4 Signs of Spider Mites on Cacti (The Cause and Fixes!)
Cacti have a reputation of being near indestructible, so you’re probably less than thrilled to see your cacti suffering from spider mites. As common as these pests are, they can be challenging to properly identify. To help save your cacti, here are the tell-tale signs it’s infested with spider mites!
Cacti that are infested with spider mites will have 1) webbing, 2) discoloration, 3) stunted growth, and 4) spider mites. These pests can be eradicated by physically removing them, applying a miticide, isolating the infested cacti, and keeping them healthy.
Spider mites are one of the biggest challenges your plants can face—even if those plants are resilient cacti. If your cactus collection is showing any of the following signs, you mite want to act quickly!
Spider mites are aptly named due to their ability to develop silk webs, which can be seen on their infested host cactus. These webs will be soft and white and are normally located between stems and spines.
Of course, the top most obvious sign that you have spider mites is when you see webs on your cacti.
These soft, silken webs are created by spider mites to protect their eggs and move about easily, which is why they’re often found between spines, stems, and small crevices.
Two-spotted spider mites or Tetranychus urticae eggs can hatch and reproduce in less than a week.
Remember, some species such as the old man cactus (Cephalocereus senilis) and powder puff Cactus (Mammillaria bocasana) naturally produce harmless wooly hair. Such hair is different from spider mite webs and will grow directly out of the cactus.
In case you can’t find any webs on your cacti or are unsure if it’s due to spider mites, simply move on to the next signs to investigate your plants further!
Reddish or yellow discoloration on cacti is a sign of heavy spider mite damage. Without adequate care, the infested cacti will suffer and eventually die due to spider mites constantly feeding on them.
It’s important to note that these pests survive by sucking out chlorophyll. Revisiting some basic plant biology, chlorophyll is the pigment that gives plants their typical green color .
Under severe infestations, infested cacti will become less vibrant and possibly take on a yellow or bronze haze. The damage done by spider mites can sometimes even be mistaken for sunburn or stippling.
I noticed this can be seen at the base or top of the cactus near their spines.
This isn’t just unappealing– without chlorophyll, your sun-loving cactus will have a much harder time photosynthesizing when it has less chlorophyll to absorb light.
Over time, the health of your cactus will eventually decline, leading us to the next sign.
3. Stunted Growth
Poor and stunted growth in cacti is a common symptom of spider mites. Affected cacti will not develop new flowers or spines. It will no longer absorb water and fertilizer as well..
Considering most cacti are slow growers, to begin with, it can be pretty challenging trying to see if your cactus is struggling with stunted growth.
However, there are a few key things I look out for to help me identify stunted growth in my cacti.
For instance, if the cactus hasn’t produced any new spines or flowers, and isn’t taking in as much water or nutrients, its growth may be stunted. This is different from when a cactus enters dormancy.
Learn more in our article Do Indoor Cacti Go Dormant in Winter? The Surprising Truth!
When a plant is battling spider mites, much of its energies will be reserved to help it survive rather than grow.
Although this can be seen early on, this will gradually worsen over time as the infestation becomes more of a threat.
4. Spider Mites
When spider mites are seen on a cactus, it is undoubtedly infested. These 8-legged pests can be seen with a magnifying glass or on a piece of white paper where they will appear as moving dots.
Finally, the biggest sign your cactus is infested with spider mites is when you see the spider mites themselves.
With the naked eye, you might not see them at all! An easy way to get visible confirmation of spider mites is to carefully tap the cacti over a sheet of white paper.
You should see dots moving around on their own. Additionally, you can use a basic 10x handheld magnifying glass to view them up close.
This magnifying glass on Amazon is extremely convenient and comes with LED lights!
Spider mites have 8 legs: 4 in the front and 4 around the back. Two-spotted spider mites are the most common and will have two spots on their backs.
Pro Tip: Spray the spider mites with rubbing alcohol to prevent them from moving, so you can have an easier time identifying them. If sprayed on the plant, the rubbing alcohol should evaporate quickly and shouldn’t cause any harm to your cactus!
Where Do Spider Mites Come From? (Top Cause of Infestation)
The most common way spider mites are introduced is by buying infested plants from a plant store. Additionally, because these pests are less than 1 mm wide, they can be found in pots and substrates and easily spread to unprotected cacti.
Spider mites are unfortunately common pests that can be found all over the world, even if you keep your cacti indoors.
Where did these spider mites come from? The most likely possibility is that you had unknowingly brought home an infested plant from a nursery or a plant trade.
It’s also possible for spider mites to spread from infested gardening materials such as soil and pots, or even plant tools. Since they’re typically smaller than 1 mm (approx. 0.04 in), they can hide in virtually everything, making them impossible to detect until it’s too late.
Due to their small size, spider mites are easily carried by the wind and can travel long distances.
Another important thing to mention is that spider mites attack a wide variety of plants from houseplants and even herbs like rosemary. Therefore, it’s best to check your other plants to see if they’ve been attacked by spider mites as well.
4 Steps to Treat and Prevent Spider Mites on Cacti
Spider mites on cacti can be treated and prevented by 1) physically removing them, 2) applying a miticide, 3) isolating the infested cacti, and 4) keeping the cacti healthy.
Without adequate treatment, a cactus infested with spider mites can eventually lose its vigor and die. Time is of the essence!
