On the long list of possible pests on your plant, spider mites are definitely in the top 5 of most annoying and difficult to spot. Spider mites, also known as ‘spint’ in Dutch speaking countries are miniscule animals belonging to the class of Arachnids, the one ticks, mites and spiders are members of. Despite their name, spider mites are not true spiders but belong to the mite family and share similar characteristics as they can spin webs to protect their eggs and provide shelter. A little Jack of all trades, small and incognito like a mite, with the mobility and webbing arts of spiders, but exclusively vegetarian.

So this makes them very proficient at being parasites of houseplants, and the reason we often find them in our homes. A plant can handle some spider mites, but the population can quickly expand and your green buddy will eventually succumb to the infestation. The mites tend to pierce plant cells to suck the chlorophyll out, hence depleting the health and photosynthetic capacity, with visible sickness and eventually death as a result.

To inform you on how to prevent this disastrous fate for your houseplants, I’ll write a little blog post on how to spot spider mites, and how to control and combat them. Let’s start with some signs of infection.

Catching spider mites in the act

Spider mites are extremely tiny and almost impossible to see with the naked eye. Therefore we need to identify the damage done by them. Their small webs and egg capsules however can be visible when the population expands. We have been lucky in our greenhouse and haven’t had mite infestations in a long time, so personal photos cannot be provided. However I will add some I find online to provide some context. Let’s get to it then!

As spider mites suck the chlorophyll out of individual plant cells, the injuries left behind are often small dots, these may be yellow or pale. These dots are most likely to be visible on the underside of the leaf, along the main-and side vains. Overall discoloration of the leaf is a common occurrence when spider mites infested the plant, as more and more tiny perforations make it hard for the plant to remain properly green and healthy. Besides these bite-marks, the mites will also produce webbing to protect themselves and their offspring (eggs and nymphs). These webs may be the most important identifier when diagnosing for spider mites. Along with the marks, they will appear where the mites are located, often on the underbelly of the leaves but expanding and spreading as the population grows. If numbers reach extreme levels, the whole leaf and even plant can get covered in this webbing. If you have a good eye, you can even spot the critters walking on the surface, they will appear as small moving dots, often white or red, but this depends on the species.

So, to cut it short: Look for stippling on the leaves, and tiny webs on the underside.

Left: Stippling on Philodendron El Choco Red // Webbing on Ficus lyrata

Stippling/ Fading of color on Philodendron glorious

Unwinding the Webs: Controlling Spider Mites

As with most pests, there are a multitude of ways of dealing with them, with altering rates of success. To save your plant from being sucked dry and suffocated by spider mites and their webbing, let’s start with giving you some methods of dealing with them:

• Chemical Warfare: Personally, I think chemicals are outdated and should only be used as a final resort, they are bad for your health and require a lot of resources to produce. However if other options don’t succeed, they can be of great help. The insecticide ‘Spinosad’ may give you the results you’re looking for, but carefully follow the instructions on the bottle as to not damage your plant itself. Chemical warfare should never be combined with natural solutions, as they will also kill beneficial insects.
• Isolation: Your first job when spotting spider mites (or any other pest) is to isolate the infected plants from the healthy ones. In that way you can control the spread, and protect your uninfected plants from being attacked. By putting all mite-infested plants together, they will be easier to treat.
• Oils and soaps: If you’re not a big fan of chemical treatments, like me, natural oils and soaps can be a great option. Neem oil specifically acts as a natural insecticide, disrupting the mite's life cycle. When you buy neem oil, read the instructions carefully and follow them to the letter. It is important to dilute the substance before applying it with a plant-spray all over your plants. Focus on the underbelly of the leaves, as this is where the mites like to hide. Repeat the process every 7-10 days until the infestation is under control. The same applies to green soaps, the ones you’d use to remove green stains from your floor tiles. Both of these substances can dramatically reduce the spider mites numbers, but be sure to test them on one plant before spraying them on everything, to account for adverse effects.
• Predatory insects: Definitely the one I am most excited to explain! In nature, predatory insects keep pests in check by feeding on their populations regularly. In the case of spider mites we have a couple of options (or combinations) you can try. Predatory mites like Phytoseiulus persimilis and Neoseiulus californicus will hunt both young and adult stages of the mite infestation and can seriously decrease their numbers and help protect your plants from being overwhelmed. These predators can be used in combination with gall midges like Feltiella acarisuga to make the treatment even more effective, or when the mite-infestation is very extreme. More predators during high population numbers is never a bad idea. For more information and sale-options of these beneficial insects, we direct you to our webshop or the website of Koppert.com.
• Prevention: Healthy plants are more resilient to infestations, but potted houseplants are extremely susceptible to pests either way. The best way to try to keep them at bay is to keep your green companions as healthy as possible. By watering regularly and providing adequate sunlight, the chances of spider mite infestations getting out of control should be rare. Also a periodical cleaning of the leaves, to prevent dust-buildup can help a lot. Specifically for spider mites, providing a high-humidity environment around the plants can help dramatically. This is because the mites prefer warm, dry conditions so by not providing that type of habitat there is a chance they won’t swarm your beloved houseplants.

Battle won, what about the war?

By following these tips the infestation of spider mites should be kept under control. The battle at hand is won, but don’t forget to keep a regular eye on your plants to make sure the critters don’t come back in bigger numbers. The war against pests is always raging, especially during these years of global warming. Keep your eyes peeled, and soldiers at the ready, we wish you luck on the ongoing battlefield of pest-control.

Senne Note - Plantlovers' biologist