Spider mites on Marijuana Plants

Everything you need to know about those nasty little bugs

white bite marks all over leaf

Hey guys and welcome (back) to Free the Tree! This time around we’re going to cover those nasty little bugs… Spider Mites. They are related to spiders, ticks and other mites.
This little guys are one of the most common cannabis pests, giving a hard time to indoor and outdoor growers all over the world since they can be very difficult to get rid of.

We’re going to cover specifically how to deal with spider mites during on marijuana plants and in your grow room. We will also cover the different ways to deal with them during the different stages of the lifecycle of Marijuana.

This is actually something that’s going on with our current culture… started seeing sign on a first leaf about 3 weeks into the flowering stage. At first we were thinking that it was something else, some type of deficiency so we didn’t cut the one leaf that was infested at that time.. what a mistake we gave them time to spread.

Table of Content

I. Knowing more about Spider Mites

II. Dealing with Spider Mites in a Marijuana Indoor Culture

III. Testimonials and stories

  • Seen around the web (coming soon)
  • Our own experience (coming soon)
  • Share your experience! (coming soon)

IV. FAQ around Spider Mites and Marijuana

  • Do Spider Mites bites humans?
  • Can I get Spider Mites from clones? (coming soon)
  • Can I get Spider Mites from marijuana cuttings? (coming soon)
  • Do Spider Mites come from outside? (coming soon)
  • Can I get Spider Mites from people? (coming soon)

V. Spider Mites Myth Busting

  • Truth or Myth – Spider Mites can reappear months later!?!
  • True or False – In less than a month you can have a colony of over 1 Million  individuals (coming soon)
  • Spider Mites explode in very humid conditions (coming soon)

I. Knowing more about the Tetranychidae Family (aka Spider Mites)

Characteristics of spider mites

As we said we personally had to deal with this issue, and spent sooooo much time searching on the internet for information. From Grow Journals to blogs, passing by sites selling products and our local grow shop, we searched everywhere for info, heard everything and it’s opposite.

After that struggle, we decided to regroup everything in one spot, here’s a list of the different characteristics, hope it helps out!

Spider mites Characteristics
Family Spider mites are part of the Tetranychidae family of Acari’s which includes over 1 200 different species.

The most common types are the

Environment Thrives in hot and dry environments
Size of adult An adult spider mite is under 1mm long, making it almost invisible to an untrained human eye.
Lifespand Spider mites can live up to 2/3 weeks.
Hatching and
sexual maturity
Under optimal conditions (27°C/80°F):

  • The eggs will hatch in about 3 days.
  • The newly born will become sexually mature in as little as 5 days.

On average 75% of newborns will be female.

reproducing cycle Spider mites become sexually mature in 3 to 5 days, after which they can lay up to 20 eggs a day.
If the full life of a spider mite it will lay hundreds of eggs.
Visible Colour Depending on the type of mites they will be either:

  • White
  • Red
  • Black
  • White with 2 black spots (aka the 2 spotted mite, fierce for marijuana cultures)
Fertility of females Once a male has fertilised a female she is fertile for life. Meaning that every day she can lay 20 more eggs without needing a male around.
This is another reason why these little guys are so vicious
Birth of Males and Females When mated, females avoid the fecundation of some eggs in order to produce males.
Only fertilized eggs will produce females.
Un-mated and unfertilized females still lay eggs that originate exclusively haploid males. 
Generally Spider mites will keep a nice balance of 75% Females and 25% in order to fully infest a plantation very quickly.
What do they feed on Spider mites feed on the leaves by removing the chlorophyll (green pigment) with their stylet like mouth.
This is why you see these white marks on the leaves, those area’s are deprived of chlorophyll, thus their green color.

Keep in mind that a leaf without chlorophyll cannot participate in photosynthesis.

