What Is A Spider Mite? & What It Looks Like

What Is A Spider Mite? Detection, Treatment & Prevention

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If you have a grow room for cannabis indoors, you can really control the environment and growth factors. However, sometimes there are factors in your grow room which are not 100% in your control. One of the factors that is not in your control, or invaders we should say, is the spider mite. When it comes to growing pot, spider mites are some of the biggest and worst pests that you can have. What does a spider mite look like?

Well, spider mites are actually very hard to see. They are less than 1/50th of an inch long, and not any wider. They are usually a reddish-brown color, but can also be orange, brown, green, or yellow. However, most that you will see on marijuana plants are usually the reddish-brown variety. They are super small, pretty round in shape, and they do have 8 legs.

What Is A Spider Mite?

Opposed to what most people think, it is a misconception that spider mites are insects. They have 8 legs, and yes, this means that they are arachnids. They are very closely related to spiders. Spider mites are small insects which love to feed on plants, their juices, and the sap. In all reality, they are nothing more than pests.

You might find spider mites in indoor and outdoor marijuana grow operations. They are also known to be present in herb gardens and vegetable gardens too.

When it comes to plant growth, marijuana or otherwise, they are usually considered to be one of the worst and most damaging pests around.

What Does A Spider Mite Look Like?

red spider mite

Spider mites kind of look like a mix between a bed bug and a spider or a mix between a miniature tick and a spider. They are very small, less than 1/50th of an inch in length, and this makes them very hard to see.

When it comes to weed growing rooms, the ones you will find will generally be the orange spider mites or the reddish-brown spider mites.

And yes, as we have mentioned before, they do have 8 legs, but this is hard to tell with just your eyes, as they are so small that spotting them with bare eyes is very difficult, but no, not impossible.

Spider Mite Life Cycle

Spider mites have a fairly quick life cycle. During the winter, they usually stay dormant as spider mite eggs. Once the spring season hits and temperatures warm up a bit, these eggs will hatch into tiny six legged larvae. They will then seek shelter and molt into the first nymphal stage, and this is when they have 8 legs.

There are two more molts that happen before the adult spider mite emerges. What is really bad about spider mites is that they reproduce very quickly. If conditions are dry and hot, the time it takes for a spider mite egg to become a fully mature adult can be as little as 5 days, especially if there is a good food source present, such as your cannabis plant.

Once a female has mated, she can produce 300 or more eggs over a 2 week period. Maximum, they can lay up to 20 eggs for a full 4 weeks, which is as long as an adult spider mite lives.

Yes, the math is scary here, because just a few spider mites can rapidly multiply into thousands and thousands of spider mites in just a couple of weeks.

This of course causes big problems if you have even a small spider mite infestation, because if left uncontrolled, those few mites will turn into thousands before you know it, and you will have a massive and full blown infestation, and they will wreak havoc on your weed plants.

How To Tell If You Have Spider Mites

Ok, so as we mentioned before, spider mites are exceedingly small and can be hard to see with just your eyes. However, they are not totally impossible to see, especially if you have the orange or red varieties, as their bodies will create lots of contrast with your green weed plants.

So, if you see a bunch of little red or orange dots scuttling around on your weed plants, chances are that they are spider mites. If you are having trouble seeing them, a good old magnifying glass will work fine. However, there are also other telltale signs that you have a spider mite infestation in your weed grow room.

Besides seeing the actual spider mites, if you already have a fairly large infestation, you will also see small and thin, very fragile webs. Remember, this is technically an arachnid and they do spin webs.

They can be hard to spot if there are just a few mites, but once there are a good amount of spider mites present, you will begin to see small webs. These webs are usually on the underside of leaves and buds, especially on larger fan leaves, but may also be on top of your weed leaves.

Another way to tell if you have spider mites is by looking at your weed plants, specifically the leaves. Spider mites will eat away at your weed plants, and they like to start with the larger leaves. They will eat away miniature little holes in the leaves.

They can also leave little white spots behind. Moreover, once a spider mite infestation has progressed significantly, you will notice your leaves, and maybe even the buds, starting to turn yellow or brown, they will dry out, wilt, and eventually fall off, and ultimately this will cause the whole cannabis plant to do the same from top to bottom.

