland species likes to feed on tree bark but will eat many other things. There are some carnivorous Woodlice, though not in Britain, in the genus Tylos , such as Tylos latreillei a Mediterranean species which lives on the seashore and feeds nocturnally on Sandhoppers.
Philoscia muscorum lives almost entirely on rotting leaves and occupies a similar habitat in both summer and winter, however other species such as Trichoniscus pusillus (Common Pygmy Woodlouse) which share the leaf litter with it during the winter change their habitat during the summer and live almost entirely on and in rotting wood, while Porcellio scaber which lives at the bases of trees during the winter moves higher up into the trees in summer. Not all Woodlice live in woods or Grasslands, Hemilepistus reaumuri lives in arid areas of North Africa and the Middle East where it survives in small family groups in holes dug in the ground these are 5-6 cms wide and can be over 30 CMS deep, digging is stimulated by high temperatures, over 35 C so if the bottom of the hole gets too hot they dig it a bit deeper. Even stranger than this are Platyarthrus hoffmannseggi (Ant Woodlouse) a blind, eyeless white woodlice found in Britain and Europe and Trichoniscus commensalis a pale coloured but still eyed species from New Zealand, both of these live primarily in ant nests feeding on ant droppings and fungi.
Mating occurs at night, and is therefore hard to see. The male climbs onto a receptive female, licks her head and drums on her back with his legs for about five minutes. He then shifts to a diagonal position on the females back and passes sperm to her left side genital opening from his right hand stylets. He then changes his position to the opposite diagonal and deposits sperm in her right hand genital opening from his left hand stylet. Sperm transfer takes about 5 minutes for each side. In some species such as Philoscia muscorum and Armadillidium vulgare breeding is synchronised within a colony so that all breed at the same time. Most species have one brood per year in Britain, though some such as P. muscorum have two in the South. The exception to this is the small triploid (having three sets of chromosomes) Trichoniscus pusillus which has two broods all over Britain. The number of eggs produced by a female of any given species increases with an increase in the size of the female, one female Armadillidium vulgare is recorded as having had a brood of 267 young. The eggs take from 3 to 9 weeks to hatch and spend from 3 to 9 nine days in the brood pouch.
Though many spiders find Woodlice distasteful, a few species will eat them i.e. Tegenaria gigantea and T. domestica, while some species like Dysdera crocata and D. erythrina have jaws specially developed to deal with Woodlice and live almost entirely on them. Armadillidium klugii from Dalmatia is a spider mimic and looks like the poisonous Laterodectes mactans especially when young. The only parasites of Woodlice in Britain are 7 flies of the family Rhinophorinae, Porcellio scaber is the most heavily parasitised, with 14% of those checked by Dr S.L.Sutton being attacked by 6 of the 7 species; 68% of these were attacked by Parafeburia maculata, 17% by Styloneuria discrepans, 9% by Melanophora roralis, 3.7% by Rhinophora lepida, 1.6% of Frauenfeldia rubricosa and 0.08% by Phyto melanocephala. Oniscus asellus is attacked by Parafeburia maculata and Styloneuria discrepans though not as heavily as P. scaber, less than 1% of those checked were parasitised. Armadillidium vulgare is also attacked by Phyto melanocephala while Trachelipus rathkei is attacked by Stevenia atramentaria. None of the other 7 species of Woodlice he checked had any parasitised individuals at all. Woodlice are also consumed readily by many small mammals such as shrews, which may easily consume over 100 per day if they can find them, as well as by many small birds.
