- The Care of Woodlice
(Crustacea, Isopoda, Oniscidae)
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
and Arachnids (Spiders and Scorpions etc) and Myriapods (Millipedes
and Centipedes) a hard exoskeleton and jointed limbs; they are
in fact members of the Class 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 oter 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.
A Couple of Experiments
Humidity Responses.
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.
Do Woodlice have a Permanent Home ?
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 extention 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.
Taxonomy :- Order Arthropoda,
Class Crustacea,
Order Isopoda,
Suborder Oniscidea.
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- by Stan Sparks
gordon@earthlife.net
© Earth-Life Web Productions
Bringing Insects to the World http://www.earthlife.net/insects/
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