by Matt Gibson
Spider mites are actually arachnids, though they’re tiny—nearly microscopic. These common garden pests belong to the family Tetranychidae, and they are one of the most common insects gardeners must be vigilant against that can plague houseplants as well as invade plants cultivated outdoors.
Though many species of spider mites are virtually invisible and most adult specimens are no larger than the period on the end of a sentence, these little guys spin silk and form webs just like any other spider. And despite their small size, spider mites can be a big problem for gardeners. Let’s take a look at what you need to know to detect, prevent, and defeat them.
There are many different species of spider mites, which come in a variety of colors and sizes. The spider mite grows in a five-stage life cycle, starting as an egg and evolving through a larval phase and two nymph forms until it finally reaches its last stage as an adult. Some female spider mites live 30 days, producing as many as 100 eggs each during their lifespan.
As an example of their potential to wreak havoc in the garden, consider that the two-spotted spider mite goes from egg to adult in as little as five days. The spider mite’s natural tendency to grow the ranks quickly means that spotting them and eliminating them quickly, before a population explosion can occur, is vital, especially for gardeners working in hot and dry climate, where they thrive. A large infestation of two-spotted spider mites will be noticeable because it will have your plants’ leaves and stems coated in a thick layer of webbing. Once spider mites have gotten this kind of hold on your plants, they can be tough to get rid of, but take heart—it’s not impossible.
Spider Mite Damage
Another quality that makes spider mites particularly harmful if they get to your plants is their diet. These insects feed directly on the chlorophyll that the plants use to convert energy during photosynthesis. The mites use their sharp mouths to pierce the cell walls of plants, enabling them to easily suck out all the vital fluids within the cells.
If spider mites are left to their own devices on an affected plant, its damaged leaves will turn brown and eventually fall from the plant. If spider mites are allowed to infest for too long, the entire plant will die—and the spider mites will likely move on to the next plant in your garden in search of more food.
Identifying Spider Mites
If you see stippling or webbing on any of your beloved plants, get out a magnifying glass and check both sides of the leaves for tiny spiders. If you are still unsure whether spider mites are to blame, take out a white sheet of paper and gently tap a leaf above it to knock off any mites that may be attached. If you do have a spider mite infestation, you should see quite a few of them, looking like tiny black dots and moving across the surface of the paper.
There are three other signs of spider mites that you will want to have in mind when doing maintenance and checkups on your plants. First, look for small yellow, tan, or white spots on the leaves of your plants. These are the marks that the mites leave on the leaves when they feed on the plant’s chlorophyll. The second sign is the appearance of very small black, white, or red spots on the plant, spots that move. These are the tiny mites themselves. The third sign to look for when checking your garden for spider mites is the cotton-like white or off-white webbing the mites will leave on the underside of your plant’s leaves.
Make sure to check outdoor gardens for symptoms of spider mites every two weeks. Because indoor environments tend to be drier, and conditions indoors also usually remain more stable than outdoors, indoor plants should be checked for spider mites each week instead of biweekly. Spider mites are particularly fond of fruit trees, vegetable plants, and many popular ornamental plants, such as roses, so pay close attention to these crops when you’re searching for these microscopic arachnids. If you believe that one or more of your plants have spider mite symptoms, isolate them immediately, then get started on sending the mites to their next life.
How To Prevent, Control, and Kill Spider Mites
Though getting rid of spider mites once you notice an infestation can be a tall task to tackle, it is not impossible. With the right knowledge and a bit of persistence, the spider mites don’t stand a chance. And as savvy gardeners know, an ounce of prevention is worth a pound of cure when it comes to avoiding diseased plants.
Method One: Prevention
The best way to get rid of spider mites is to never have them in the first place. As directed in the paragraphs above, check your indoor plants and your plants in outdoor gardens regularly for signs of spider mites. Spider mites like hot and dry conditions, so be sure to provide your plants with consistent moisture, especially during warmer weather or droughts.