Why Do I Have Spider Mites On My Weed Plants?

The problem with spider mites is that their eggs are fairly resilient and can stay alive during the cold, and their eggs can get everywhere. Did you know that spider mites, and their eggs, are so lightweight that they can float in the air, even on a very light breeze?

So, if it is windy, and there are spider mites nearby, their eggs, the nymphs, or adults may have been blown into your home or blown onto the soil you are using. Moreover, seeing spider mite eggs is nearly impossible, and who knows, the eggs might have already been present in the soil you are using to grow your cannabis plant in, and then hatched once you started supplying some heat.

One thing to keep in mind is that spider mites like dry and hot conditions, and they love feeding on weed plants. So, you might have spider mites because they were attracted to the smell of the cannabis plant, and cannot pass up a dry and hot vacation spot.

Also, if your grow room is not well ventilated, and the air is very still, it’s another thing that will attract spider mites and cause them to stay. They like still, dry, and hot air, but they do not like breezy areas.

The fact of the matter is that spider mites are quite common, especially during the late spring and summer time. In all reality, if you grow pot for long enough, you will probably see these annoying pests at least once.

You could have spider mites because they were attracted to your grow room from nearby, or they could have been present in the soil you bought. You probably won’t ever figure out where the infestation came from.

Problems Caused By Spider Mites In Your Grow Room

Yes, the spider mite is one of the worst pests that you can have present in your cannabis grow room, and yes, they can affect outdoor weed grow ops as well. There are various problems that spider mites will cause.

Well, really it all starts out as a small problem, which then snowballs and causes other effects which compound and can eventually lead to the death of your weed plants.

Although the total destruction of cannabis plants is rare, a severe spider mite infestation can stunt the growth of your weed plant, keep it short, stop it from developing buds, and can infect buds, causing them to have a low THC count and not develop properly. If the infestation is very severe, it can totally kill a plant and destroy a room full of crops.

It all starts with the spider mites eating away at the leaves of your plants. For one, this creates little holes in the leaves, which on its own is not good because it causes structural damage.

This also causes a decreased rate of photosynthesis, the process by which plants breathe, absorb light and nutrients, and grow. Moreover, these small holes, once they start to grow in number, will cause your marijuana plant to start losing excessive amounts of moisture.

The more holes the leaves have in them, the more moisture the weed plant loses, and the more moisture the weed plant loses, the drier it gets, and the drier it gets, the less photosynthesis the weed plant can engage in.

The result here is stunted growth and structural damage. Spider mites can also infest the weed buds themselves, eating away at the flower that you would like to harvest and smoke.

They can cause stunted growth in the buds, they can cause lower yields and lower potency, and in worst case scenarios, this all comes together to totally kill your weed plant.

How To Prevent & Get Rid Of Spider Mites

spider mite on plant

There are a variety of methods at your disposal to prevent spider mite infections, although not too many, and quite honestly, doing so is hard, because once they are present, they multiply easily and quickly. However, luckily, there are also a few good ways to get rid of spider mites.

Yet, beware, these pests are resilient, and they may come back or you might never fully get rid of them. How do you prevent spider mite infestations, and how do you get rid of spider mites?

1. Controlling Environmental Factors

As we mentioned before, spider mites like dry and hot environments with little or no air movement. Therefore, to try and prevent spider mites from infesting your grow room in the first place, you want to turn the temperature down a bit.

Spider mites usually won’t stick around or even come in the door the first place if the temperature is below 20 degrees Celsius.

However, this can be an issue, because for the most part, weed plants need higher temperatures than that. It is possible to do this, but be careful to not damage your plants.

In the earlier stages of marijuana growth, the plants do need a fair amount of humidity.

To prevent spider mite infestations, keeping the humidity relatively high can be a solution, but once again, weed plants need a certain level of humidity to thrive, so finding a good balance can be a problem, especially during the flowering stage when the air in the grow room should be pretty dry.

On this same note, spider mites do not like wind or even small breezes. Therefore, turn on a fan and increase the ventilation in your grow room, which will also help decrease the temperature.

