What harm do they do?
Woodlice are one of the commonest, or at least most easily seen, residents of the garden. They occasionally do a bit of damage in the greenhouse by having a nibble at young seedlings but established plants are not bothered by them. Their presence is more a criticism of the gardener for presenting them with good living conditions in the form of places to hide.
It seems a shame that, because something has more legs than us, the reaction of many people is 'how do I kill 'em?' The fact is that woodlice mainly eat dead organic matter. This means that they are part of nature's wonderful recycling system whereby this food is reduced, along with the work of other organisms, to compost. The compost enables more plants to grow and is an example of how even the smallest, seemingly insignificant, creatures play a much more positive role in preserving life on Earth than we do, with our polluting, resource- exhausting ways.
They crawled from the sea millions of years ago and since then haven't evolved much: still breathing through gills, they will usually be found in damp places, under stones or rotting leaves, where they can retain a 'skin' of water. Apparently these gills are in their knees, which probably means they aren't religious because, in kneeling to say prayers, they will asphyxiate themselves. Ancient relatives, a foot in length, can still be found 6,000 feet down in the Atlantic and The Sea Life Centre in Blackpool have some on show. There are many different species frequenting gardens but basically they share the same characteristics, apart from the foot long bit.
My selection of wildlife pictures includes quite a few of insects mating, leading my wife to label me an insect voyeur. Sadly I have none of woodlice in a compromising situation. The closest I came was when on holiday in Presteigne, on the border of Wales: I was walking along a lane about the width of a car. The sides were banked and full of wildflowers, while in the distance a cuckoo was calling. The sunshine and blue skies seemingly completed this idyllic picture until my senses reached even further heights when, rounding a corner, I came across two woodlice in flagrante delicto on a vigorously bending blade of grass. My excitement was even greater than theirs: I fixed my camera on the tripod, focused, adjusted for depth of field and was about to shoot when their exertions overcame them and they fell off.
Some species of woodlice were called pill bugs in days of yore. This was because, when touched, they roll up in a ball. People suffering upset stomachs would swallow one in order to clear up the problem.
Might be worth a try.