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Understanding Spider Mites

Understanding Spider Mites

Spider mites regularly infest all kinds of houseplants. They are particularly likely to target certain houseplants such as the following:

  • Room ivy
  • Fuchsias
  • Cypress grass
  • Rubber tree

That said, all houseplants can fall victim to these insects, including home-grown cannabis plants.

Since spider mites are often significantly smaller than one millimeter, depending on the species, they are primarily noticeable for their webs and their suction damage to the infected plants. You can recognize the common spider mite by their finely spun webs in leaf axils and on leaf margins. The fruit tree spider mite, in contrast to most other spider mite species, however, hardly forms webs.

Way of life

Spider mites love a warm, dry climate and a protected location. Although the pests only live for a few weeks, they can reproduce very quickly under optimal living conditions. They can even breed all year round in a warm greenhouse or on a sunny windowsill. Depending on the type and weather, the female spider mites can lay up to a hundred eggs in their short life. They eggs are usually placed on the undersides of the leaves. After about three days, the first offspring hatch from them; within six to fifteen days, the larvae develop into reproductive pests.

Spider mites are found both outdoors and in the greenhouse in summer. There they can cause damage to many different fruit, vegetable, and ornamental plants. Houseplants are also often affected by spider mites – especially in winter when the warm heating air offers them the best living conditions.


To give you an idea what spider mites look like close-up, they generally reach a body length between 0.25 and 0.8 millimeters. Therefore, most species are hardly recognizable without a magnifying glass. The most typical representative species is the common spider mite. It grows to just half a millimeter in size and is barely visible to the naked eye. There are other related varieties including the orchid spider mite, the cactus spider mite, and the greenhouse spider mite.

Like all arachnids, they have eight legs, and their eyes are usually observed as small red dots on the front body. The body is an elongated oval shape and is covered with numerous microscopic bristles. On the forebody, spider mites have a stinging, sucking mouthpiece with which they penetrate the underside of the leaves and suck out the leaf cells contents. The color depends not only on the particular species but also on the season and the host plant. As a result, the color of their body varies between pale green, yellow-green, orange, and red-brown.

We will discuss below how you don’t have to go straight to the chemical options to get rid of these pests. But first, let’s be sure you can properly diagnose the problem.

How to know if you have spider mites in your plants?

You can usually tell that common spider mites have infected one of your plants by these symptoms:

  • Fine, light speckles on the top of the leaves of your plants
  • Finely spun threads between the parts of the plant

The light speckles on the top of the leaf arise because the mites prick the plant and feed on the plant’s juices. Depending on the degree of the infestation, the leaves can change color completely or eventually dry out. Many plant owners mistakenly consider the speckles to be signs of deficiencies. So, if you discover suspicious leaves in your plants, the next thing you should look for is the spider-like threads. Since you don’t always see them with the naked eye, it can be helpful to dust the plant with a little water. The fine droplets of water make the spun webs visible. However, the spinning threads only appear with the common spider mite.

Root cause

Just like other types of mites, spider mites are active in warm and dry weather. Spider mites often appear through old soil. Because when the earth has no more nutrients, this is the perfect place for the spider mite to develop. Since even weak plants are often infected, it often helps to repot the plant and thereby give it energy and resistance.

Spider mites benefit from their size and mobility. As a result, spider mites can easily reproduce through contact from plant to plant. Spider mites poke small holes in the leaves, sucking the nutrients from the plant. As a result, the plant can no longer transport or absorb nutrients and will most likely die from prolonged infestation. If the spider mite is not controlled well in time, it will become a fairly stubborn plague for any plant.

Spider mites feel particularly comfortable in dry heated air

The occurrence of spider mites has a common cause: dry indoor air. For this reason, spider mites mainly occur in the autumn and winter months, when the air in the room becomes noticeably drier due to heating. The tiny plant pests feel particularly comfortable in the dry indoor climate.

Controlling spider mites without the use of chemicals

Like most pests, you can easily control the spider mite by eliminating the cause of the infestation. For spider mites, this means managing moist air. Spider mites cannot tolerate high humidity. Here’s how you do it:

  • Rinse the infested plant thoroughly with water in the shower
  • Put a transparent plastic bag over the plant and close it directly over the entire plant
  • Let the plant stand for two weeks

The effect is simple. The bag looks like a greenhouse. Inside, the air humidity rises so much that the mites die within two weeks. A variety of naturally derived mite sprays may also be bought online or you can research your own recipe to try.

Remove spider mites with pesticides

In the case of particularly heavy infestation, or if many plants are affected by spider mites, the above procedures may no longer be sufficient. In this case, you can use “gentle” pesticides on your cannabis plants. For example, there are rapeseed oil-based preparations. The oil lies over the mites and closes their respiratory openings. Another option is neem crop protection products. These preparations are based on the active ingredients from plant parts of the neem tree. The plant contains various substances that can help against pests. If you choose plant protection products to free your plants from spider mites, it is best to consult specialist retailers for suitable agents. Also, you should always read and follow the instructions for use carefully. This also applies to preparations comprised of natural active ingredients.

Variants of the pest

Spider mites come in different variations, most of which are plant-specific. For example, the common spider mite is common in greenhouses. Depending on the spider mite species, other plants are susceptible. Examples of susceptible plants are Alocasia and Polyscias. Above all, however, plants that are often in dry soil are most vulnerable to spider mite infestation.

The spider mites often sit under the leaves. Because they are very small and do not move much, meaning they are difficult to spot. The spider mites are about 0.3 and 0.5mm in size and have a pear-shaped body. Depending on the species, spider mites are brown, red or yellow-green. The best way to recognize a spider mite infestation is on the leaves of the plants. With prolonged outbreak, white tissue often appears on the underside of the leaves.


Precaution is better than trying to get rid of mites. Experts therefore recommend spraying your plants with pesticides occasionally. You can also prevent infestation by spraying with water, as spider mites prefer a dry environment. There are several ways to combat spider mites. First of all, professionals recommend removing the affected leaves and branches. Try not to touch the healthy branches with the affected branches. If the infestation is severe, it is best to use a pesticide.

In contrast to various louse species, the spider mite has little resistance to protective agents. The size of these parasites is particularly difficult to control the spider mite. These are easy to miss and can then easily spread again. Therefore, the plant should be sprayed thoroughly.

A Tip: In the evening, spray the plant with water containing 2 percent yellow soap and 1 percent alcohol. Since the eggs hatch mostly in the evening, this is particularly effective. You can also increase the humidity and reduce the temperature because spider mites love a warm, dry environment. Spider mites are not dangerous for humans. At a temperature below 12 degrees, spider mites stop developing and go into their resting stage.

General Interest

Curious about spiders and wanting to learn more? Here are some fun facts! The spider mite family (Tetranychidae) includes around 1,200 species. The animals belong to the Prostigmata order within the mite subclass. Like all mites, they are not insects but arachnids. Spider mites get their name because of the delicate webs with which some species cover the leaves and shoots of the host plants. The most common plant pests include the common spider mite (Tetranychus urticae), which is also called bean spider mite, the fruit tree spider mite (Panonychus ulmi) and the coniferous spider mite (Oligonychus ununguis).