2. Pruning

One easy and quick solution to controlling spider mite infestations is to prune or cut off sections of the plant which are infested.

No, this is not the best solution, as you will end up cutting away parts of the plant, which in itself can cause damage and stunted growth, but it is still not nearly as bad as allowing a spider mite infestation to continue.

To do this, you want to cut away any part of the leaves well beyond where the webs of the spider mites are.

Yet, this alone will usually not get rid of all spider mites. To totally get rid of the spider mites, you will want to engage in a combination pruning and washing operation.

3. Hosing & Washing

If you are dealing with mites, after you have pruned the plants, or you can try this before pruning in order to prevent further damage, you can hose the plants off with cool water.

The water will wash away quite a few or even all spider mites, as they are not big fans of water and are not good swimmers either. You will drown and wash away most of them.

However, when doing this, do not use too much water pressure, as you can end up damaging the cannabis plants. Some people will make a mixture of 9 parts water and 1 part rubbing alcohol, which works exceedingly well.

The rubbing alcohol will kill spider mites on contact, and the water will wash them away. Don’t worry, the alcohol will not damage your weed plants, at least not if you mix the proper ratio as described above.

4. Using Predator Insects

Another method you can try to control and get rid of spider mite populations is to introduce predator insects into your grow room or outdoor garden. Hands down the best insect to introduce into your grow op to get rid of spider mites is the ladybug.

They love eating spider mites and they are always hungry. Other insects that can be used to kill off spider mites include lacewings, predatory mites, minute pirate bugs, six spotted thrips, western flower thrips, and bigeyed bugs.

This does often work, but beware that you will then mostly likely have a secondary bug infestation to deal with, although they will not harm your weed plants like the spider mites do.

5. Essential & Horticultural Oils

The next solution to your spider mite problem can come in the form of essential and horticultural oils. Do keep in mind that some of these oils can be very aromatic and pungent, so you will want to avoid getting them on your bugs and buds, as they will absorb the smell and flavor, which will then not be too enjoyable to smoke or eat.

Some of the best oils to use for getting rid of spider mites include Neem oil, eucalyptus oil, cinnamon oil, lemon oil, peppermint oil, and rosemary oil. These essential oils actually attach the central nervous system of the spider mites and kills them real fast.

All you have to do is mix a good amount of any of these essential oils with some water, in a spray bottle, and spray down your plants with a liberal amount.

6. Organic Insecticides

There are some organic insecticides which you can use to prevent spider mite infestations and to kill them too. There are various options you can go with here.

  • SM-90 – This is a type of organic wetting agent with a nice aroma. Mix it with water and apply to your plants liberally to kill spider mites.
  • Spinosad – This insecticide is totally natural and will not damage your weed plants. This stuff can be applied directly to the plants. Even better, you can put it into the water supply of your plants for long term protection.
  • Essentria IC3 – This insecticide contains a mix of horticultural oils which kill spider mites on contact. However, beware that this stuff lasts only for 12 hours, so it will need to be reapplied regularly.
  • NukeEm – This is a new and improved insecticide which will kill spider mites on contact, it is made out of food grade materials, and leaves barely any residue on plants.

We have reviewed our favorite sprayers and foggers over at this article.

7. Get Rid Of Problem Plants – The Greater Good

Ok, so this is not an ideal option, and no, it does not work if you only have a couple of plants and they are all infested with spider mites.

However, if you have a decent number of plants, and only a fraction of them are infested with spider mites, severely so, you might want to consider just getting rid of the affected plants altogether.

If the infestation is very severe, and the chances of totally quelling the infestation are very slim, it is better to get rid of plant or two, rather than letting your whole crop get infested.


The bottom line is that spider mites are horrible pests to have, both for indoor weed grow ops and outdoor operations too. They will multiply really fast, eat your plants, and worst case scenario, totally kill them. If you plant to start growing cannabis, familiarize yourself with what they look like, how to spot signs of an infestation, and how to deal with them effectively and efficiently.

Photo Credits:

1. CSIRO [CC BY 3.0], via Wikimedia Commons
2. Charles Lam from Hong Kong, China [CC BY-SA 2.0], via Wikimedia Commons
3. Eran Finkle @ Flickr CC