Follow this step-by-step guide to help you effectively and permanently get rid of them and save your cactus.
1. Physically Remove the Spider Mites
Most of the spider mite population can be eliminated by cleaning the cactus with a damp tissue or by hosing it down. Replace the top inch of its soil and clean the cactus area with rubbing alcohol to kill any surviving spider mites.
As soon as you confirm your cactus has spider mites, the first thing you should do is to manually remove them. This will literally wipe out most of the spider mite population.
You can do this by hosing down the spider mites or by wiping them off your cacti with a damp tissue.
If your cactus has too many spines or small crevices, consider using a brush to sweep the bugs out and destroy any webs.
Besides cleaning the cactus itself, it’s best to remove the top layer of substrate and replace it with a sterile one. This won’t get rid of them 100%, but it’ll get you pretty close!
Additionally, try to clean up the area the cactus was kept by sweeping it and spraying it with 70% rubbing alcohol. This solution should kill off any remaining spider mites and prevent them from invading any other plants in the vicinity.
2. Apply Miticide
After cleaning the cactus, treat it with miticide 1–2 times a week until the spider mites are completely eradicated. This can be done with neem oil or commercial miticide. Spray the cactus thoroughly to kill the spider mites upon contact or drench the soil.
One of the annoying things about spider mites is that general insecticides won’t work unless they specifically state they’re miticides, as these solutions are made to kill mites specifically.
For a natural solution, I like to use this neem oil on Amazon both as a preventative measure and to treat active infestations.
Studies have found that neem oil can prevent female spider mites from laying eggs and can reduce their overall numbers by over 50%.
Whatever product you choose to use, it’s important to follow the instructions.
I suggest testing the product first for at least 24 hours and applying treatments out of the direct sun and grow lights, as the cacti could easily burn.
For a spray-based treatment, the cactus should be sprayed thoroughly from top to bottom to kill any spider mites.
You can also use neem oil as a systemic pesticide by drenching the soil, however, you don’t want to accidentally overwater your cacti!
Treat your cactus with miticide 1–2 times a week until you no longer see any spider mites.
3. Isolate the Infested Cactus
Infested cacti must be isolated during treatment to prevent the spider mites from escaping to healthy plants. Ideally, they should be kept in a cool and well-ventilated room under 80°F.
While your cactus undergoes treatment, it’s time to separate it from the rest of your plants. If there are multiple infested cacti, keep them far away from each other to prevent continuous spider mite transmission between them.
Although this might be inconvenient, this is much easier to endure than if you leave your infested cacti with other plants to spread spider mites to them!
Wherever you temporarily move your cactus, ensure the area has plenty of airflow to help the cactus and its soil stay dry, especially if you’re drenched their soil with a miticide.
Spider mites tend to be the most active in hot conditions, so their temporary home during isolation should be under 80°F or 26°C. It’s best to maintain this after successfully killing the spider mites off too.
If you want to avoid dormancy, make sure your cacti still receives plenty of bright light and proper care while it is going through quarantine.
With some dedication, your cactus should be free of spider mites after a couple of months or so!
4. Keep the Cactus Healthy
The best way to combat and prevent spider mites is to grow healthy cacti. By watering them consistently and providing proper care, the cactus is less likely to suffer from spider mite infestations.
Here’s the thing: spider mites do not have a favorite host and can be seen attacking all types of plants.
The plants that are most vulnerable to spider mites are the ones that are stressed and unhealthy.
If there’s one thing that cacti are known and loved for, they can withstand near-constant stress and drought.
But if you’re frequently struggling with spider mites, this same moisture stress your cacti endure could be one of the reasons why they keep being attacked.
Combined with the hot conditions that cacti are typically grown in, the chances of spider mite infestations are unfortunately quite high.
In cases like this, you may find it helpful to minimize the stress your cacti go through by watering them regularly.
Find out how to Water Succulents and Cacti the Right Way!
By coupling good plant care with regular neem oil treatments, your cacti will become much stronger in the long run and are less likely to suffer from spider mite attacks ever again!
Do spider mites eat cacti?
Spider mites do not eat or chew on plants. Instead, these pests survive by piercing soft plant tissue and sucking out the chlorophyll. If a cactus has been eaten or has lost parts of itself, this may be due to animal damage.
Are spider mites harmful to humans?
Since spider mites feed off of plant cells, there is no need for them to attack humans. However, if someone is allergic or sensitive to mites, they may experience skin irritation around spider-mite-infested plants. In such cases, it is best to remove the pests immediately.
Summary of How to Identify Spider Mites on Cacti
Although cacti are known to be very tough and hardy plants, they can still suffer from spider mites. The most common symptoms of spider mites are webbing, discoloration, stunted growth, and the presence of spider mites themselves.
These pests are usually unknowingly introduced to healthy cacti when the owner brings in infested plants. They can also migrate and be carried by the wind or spread through soil or infested tools.
Spider mites can be treated and prevented by physically removing them from the infested cacti, applying miticides like neem oil, and isolating the cacti from other healthy plants. To prevent the mites from returning, the cacti must be kept healthy and strong to make them less vulnerable to infestations.
- “Spider Mites” by L. D. Godfrey in Integrated Pest Management Program University of California
- “Twospotted Spider Mite, Tetranychus urticae” by Susan Mahr in University of Wisconsin-Madison