If you notice a fine webbing between your bonsai plant leaves you may have spider mites.
Outdoor bonsai such as Juniper are more susceptible to this than indoor bonsai.
Spider mites can be seen with the naked eye.
Inspect the web to see if you see movement.
They will look like very tiny spiders or micro spiders as I like to call them.
Why they are bad for your bonsai Spider mites feed off of your bonsai using their tiny mouth parts to suck out the plant cell contents.
You may notice white or yellow areas in your foliage as a result.
Leaves may fall off as a result of the damage.
Your bonsai may lose its color, have its growth stunted, or die as a result of the damage if there are a significant amount of mites.
Life Cycle Spider mites hatch from eggs laid on the bonsai.
They generally hatch into larva within the first 3-7 days after being deposited onto your bonsai.
Prevention Carefully inspect any new bonsai purchases for mites by looking at the tops and bottoms of their leaves.
They are about the size of a period on a typewriter and can be introduced from contaminated soil as well.
Treatment Predators If you would like to control the situation naturally, introducing predator insects such as ladybugs, lacewings, and predatory mites are your best solution.
Pesticides If you go the pesticide route, make sure you get a miticide.
Insecticides that aren't specifically miticides don't work very well on spider mites.
Conclusion Spider mites can be detrimental to your bonsai, but if caught early the damage will be minimal.