Before purchasing new plants, be sure to check them well for signs of spider mite damage. This step may seem like a no-brainer, but buying infested plants is more common than one might think. The last thing you want to do is bring a large group of spider mites home for a free-for-all in your garden, so be sure that any new botanical additions to the landscape or indoor decor are free of disease and unwanted pests before bringing them onto the property.
Method Two: Water Pressure
When you’re watering, clean your plants using a high-pressure water hose spray nozzle. Just be sure to adjust the nozzle on the hose to a setting gentle enough not to harm your plants, but still forceful enough to create a blast that can send insects flying. Be sure to spray all of the plants down thoroughly, especially paying attention to the underside of the foliage, where spider mites love to hang out. You will have to repeat the attack two to three times to completely get rid of the spider mites, so be persistent and keep at it.
Method Three: Ladybug Army
Another way to handle a spider mite infestation is to introduce some of their natural enemies into the environment and let them go to war with the spider mites on your behalf. Ladybugs are the natural enemy of the spider mite. That’s right, adorable little ladybugs! This method is actually insanely cool. You are literally enlisting an army of cute little ladybugs (or other parasitic mites) to go to war with the spider mites. You get to play the role of the general, and you get to release your army and watch and cheer as they feast on the spider mite invaders. How cool is that?
Aside from ladybugs, other natural predators of spider mites include: miniature pirate bugs, lacewings, big-eyed bugs, predatory thrips, predatory mites, and last but most certainly not least, spider mite destroyers (yes, that is the real name of an insect that you can purchase to kill your garden’s spider mites).
Method Four: Horticultural Oils and Insecticidal Soaps
Horticultural oils, such as neem, canola, or cottonseed oils, can be used to treat spider mite infestations as well. You can buy these oils in a ready-to-use spray or as concentrates. Dilute the concentrates with water as a one to two percent solution, or mix two and a half to five tablespoons of oil into every one gallon of water. Put the combined solution into a spray bottle and use it to spray down the foliage of your plants entirely. Treat your outdoor plants late in the evening to avoid accidentally harming bees or other beneficial insects. Cover the leaves top to bottom, making sure to target the underside of the leaves where the spider mites love to congregate. Never spray your outdoor plants (with anything) if it is 90 degrees Fahrenheit or hotter.
Insecticidal soaps penetrate the spider mites’ exterior and dry them out, killing the insects by dehydrating them completely. Some plants are sensitive to insecticidal soap, so be sure to test this strategy out on a few leaves as a test for a few days to see how it will react before treating the entire affected area. Treat twice, two days apart, in the late evening after the sun has gone down. Never treat outdoor plants with insecticidal soap when it is 90 degrees Fahrenheit or hotter.
Whatever you choose to treat the infestation with, do not use a pesticide, as spider mites are resistant to pesticides. All you will be doing by fighting a spider mite with a pesticide is effectively killing off all the beneficial bugs that might have eaten the spider mites for you.
Method Five: Sulfur Spray and Miticide
In cases when a spider mite infestation is especially bad, or if it has been left untreated for a long time, sulfur spray is an option for gardeners to try that can set things right. If you have already tried using soap or oils to treat your garden or houseplants, you’ll need to wait at least 30 days from those treatments before it’s safe to use sulfur spray.
You can also use a miticide to kill the spider mites off completely, but do note that both miticides and sulfur sprays can kill off some of your garden’s beneficial insects in the process.
If you have an especially bad infestation of spider mites or if one method at a time isn’t doing the trick, you might consider using a multi-pronged approach. If worst comes to worst, try combining some of the methods illustrated above to give you an extra edge in your battle against the spider mite invasion.
Videos About Fighting Spider Mites
Looking for a safe and easy fix to get rid of spider mites? This YouTube user has you covered:
Having issues with both spider mites and whiteflies? This video teaches you how to eliminate and control them both:
Want to Learn More About Fighting Spider Mites?
Not sure whether spider mites are the issue? Here’s our very own guide to identifying common houseplant pests.