This wingless insect, also referred to as the sugar guest, is very common, but often in small numbers. The silver fish strongly resembles the firebrat Thermobia domestica Packard. It is essential to identify the right species, since both species have completely different requirements in terms of the relative humidity of the area in which they live, due to which the control measures of both these species differs greatly.
The presence of the silver fish, often in the wet unit, is an indication that the relative humidity is too high. It often concerns leakage or an architectural problem, such as a resounding wall. Too high humidity in (poorly ventilated) crawling spaces can cause serious nuisance by silver fish above the ground floor flooring.
The silver fish can get 7 – 11.5 cm in size and has clearly plate-shaped extensions at all breast segments. Characteristic are the two ringed antennas and the three fine ringed tail wires at the abdomen. The silver fish has a pearl shine, because the body is covered with fine scales.
The eggs are often dropped in the period from April to August on a suitable substrate, but also in seams and cracks. The female always lays the eggs in small numbers together, with a total of about 150. At 25°C and 75% relative humidity, the eggs hatch after about 28 days. The silver fish that emerge from the eggs can moult up to 20 times in their 2 to 3 year lifespan.
Silver fish shun the light, during daytime they hide in all kinds of dark places. Silver fish that live in nature in certain parts of Asia and South Europe in holes, caves, under rocks etc are very common in the Netherlands, but only in buildings. In almost every building there are small numbers of silver fish, however they live in great numbers in humid areas that don’t cool down during the winter, such as the kitchen, the shower cell or the bathroom, however also in other places with high humidity. Their food consists of product rich in starch, such as starch paste used to stick wallpaper against the wall, and moist, semi deteriorated wallpaper. This diet is supplemented with protein from the consumption of small dead insects. In addition certain types of glue can be consumed used to bind books. In the humid atmosphere in which silver fish exist, there will also be fungal growth, and these fungi are also eaten by said insects. Silver fish can only cause some significant damage when they exist in great numbers.
Prevention & Control
Because silver fish hardly cause any significant damage and because they usually live in small numbers, silverfish control is hardly ever necessary. When they frequently are found in great numbers, this means that the relevant area has a high humidity. The control measures must first be to create a dry atmosphere. This can be achieved by ventilating the area during dry weather and through dry firing. In a dry atmosphere, silver fish cannot sustain themselves. Use of insecticides is not necessary in general and even ill-advised if measures to reduce the relative humidity have not been taken yet. For the first residents of a new house, it is important to know that concrete is moist for a very long time, due to which, in certain areas, an atmosphere with a high relative humidity can be created. This means that proper ventilation and dry firing (for instance with a dry air furnace) is required. It is recommended to refrain from applying permanent flooring for a while. This will inhibit the evaporation of the moisture in the concrete. In addition, the silver fish will have to be offered as little shelter as possible; meaning: clean up as much as possible. Sometimes, the cabinets under the sink can be moist, especially if they are made of wood. Often the cause lies in a somewhat leaking or improperly attached sink drain. This will have to be resolved.