Level of danger
for plants
HIGH – This suckers will invade your place, at first slowly, but the more mites you have the quicker they invade.
This is especially dangerous since the invasion in generally discovered when it’s too late.
Don’t wait until they’ve conquered multiple plants, as soon as you spot that base leaf(s) get rid of it/them! (below for more on that)
Plant invasion capacity Spider mites invade by colonising and feeding on leafs. Being so small a single mite doesn’t cover much ground, a colony on the other hand…
Once the leaf is covered, some of the female mites of that colony will migrate to a new leaf in order to feed on it.This happens much faster that you might expect, within the first rounds new-borns some of those little guys will go search for their own leaf.Generally they will stick to the same plant except if:

  • Leafs are close and/or touch which is generally the case in a grow room. This makes it easy for a mite to pass on to a new plant.
  • You main leafs already have a couple mites on them, the one’s searching for new ground prefer to start off on an un-colonised leaf.
  • Your plant it totally colonised. At this point they have no other choice but to invade another plant.
    Generally they will have already spread to other plant via leaf proximity before this happens
Speed of spreading For this let’s take back the numbers we gave you further up.
1 female mite can lay up to 20 eggs a day. In 8 days the 20 eggs have hatched, 75% of those are females and are ready to lay eggs. So:

  • 8 days after having 1 mite you will have 16 females mites, each day laying 20 more eggs.
  • 3 days later try to guess how many you’ll have…. yep that’s it!
    61 total females, and over 3100 eggs
  • If untreated, by day 21 you’ll have more than 6500 females and almost 400 000 eggs.
  • And by day 30.. that number of mature females would be up to over 840 000 with over 40 million eggs and non-mature spider mites.

If you remember right, the lifespand is of 2/3weeks. At the latest, when your first spider mite naturally dies, she will have given birth to a colony of over 6000 individuals, scary!

As you can see the spreading is exponential, this is why you must identify and treat them quickly and swiftly, it’s no joke. The survival of your babies is at stake.

How do they spread Coming soon
Genera Spider mites include over 1 200 species. The most common for marijuana growers are the
If you want to know more on the different species of this type of mite, check out the Wikipedia page dedicated to them.
Resistance to treatment High – Spider mites are known to develop resistance very quickly. For example some individuals that aren’t killed or the eggs can become immune to whatever you used.

It is important to have 2 different counter-measures, whether they’re organic or pesticides so that in case one individual has become immune you kill it in the second round. 

Predatory mites The best predator are actually lady bud larvae’s; they will feed on the spider mites and their eggs and will not harm your plant. Introducing these insects within your ecosystem is a great counter-measure for spidermite infestations, especially for outdoor growers.

The lifecycle of Spider Mites

In optimal conditions, from egg to death the lifespan of Spider Mites is a little over 3 weeks, in the best cases. In that period in time just one of those small little spiders can devastate a harvest.

Here’s the different stages of life and their average length.

Stage of life LENGTH IN TIME
Hatching period As short as 3 days in a hot (27°C/80°F) and dry environment
Sexual Maturity Spider Mites will reach sexual maturity in as little as 5 days. It can take longer if the environment is cold or humid.
Mating period Female Tetranychidae are active from 2 to 4 weeks, laying up to 20 eggs a day. This gives them time to reach hundreds of eggs  within their life.

This is also the stage of their life where they create the webbing on your plant in order to safely lay their eggs.

If you start seeing the webbing with a naked eye and without using water to spray under the leafs you’ve got a serious infestation on your hands

Post-mating period As most animals (basically all except humans), once the female is no longer able to lay eggs she will die.

Spider mites spreading – Step by Step

Spider mites come in waves and it gets worst and worst with time. To an untrained or un-attentive eye the first signs can passed unnoticed, when it is noticed generally it’s too late..
Here’s what happens step by step, if you’re currently seeing the first signs of an infestation don’t wait, act now!

Step 1 – White bite marks on the first base leaf

The first signs on a spider mite infestation will be the presence of white bite marks on one leaf. This leaf will is called the base leaf. If it’s the very start of your infestation this is where all the spiders and eggs are. Here’s a couple pictures

First white mark of Spider Mites on our flowering weeds

Step 2 – Spider Mites spreading on other leaves of marijuana plant

Once these little guys have set up their first colony they’re going to go conquer the other leafs of your cannabis plant. They will go invade to the closest leaves first, meaning the one’s above, under and at that same level as the base leaf. Here’s the invasion on one of our plants.

