The order of Isopods, of which we have various representatives in the Netherlands, belong to the class of crustaceans (Crustacea). In and around buildings, Porcellio scaber Latreille is the most common; in addition, wave the Oniscus asellus L. and Porcellionides pruinosus Brandt in the Netherlands. An isopod is also referred to as a basement moth or sow bug.
Isopods are fairly flat, oval animals. They have relatively large antennas and 7 pairs of legs. The segments located behind the 7 leg-bearing segments (6) always have a number of attachments. The animals are grey, sometimes yellowish or purple-brown, with lighter or darker spots and with a length up to 1.8 cm.
Isopods usually live in the field under rocks, under the bark of trees, under fallen leafs, in decayed wood etc. Because they are nocturnal animals, they can mainly be found in dark places. In moist basements and storages where vegetable material can be found, isopods can exist as well. Dehydration is fatal for these animals.
However, the species Porcellionides pruinosus Brandt exists in relatively dry places, under rocks, wood, etc. Isopods can only be harmful in great numbers in greenhouses and vegetable gardens, where they eat the plants. They prefer to eat rotting material, in doing so contributing to the humus formation. A curious aspect in the lifestyle of the isopod is the breeding care. The females carry the eggs with them in a breeding area located at the bottom of the body, until the young larvae hatch. This form of breeding care allows the animals to, after invading a certain space, such as a basement, populate it quickly if the circumstances are favourable in terms of temperature, humidity and food. After leaving the mother, the larvae go through their first moult stage. Afterwards they can moult dozens of times. The adult isopods can reach ages up to two years old.
Prevention & Control
Often, isopods invade houses, caravans, tents etc, in particular when it is very dry outside. They hope to find more favourable living conditions indoors (mainly moisture). Because the accommodations of these animals in the immediate vicinity of houses often consist of compost or manure heaps, heaps of garden waste etc, it is important to clean up these accommodations from which they can invade the houses. Garbage dumps can also form a source of isopods. To prevent the invasion of the house, one can fit the passages, such as air vents, with fine mesh. In addition, proper prevention consists of sealing cracks and seams in the exterior wall. Inside, moist places should be avoided with better ventilation, heating, etc. Optionally, one can place flower pots upside down outside, filled with moist leafs or hay, or a damp mop, under which the animals that are looking for a favourable location, can gather. The day after, one can kill the isopods using boiling water, for instance.
Chemical extermination is ill-advised, since after a while these favourable locations for these animals, will be populated by a new group. More important is to reduce the humidity in these locations and to remove the vegetable material. Spraying the area with insecticides is ill-advised. The isopods that hide during the day cannot or hardly be reached, whereas such a treatment can kill other insects and birds. This means that the natural enemies of the isopods are killed as well and that the control measure has the opposite effect.