The saying goes: ‘if it swims like a duck, and quacks like a duck, it must be a duck’ doesn’t apply in principle to woodlice. Despite looking like insects, they are crustaceans, relatives of shrimp, that have adapted to life on land. The woodlouse (singular) is harmless to humans – they don’t sting or bite, so if you find them indoors, you shouldn’t be concerned for your health. They have gained all manner of nicknames around the world - roly-poly (I remember this one), bibble-bug, monkey-pea, chuggy-pig, and pill-bugs – and even Portugal has given it a nickname – ‘bicho-de-conta’, which translates to ‘bead bug’ or ‘counting bug’, as they resemble small beads when curled up. This behaviour is called ‘volvation’, and protects them from predators, while also protecting their soft underbelly and delicate gills from drying out.

Most species have invaded from the water

They are from the family Oniscidea, which originated from watery environments and has moved into earthy ones. Most can still tolerate being in water, and some will escape into water when disturbed. Others have colonised dry environments, even deserts, by decreasing their permeability to water loss and changing feeding activity to different times of the day to escape the heat.

Most are small to medium-sized (1.2–30 mm), with a strange number of 14 legs – different again from shrimp or crabs (10 legs) - with seven distinct segments that each carry one pair of jointed legs. And like insects, they have two antennae or ‘feelers’ - sensory organs used to navigate, smell, taste, and detect vibrations in their dark, damp environments. These are essential for locating food, finding mates, and detecting threats, with some species even using specialised ones to channel water to their gills.

Runners, creepers and clinger-ons

There are several types - runners, with large eyes, long legs, who sometimes change their colours to suit their environment - rollers, capable of rolling into a tight ball when disturbed - clingers, less mobile than the previous ones with flattish bodies which they press down on flush surfaces - and creepers, which have developed to live in narrow gaps, caves, etc. They are covered in setae (fine hair that helps them sense movement), scales, and glands. The ones we mostly see are small and oval-shaped, usually around 15mm in a brown/grey colour.

They share their habitat with spiders, beetles and centipedes, who will all eat them, along with foxes and owls, who might fancy a small snack. Mature woodlice can even turn cannibal in the mating season! Eggs are produced in the spring, and these are retained within the female’s body until they hatch. The babies, known as mancas, are kept in a brood pouch beneath the female for a few days before dispersing, shedding their outer shells several times as they grow. The average lifespan of a woodlouse is 2 years, with some living up to 4.

Infestations

A woodlice infestation can be difficult to handle and may indicate a damp problem indoors. A cluster around your guttering could mean a leaky gutter, and they will be attracted to any damp wood, mould or rotting things inside your home. Woodlice perform an important duty outside by eating decaying matter such as dead plants, fallen or decaying fruit and even animal droppings, and large numbers often occur in compost heaps, where they help break down plant material.

Unlikely competitors for racing

Historically in the UK, children raced woodlice on the back of pews at boring Sunday sermons by coaxing their runners – identified by paint specks – to greater speed by tickling them with feathers. Too much urging, and a competitor curled up into a ball and was disqualified. They have even been kept as pets in old fish tanks or plastic storage containers with a layer of damp compost or leaf litter, where they will live on kitchen peelings and can be ignored for days without harm. An excellent pet if you have an allergy to the usual fluffy ones - they don’t bark, don’t scratch the furniture and don’t leave poo on the carpet - what more could you ask for?