Two-spotted spider mites: How to identify them and a little biology
To defeat an enemy you must know them.
I have seen a lot of people talking about mites and it tends to be coupled with a sense of despair, anger or fear. I think if there is one pest that is at the top of everyone’s hit list it is the dreaded spider mite. And for good reason! Spider mites have an incredibly broad range of hosts meaning that there’s a very good chance you have at least one plant that mites love to dine on. Like people, pests also have their “favorite foods” and spider mites have a long list but some of their personal favorites are Alocasias, Palms and Calatheas. Which just so happen to be very large and popular groups right now.
So, you think you’ve got spider mites. But, are you sure it’s mites? Before blindly treating for something it is crucial to diagnose or identify the problem properly. When you go to the doctor with a headache and they hand you crutches that isn’t going to help too much. It’s the same thing with plants. Start thinking of yourself as your plants doctor - you are it’s primary caregiver after all! Which pest you have is going to determine how you treat for it which we will cover later.
It’s also very handy to understand the pests life cycle because in some cases there may only be one point in their entire life cycle in which they are vulnerable. Or maybe they complete different stages of their lives in different areas. If you are constantly only treating one area it will be slow going and it would be much faster to use a three pronged attack. I say attack because when it boils down, this is war. Strategy is key.
So let’s get back to spider mites - how do you ID them? One of the easiest ways is to look for plant damage and symptoms. Since spider mites are so small it is much easier to spot the damage than to find a tiny mite wandering around on your leaves. Spider mites suck, literally. They have piercing-sucking mouthparts that they literally use to stab your beloved plant and suck the life from collapsing the mesophyll leaving a yellow spot behind. The result is a stippling and yellowing pattern on your leaves.
When infestations go unchecked and the population takes off you may see webbing. This webbing is how this class of mites earned the nickname spider mites! You can tell webbing of a mite apart from a spider by first looking for leaf damage and then taking a really really close look at the webs. Are there little flecks in the web? Maybe they are moving? Those are the mites!
See those little flecks hanging in the leaf gap there? Yep. Those are mites hanging out on webbing.
… Jerks.
The most common mite is Tetranychus urticae or the two-spotted spider mite (I’m going to go ahead and just use tssm for short). These mites got their name from the two saddlebag spots on their backs. Seriously, I love it when the names just make sense! They can vary in color from brownish red to greenish yellow or translucent (most common). Some people may be able to see the spots with the naked eye but most people use special tools to look at pests. The most common tool in the field is a jewelers loupe - you’re going to want to get one with at 10-30x magnification on it. If you want to take an even closer look or possibly take some photos or videos (which I highly recommend!) there are a few affordable Bluetooth microscopes out there that you can connect right to your phone. There are also clip on attachments for your phone that you can use to get macro images of the tiniest little things. It is so much fun to watch these guys on the big screen and it gives you a much better idea of what is going on with your plant. Plus, if you are ever struggling to identify a pest you are going to need to supply high quality images to an expert for ID.
This photo was taken with the bluetooth microscope and viewed on my phone. For $40 it is really decent quality and let’s you get in real close and personal with these 8 legged devils.
Notice although they are a little dark they still have two distinct patches on either side of their abdomen. Those yellow/clear round spheres? You guessed it - those are their eggs. It looks like the top right one is right in the middle of laying one!
Ouch! That’s a huge egg. I feel a little bad for her… Just a little bit.
Bonus points to anyone who can find the little larvae walking through the slide. How can you tell what that is you ask? …
So, let’s say you get your tools and take a really really close look at these guys but… you see some without spots! What is going on? Well… tssm have 5 distinct life stages and the first one after hatching from the egg is an odd one. Mites are arachnids and have 8 legs whereas insects have 6 legs but this first stage called the larval stage only has 6 legs! Further complicating things, the larval stage may or may not have the spots yet because… well… the spots are basically poop. And this youngin’ hasn’t had anything to eat.
The life cycle of the tssm is as follows:
Egg - Perfectly round spheres laid on the underside of the leaf
Larvae - 6 legged, may or may not have two spots
Protonymph - 8 legged and largely inactive - 2 saddlebag spots developing
Deutonymph - Similar to the protonymph albeit slightly larger. Last stage before molting to become…
Adult - Full reproduction capacity, two spots, baby makin’ machine
This entire lifecycle can take anywhere from 7-36 days depending on the temperature. Higher temps = faster life cycle. At a normal household temperature of 70 degrees the average lifespan of an adult tssm is around 18 days and in that time period females can lay 2-3 eggs a day. This may not seem like a lot but lets say you start out with 10 adult female mites on your houseplant. During their lifetime they would lay a collective 540 eggs. And their babies will also lay eggs… leading to exponential growth so that in one month your problem could explode from ten to thousands of mites on your plant!
Ok, so now that I’ve scared you and we’ve taken a closer look at these guys, we still hate them so how do we kill them? I have tried everything under the sun but there was one unique method that I used that worked so well that my tssm literally went extinct! And the best part is, I barely had to lift a finger let alone move any of my plants! Want to know more? See the next post: Mites: Death to all spider mites. This is war.
MYTHBUSTERS:
Myth: They will bite you - No
Myth: They are hiding in the soil - most likely no. More likely that they hitched a ride on your clothing or on a new plant you brought in.
Myth: All insecticides kill mites - no - most insecticides target INSECTS i.e. 6 legs. You need to make sure the label includes “miticide”