Friday, 26 July 2013

Two-spotted Spider Mite

Image: Gilles San Martin
Tetranychus urticae
It's not a pretty sight when a mite gets mighty...

If you love plants or are among the small community of plants who read this blog (hi, Jurgen!) then you know exactly where you are when the Red Spider Mites come to town. It's called World of Trouble, and it's one of the less successful theme parks due to their appalling health and safety record.

Image: Gilles San Martin
Can you see that strand of silk? That's why they're Spider Mites
You might not know where the Spider Mites are, though, since they're only about half a millimetre (1/50 in) long. This is what "next to nothing" was coined for.

Image: Gilles San Martin
Their usual colour. Plus one of their eggs. It's huge! Relatively
It's even worse than that because for most of their life they're a bit green and a bit transparent, which is the perfect colour and lack colour to help them disappear into the leaves they live on. They spend their time using their tiny, piercing mouthparts to break into plant cells and suck out the contents. Then they move on to next cell. You know you're in a different world when you eat your salad one cell at a time!

Unlike all sorts of other mites and aphids who are so reliant on particular plants they get named after them, the Two-spotted Spider Mite is able to feed on hundreds of different plant species, including tomatoes, potatoes, corn and roses. They eat our staples, our salad and our flowers! The audacity!

Image: Gilles San Martin
Covered in sensory hairs and two red eyespots
What do they do with it all, you ask. Obviously they live on some of it and pass the rest out... we all do that. So I guess you didn't ask at all. But the strange thing is that the waste products are clearly visible through their transparent body. It's the two, dark spots they're named after! Ick... perhaps they should have stuck to eating only tomatoes so they could be the Tomato Spider Mite or something.

Image: Gilles San Martin
A male. He's a little slimmer than the females
This voracious appetite for all things green has enabled the Two-spotted Spider Mite to travel the world and sample exciting, new cuisine. While they were originally a European species, they can now be found just about everywhere. If the seasons turn cold, the females will turn red and delve into nooks and crannies to hibernate, ready to lay lots of eggs in the Spring. So you won't catch them out with a chilly winter, either.

You might think "so what?" It's a tiny mite eating plant cells. Give a mite a leaf and you feed it for a lifetime, I can deal with that.

Image: Aleksey Gnilenkov
Some
The problem is numbers...

Image: Aleksey Gnilenkov
Many
Big numbers...

Image: Aleksey Gnilenkov
Earth was nice while it lasted
Gigantic infestation numbers!

Plants can become lost beneath a squirming red carpet of Spider Mites reminiscent of the Christmas Island Red Crab. These are Spider Mites, so they also produce silk that protects them from predators and bad weather. They can also use their silk to walk across from one plant to another.

If they're feeling adventurous or far too crowded they can release a long strand of silk so it catches the wind. With a bit of luck they can travel for miles o'er hills and dales, forest and meadow; onward across town and country, life splayed out before them, beneath them in all its minute pettiness and scarcely perceptible mock-grandeur before they land right in your rose bush.

Image: Gilles San Martin
If the temperature is right, Spider Mites can go from egg to adult in under a week, passing through a 6-legged larval stage and two nymph stages to get there. If the temperature is not optimal it can take closer to 3 weeks. Either way, the females may live for another month or so and lay several hundred eggs in this time. She'll get to see them grow into strapping young mites; maybe she'll meet a few thousand of her grandchildren!

With this amazingly fast growth rate and huge numbers of eggs, Spider Mites are apt to become immune to all sorts of pesticides. They're built to survive, travel, feast and infest. Makes you wonder how the rest of us have managed to survive so long.

6 comments:

TexWisGirl said...

no, i do not like hairy little mites!

Joseph Jameson-Gould said...

Not to worry, they're so small you'll barely ever see them!

Still there though...

Daniel Berke said...

They're kinda cute. Not sure how I'd feel seeing them in those gigantic infestation numbers though.

Joseph Jameson-Gould said...

I know! It's definitely possible to have too much of a cute thing!

elfinelvin said...

Had some on a house plant once. I just kept wiping them off till they stopped showing up. Who eats them?

Joseph Jameson-Gould said...

That's one way of stopping them if you can get in early enough. Their chief predator seems to be another mite called Phytoseiulus persimilis:

http://www.biocontrol.entomology.cornell.edu/predators/Phytoseiulus.html

It often seems to be the case that a mite is a mite's worst enemy!

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