Spider mites belong to the mite (Acari) family of Tetranychidae, a family including around 1,200 species. Known to feed on hundreds of different plant-species by puncturing plant cells using their mouth-parts, which are needle-sharp, they can quickly destroy a plant before moving on to the next host.
Under 1 mm (0.04 in) in size, spider mites, which vary in colour, are extremely difficult to detect without the help of a magnifying glass. All too often, infestations are not discovered until the silky webbing used to protect colonies is detected, by which time they are usually well established.
The reason for this is simple: spider mite species are arrhenotochous, meaning the females are diploid, while the males are haploid. In essence, this means that both mated and unmated females will lay eggs. The eggs of unmated females will exclusively result in male offspring.
Mated females will prevent fertilisation of some of their eggs in order to produce males, while all fertilised eggs result in female offspring. The result of this arrangements is a staggering rate of reproduction.
Each female of the two-spotted spider mite (the species most likely to invade house plants), for instance, is capable of producing at least 20 minute spherical eggs per day. Considering that a female will live up to 4 weeks, eggs typically hatch within around 3 days and the young will be sexually mature within about 5 days, a single female can produce millions of offspring within as little as one month.
Signs of Infestation
Only regular inspections with a magnifying glass will reveal an infestation within its earlier stages. Fine webbing under leaves, or between stems and leaves and a bronzed, washed appearance of the plant indicate heavy infestations. By this time, controlling the infestation is often extremely difficult, if not downright impossible.
Preventing infestations from occurring in the first place is therefore preferable. Raising humidity and regularly misting plants helps to avoid spider mites, as they tend to prefer drier conditions.
Dealing with Infestations
Initial steps include immediately isolating the plant and removing damaged/ badly infested foliage and stems. An insecticidal soap and water solution, or a solution of fragrance/ additive-free dish washing liquid and water, can then be used to wash the plant carefully. Long ivy stems can be submerged in such a solution.
Naturally, it is essential to rinse the plant off thoroughly afterwards, and the water used should, by the way, be at room-temperature. This procedure should be repeated every two two three days for maximum effect, preferably accompanied by daily sprays - using a jet as hard as the plant can take comfortably - with water.As spider mites are not insects - and often very quickly develop resistance to pesticides anyway - sprays of any kind can only be effective if they are designed to deal with this pest and used frequently (daily) and thoroughly for prolonged periods.