To start this experiment you will need several petri-dishes with two pieces of filter paper in the bottom of them, in half of them the filter paper should be dry and in the others it should be thoroughly damp. You will also need a number Woodlice of each species you wish to test keep one third of them in a container that is absolutely soaking in water so that the Woodlice almost have to swim, one third in a container that is completely dry and one third in a container that has a damp substrate similar to that which you would keep them in normally (see above), for about half an hour. Then put one Woodlouse from each preliminary condition into one of each of the petri-dishes described first. Put the Woodlouse in the centre and then put the lid on and use a marker pen to record the Woodlouse's position every 15 seconds for about ten minutes. You do not need to do all the different combinations at the same time as long as your preparation is the same each time. After ten minutes let the Woodlouse go back to its normal home and work out both the total distance covered by the woodlouse, and the number of times the Woodlouse made a turn of more than 90 degrees. You can divide the total distance in millimetres by the number of turns greater than 90 degrees to get an activity number if you like. If you have more time try comparing not only different species but also individuals within a species and one individuals responses on a series of days to see if it remains constant. Do the Woodlice respond differently to the different treatments.
For this you will need a fish tank or something similar about 45 to 60 cms long by 20 to 30 cms wide, the bigger the better, with a centimetre or so of damp soil on the bottom and four identical shelters. Place the shelters at random in the tank, spread some food around the tank bottom and then place a Woodlouse under one of the shelters, is it under the same one the next day. Record its movements for a week, does it use one more often than the others. You can now try the experiment with four Woodlice, mark each one with a different colour of paint and record their movements for a week, now try it with four of each colour under each shelter. Do the Woodlice in groups respond differently to the individual one. You can run this experiment for as long as the paint allows you to tell who is who if you like. As an extension of this experiment you could set up shelters for woodlice in some open ground, a flat piece of 3-ply about 20 cms square with 4 pieces of timber 20 cms long, and 2 cms by 2 cms square on all four edges to hold it off the ground will do fine. Leave them outside for a week, then mark all the woodlice under each shelter use a different colour for each shelter, and check them each day after that for two weeks or until the paint wears off recording how many of each colour are under each shelter.
2a] Specimen has rows of tubercles (goose bumps) on each of the plates that make up the top surface of its
body, generally grey but often reddish, brownish or pale often with white spots .
Porcellio scaber (Common Rough Woodlouse)
2b] Specimen has no raised bumps on its back and is shinier..................3
3a] Specimen has a very clear darker line down its back, head generally the same darker colour as the central
stripe, runs very fast, commonly found in hedgerows and rough grassland, up to 11mm
Philoscia muscorum (Common Striped Woodlouse)
(Generally shiny and has green yellow, red and purplish forms)
3b] Specimen is generally greyish with splotchy white markings and sometimes an indistinct line along its back
Oniscus asellus (Common Shiny Woodlouse)
(Is larger than P. muscorum when full grown, up to 16mm and prefers damper habitats)
4a] Antennae not easily visible outside of rolled up body.
(Probably A. vulgare (Common Pill Woodlouse), there are other species found around buildings but
distinguishing them is difficult for the beginner, see below)
4b] Antennae easily visible outside of rolled up body ...............................5
5a] Specimen has two small but obvious tails (Uropod, exopodites) extending beyond the end of the body,
and has 5 pairs of lungs** on the underside .
Cylisticus convexus (False Pill Woodlouse)
5b] Specimen does not have obvious tails as above, often with a row or two of mainly darker spots on the
sides of the body, has only 2 pairs of lungs**, on the underside.
Armadillidium nasatum (Southern Pill Woodlouse)
(only in Wales and England South of Hull, commonly found in garden centres)
** A Woodlouse's lungs are visible as flat patches of white on the pleopods, these occur at the back end of the animal, after the legs when viewed upside-down, See fig 1.
If specimen is not one of these, or you are unsure and want to know more consult "A key to the Woodlice of Britain and Ireland" an Aidgap Key written by Stephen Hopkin. This can be obtained for about £5:00 from :- FSC Publications, Field Studies Council, Montford Bridge, Shrewsbury SY4 1HW
Taxonomy :- Order Arthropoda, Class Crustacea, Order Isopoda, Suborder Oniscidea.
Julie's Wonderful Woodlice Page Loads of info!!
Woodlice in N. Z.
Kates Garden, Minibeasts, Woodlice
An experiment on woodlice and moisture
The Woodlice Home Page
Greg McKenzie's Woodlouse and Lupin Page