As you can see on the pictures below, once they started setting up in one leaf they go to a new one, set up on that one and keep doing so. Very quickly you will realise that they’re all over the place and many of your leaves are going to have to go..

white bite marks all over leaf
spidermites spreading to other leaves and plants

Step 3 – Spider Mites invading your other plants

Since plants in indoor cultures are generally close to each other, spider mites can go from plant to plant fairly easily, great for them, horrible for us.

In order to avoid this:

  • Cut the infected leaves, or at least the main base leaves
  • Make sure your leafs aren’t too close or touching
  • Keep wind blowing around the top of the leaves and over the medium of the plants
  • Keep humidity high
  • Drench your leaves every night about 15 minutes before lights off

Putting in place these different steps will bother them and reduce their spreading speeds. That doesn’t mean that they won’t spread, they will just do so much much slower.
Here’s the spread in our grow room, the first and last pictures show the invasion of new plants while the middle one shows a global view of the impact on our grow house.
Now keep in mind that this is considered as a small infestation, caught rather quickly

Step 4 – Webbing between plants and on your buds

Once all your plants are nicely infested and colonies have set up on each plant they will start webbing over your marijuana buds and between the plants.

If you can already see webbing than you have a big spider mites infestation for sure, and on top of that if you’re in the mid/late flowering stage your harvest is pretty much doomed, you’re going to want to focus on cleaning your grow room out to be able to grow again peacefully.
If you’re still in the vegetative stage and the early flowering, by acting quickly and seriously your plants may recover, especially during the growth stage. You might loose a couple weeks in order to grow some new leaf mass but your harvest isn’t doomed.

Again with spider mites these are the 3 key points:

  1. Prevention, prevention and preventiooon!
  2. Spotting the signs and dealing with the infestation quickly and swiftly.
  3. The golden rules, never let your guard down

Here are some pictures of fully invaded indoor cultures, and a reddit thread about an indoor grower dealing with an infestation this bad during the flowering stage.

Webbing around leaves due to spider mite infestation
Whole grow room invaded by spider mites

The Environment and Spider Colonies

Spider Mites are extremely sensitive to the temperatures and humidity levels within their environment, making this once of the strong tools in order to reduce spreading. It’s definitely a band-aid but it can save your harvest.

What environment do Spider Mites hate?

In short in order to limit the spread of spider mites:

  1. Keep temperatures low
  2. Keep humidity high
  3. Have a good ventilation system
  4. Point fans on your marijuana plant

This might be useful especially if you’re too far into your flowering stage since it might be too late for all other solutions, even Neem Oil (Here’s The Wikipedia for more, but we’ll also cover it below) will leave a taste in your buds once dried.
It’s very effective during the vegetative and early flowering stage but if you’ve only got a couple weeks left it’s really not a good idea. This leaves the environment within your grow room might just be the only thing left for you to do.

Here’s more detail on what Spider mites hate:

  • Keep the temperatures below 24°C (75°F) at all times.
    At night try and get it around 19°C (65°F). You’re staying within the ranges that are alright for your marijuana plant, but a little cold for those suckers. If your plant handles it, get the temperatures even lower at night.
  • Keep the humidity high, at the very least around 50%, if you can and don’t see any bad impacts on the plant, get around 65%.
  • Ventilate well the room and fan your plants. Spider mites like it still with no wind, so get some wind action going!
    You want at least the leafs to be moving around. Since they eat up and lay their eggs under the leafs, this will annoy them and reduce the amount of eggs they lay as well as the amount of leaf mass they eat away.
  • Have good air filtration systems. For the same reason as the previous, spider mites like still environment to develop their colonies. With a good air filtration system the air in your grow room will circulate better disturbing those little buggers that are eating your plant away.

This is the type of environment you want to reproduce in your grow room in order to limit the expansion of the spider mite colony within the grow room.

Thriving environment for Spider Mites?

