The Lower Mainland of BC tends to enjoy very damp spring and early summer weather. This dampness creates the ideal habitat for Woodlice – often called sow bugs or pill bugs. These are the small, grey, segmented animals that can be found beneath rotting wood, garbage cans, plant pots, and so on. They gather, sometimes in large numbers, anywhere where moisture collects and lasts throughout the day.
Woodlice are actually crustaceans of the suborder Oniscidea, and are more closely related to shrimp than to insects. There are more than 3,000 species of woodlice in the world, and dozens of different species may be found in the home garden. Members of the genus Armidillidium are notable because they can curl their bodies into a nearly perfect ball as a defensive measure. Other woodlice (sow bugs) just push through the soil like little pigs, hence their family name Porcellionidae (porcelli = little pig).
Woodlice are largely nocturnal and live on decaying vegetable matter, occasionally grazing on tender seedlings, ripe strawberries, and other cultivated plants. They may follow slugs and snails and feed on plants that were previously undamaged. In greenhouses, or where ample moisture or humidity exists, they may become abundant enough to cause damage to more mature plants.
It should also be noted that woodlice play a key function in breaking down organic matter from one stage to another. They are the first creatures on the scene when newly fallen leaves need to be broken down. They can quickly skeletonize leaves, leaving behind matter in a form that is then processed by a host of other, small soil-dwelling animals and microbes. In this regard, they are beneficial species for the creation of healthy organic soil. They also form part of your garden’s food web, feeding spiders and other garden predators.
Prevention is the key to controlling Woodlice. Because they are crustaceans, they require moisture in order to breathe through modified gills. Growers with very damp gardens should expect to find them, and there is little point in trying to get rid of them. In some respects, the presence of Woodlice shows that the biological processes of the garden are healthy.
By keeping seedling trays elevated on tables, and generally reducing Woodlice habitat around patio areas, damage to plants can be minimized. If they are a problem in garden beds, it may be an indication of over-watering. If they are present in raised beds, the wood of the structure may be decaying. As with slugs, removing their habitat is the most effect control method. By transplanting seedlings into your garden, you can nurture young plants passed the stage when they are attractive to woodlice.
Diatomaceous Earth will, of course, kill woodlice. But it will kill all the other creatures with exoskeletons that come in contact with it. It is an indiscriminate pesticide, so should be used only with purposeful thought and great restraint. Consider that the spring population boom will soon be over, and as the soil warms in the summer, your garden will be less attractive to woodlice.