Spider mites thrive in hot, humid and still environments.
If you have low humidity levels (below 35%), hot temperatures (above 28°C/82°F) and a bad air filtration system you’ve created a perfect area for spider mite proliferation.

Spider Mites in the USA

If you’re in the USA you must be especially careful for spider mites. The Federal Government uses spider mites to kill weeds on the highways..
Yeah you heard me right, driving down the road and then checking your grow room can get you infested, so make sure to put in place all the prevention steps as possible!

The two spotted spider mite

Coming soon

How did you get spider mites?

Figuring out how you got your spider mites is also a very important step into solving the issue since it will enable you to avoid getting them again.

The first step is to establish a timeline, when did you see the first signs of spider mites?
Alright did you do anything special in the days before that? Whether it’s visiting a friends grow room, receiving new cutting, buying pots at your local grow shop?

Anything that you’ve done out of the ordinary and has come in your home. By doing this my personal suspect is the new pots I bought at a local shop, that’s the only thing that changed.

Now keep in mind that they could also be coming from outside, as long as it’s not winter time. In that case you should be setting use constant counter measures to make sure a new colony doesn’t make your grow room their home

II. Spider mites and Indoor Marijuana

In this part we’ve grouped together all the info and tips we’ve gathered in order to limit, control, kill and prevent the invasion of spider mites within an indoor marijuana culture.
If you’re looking for info on outdoor culture here’s a good thread on icmag covering the subject.

How to identify spider mites

In short here are 4 easy ways to identify spider mites on your marijuana plant:

  1. White bite marks on your leafs
  2. Spider Mites Eggs
  3. Webbing on the Leafs
  4. Looking with a Pocket Microscope

Let’s go more into detail of each way to identify the presence of spider mites

White bite marks on your leafs

The first signs of Spider mites are small white marks on the leafs like to one’s on the pictures on the right. Many growers think it’s some type of deficiency (as we did) and don’t treat it, which is the worst thing to do since you’re giving them time to spread.

The first picture is our very first infested leaf, if we would of cut it right away the issue would of been much smaller for sure.

So If it’s the case for you, the best thing to do is cut them ASAP, put them in a trash bag, poor some alcohol in there and throw it away in a trash can out of you home.

If you don’t do so, After a while you will see this spreading more and more on those leafs, then for leaf to leaf and finally from plant to plant.

Spider Mite Eggs and Webbing under the infected Marijuana leaves

Once the colony has developed you might start seeing some black spots and webbing under your leafs. It’s so small without some couple tips it’s very hard to see, here’s some tips we’ve found to be useful at that step.

How to spot Spider Mite Webbing underneath the leaf

I don’t know if you’ve noticed but after the pink morning, when everything is nice and humid it’s very easy to spot spider webs, little drops of water are caught up in it revealing the webs.

The idea here is to recreate this. About 15 minutes before your lights shut down, spray the top and bottom side of your leafs with pH’ed water. Once this is done inspect carefully the leafs you suspect are infected. If you see small little shiny lines, then your gut feeling is most likely right and you’ve got some spiders

How to spot Spider Mite Eggs underneath the leaf

This one is a little tricky since they’re so small, here’s how to do so:

  1. Take a white sheet of paper and place it under the leaf
  2. Tap vigorously the leaf and stem of plant over the paper
  3. Remove the sheet of paper
  4. Do you see black ball or pollen like dust on the paper? If so, those are most likely eggs that were getting ready to hatch!

On the first image you can see how the mites set up under the leaf, and on that second one… what will happen if you don’t deal with the situation!

Close up on back of the leaf showing eggs, spiders and webbing

image credit to University of Georgia

image credit to bigbudsmag

Spider mites under a pocket microscope

Unfortunately I wasn’t able to get a picture of what I could see, but let’s just say that after doing this all hesitation will be gone.

With the most basic pocket microscope and a still hand you’ll be able to see the spider mites and their eggs, the only hard part is to close down to them.
In order to do so, cut off one of the most impacted leaves, turn it around and try to identify little spots on it.

Once you see them, place your pocket microscope on that area and start searching, slide slowly and search for little transparent balls or these little spiders. The balls are their eggs, the moving things.. well the spider mites.

Once you’ve seen them there’s no more doubt! You’ve got a spider mite infestation, and hopefully you’ve already been implementing steps in order to prevent further spreading.

Small microscope used to analyse trichomes

If either of these test and positive get active on implementing the solutions! The worst thing to do is wait and see, because once you will be positive it will be too late, as they say; Better safe than sorry

What is the base leaf

What people call the base leaf is basically the leaf the most effected by the spider mites. This is where the mites start invading your plant, spreading from leaf to leaf. Removing this leaf will strongly reduce the speed of spreading, although in itself it is not enough to get rid of all individuals and eggs.

How to identify the spider’s base leaf

Look for the leaf that is the most impacted, or the first one that showed signs of white bite marks. This is the best way to identify the point of start of the infestation on your plants.

Once the bugs spread they will make new base leafs on each new plant, don’t hesitate to remove them in order to slow down the expansion of the colonies

How to limit spider mite spreading

There are multiple ways to reduce the speed at which the spider mites spread.

  1. Put in place an environment that they dislike. We covered this further up in this article
  2. Every night about 15 minutes after lights out spray warm water on your plants.
    You’re going to want to drench the top and bottom of your plants, don’t go easy on this!
  3. Put a fan over the Apex of your plants and over the mediums. They won’t lay as many eggs if the leafs are moving.
  4. Keep your plants from touching.
    If your plants that are close or touching spider mites will be able to go from leaf to leaf, making it much easier for them to spread into your whole plantation. At the first signs of spider mites get some space between your plants (which should already be the case)
  5. Keep your grow room clean.
  6. Keep any organic mater out of your grow room.
    Whether it’s sticks, soil or leafs, keep your grow room as tidy as possible, removing yet another place these suckers can go hide and wait for the good moment to come back.
  7. Don’t stop the efforts once the signs have stopped!
    They’re known for their disappearing act, and when they come back its with a vengeance! So keep spraying, at first every days, then every 3 to 5 days (hatching length of the eggs).
  8. At the end of each cycle clean your grow room out with peroxide.

How to kill spider mites

Still gathering our pics, coming soon

Killing them during the vegetative stage

Killing them during the flowering stage

Wiki How put together a nice article on getting rid of spider mites indoors and outdoors, if you’re missing some info you might find it over there, or let us know! we’d love to add more if something is missing

Spider mite prevention

Still gathering our pics, coming soon

Stories and documentation on spider mites

Still gathering everything together, coming soon

Spider Mite FAQ

In this part of the page we decided to group together all the frequently asked questions on spider mites. We noticed that many sites answer bits and pieces of the picture but to find one place with everything not so easy.
If we didn’t answer you’re question don’t hesitate to send us a message (contact in the header) and we’ll get to it ASAP! 

Do Spider Mites bite humans?

Generally no. In rare occasions it’s been reported that they have which will create a small red ring around the bite.
You really don’t have to worry about this too much, since spider mites feed on chlorophyll, which is only found in plants, even if they do bite they won’t do so in a repeated way.

Spider Mite Myth Busters

After reading so many different blogs, journals, reports and research we’ve seen many different questions where everyone had a different opinion.
Most of these actually have had research done on them!
We decided to group these questions and myths together and give an answer as clear as possible.

Spider mites can re-appear months later

TRUE – Spider mite eggs have the ability to go dormant, just like they would in nature during the winter time.
These little guys will stay in hibernation mode until they feel that the weather is favorable to hatch. This is why prevention is so important.

You’ll need to combine actions of cleaning the room, spraying the plants and medium as well as keep an  unfavorable weather environment in order to make sure you kill as many as possible and that the survivors don’t hatch. And if they do, those prevention steps will kill (hopefully) them swiftly.

Share your story of Spider Mite infestation with us!

If you accept we’ll also add it into the story section so that it can help other indoor growers 😉

Another Indoor Growing issue? Here's everything we've covered so far