Generalist · Spider Mites
Amblyseius andersoni
The all-weather one. Patrols for spider, broad and russet mites and keeps hunting from 43°F to 100°F, so a room whose temperature will not sit still does not stop it.
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How much, and how often
Two questions — how bad it is, and how many plants. You get a size and the dates to put it out.
How bad is it?
Pick the one that sounds like your room. If you are between two, take the higher.
How many plants?
Six-inch pots. Count a large specimen with a dense canopy as three or four.
Your size and schedule
More about this dose
The three things people ask once they have their size. Open any of them.
Am I light, moderate or heavy?
Light
- You had to turn a leaf over to find it — a few pale specks, or one rough patch you were not sure about.
- No webbing, and no twisting in the newest growth.
- New growth is coming in clean.
- One or two plants. The rest of the shelf is fine.
Moderate
- You notice it walking past, without stopping to inspect.
- Fine webbing where a leaf meets the stem, or new growth starting to curl.
- Leaves feel rough or look bronzed rather than simply dusty.
- A few plants in the same area have it.
Heavy
- You saw it from across the room — whole leaves pale, bronzed or distorted.
- Webbing strung between leaves, or growing tips twisted and stunted.
- New leaves are coming in already marked.
- It has reached plants that were never touching.
Overshooting costs you very little — andersoni holds on pollen when prey runs short, so a heavy dose on a light problem simply stays on as a standing guard. Under-dosing costs you the round.
Pest mites are built to be underestimated:
- Damage is a record, not a reading. Stippling and bronzing are scar tissue. They stay on the leaf long after every mite that made them is dead.
- Most of them are too small to see. Broad and russet mites are invisible without a loupe, so you are reading the damage rather than counting the animal.
- It travels before it shows. Plants touching an obviously bad one are usually already carrying it.
Why more than one round?
Putting it out
- Rotate, don't shake. End over end, gently, so the mites are spread evenly through the carrier before you start.
- Spread it wide. Andersoni patrols rather than swarming a hot spot, so even coverage suits how it hunts.
- Work the upper third. New growth is where broad and russet mites do their damage, so that is where the predators should land.
- Undersides too. Spider mites feed under the leaf, so tip some carrier there rather than onto the top surface.
Everything else is optional. Get these four and the release has done what it can.
A cleaner way
On a display plant, tip small piles into bio-boxes or paper cups hung in the branches instead of dusting the foliage. Same dose, nothing visible on the leaf.
The failure is forgetting. Very few programs fail because the mite underperformed. They fail in week five, when the plants look fine, the reorder does not happen, and the population holding the line ages out with nothing behind it.
A schedule is the same decision, made once. A bottle when it looks bad, then another when it looks bad again, is already a rhythm — just one you have to remember at the exact moment the plants look fine.
Change the size or the frequency, skip a box, pause or cancel from your account at any time.
Is this the right beneficial for your problem?
Five questions, in the order a grower actually asks them: what have you got, is this the answer to it, what will it eat, how does it do the killing, and will it survive your room.
Is this your pest?
Andersoni treats three kinds of mite, which is why it is usually the one to reach for when you are not certain which you have.
Three different problems look like three different things. Spider mites stipple the leaf from underneath and string fine webbing. Broad mites twist and harden the new growth until it comes in deformed. Russet mites bronze the leaf and roughen it, with nothing visible on it at all.
Andersoni takes all three — two-spotted spider mite colonies, and the microscopic ones that most predators miss: broad mites and hemp russet mites. It picks off thrips larvae and whitefly eggs along the way. If broad mites are the whole problem, Amblyseius cucumeris is the one with the published record; andersoni is what you use when you cannot narrow it down.
Then: is andersoni the right answer to it?
Choose this if
Choose andersoni for a space you cannot climate-control, and for a mite you cannot identify. It is active from 43°F to 100°F with no winter dormancy, so a cold snap or a heat spike does not stop it, and short days do not send it into diapause the way they do other species. It also feeds on pollen, so it stays on a clean plant as a standing shield rather than dying out.
Choose something else if
Its advantage is tolerance, not appetite. Against heavy webbing on an outbreak already spreading, Phytoseiulus persimilis is faster and you should lead with it — use andersoni behind it to hold the ground and cover the cool end of the year. And in a stable, warm, humid room, a specialist will out-eat it.
What it kills, and what it won't
It also feeds on pollen, which is not a pest — it is how the population holds on a clean plant between outbreaks instead of starving out. That is what makes it a shield rather than a one-off treatment.
How it works
What it does to the pest, what it does on the plant, and what that leaves you looking at.
It patrols rather than swarms
Andersoni is a predator — not a poison, not a repellent, nothing systemic. It works across a plant rather than piling into one hot spot, which is why even coverage suits it and why it finds the microscopic mites hiding in growing tips that a colony-hunter walks past. No residue, no re-entry interval, and nothing it eats can develop resistance to being eaten.
It keeps working when others stop
The range is the product. From 43°F to 100°F it keeps hunting, most actively between 65°F and 85°F, and it does not die off in a temporary cold snap or a heat spike. Short days do not put it into dormancy either, so a winter indoor grow or a late outdoor season still gets a working predator.
Pest numbers, not mites
You will rarely watch this happen. They are under half a millimetre and beige, and they work on leaf undersides and in the growing tips. Judge it the way a grower does — new growth that stops deforming, stippling that stops spreading — rather than by trying to count predators on a leaf.
It is not a knockdown. The damage already on a leaf is permanent and stays there whatever happens next. What changes is the growth that comes after — which on a broad mite problem is the whole point, because deformed new leaves are the symptom you are buying this to stop.
Will it work in your room?
If you already have heavy webbing and a colony spreading, this is not the fast answer. Lead with Phytoseiulus persimilis and put andersoni in behind it. And if what you want is a standing population rather than a dose, the slow-release sachet is the better buy.
About andersoni
A predatory mite about half a millimetre long that hunts on leaves. It has no interest in your plant and no interest in you — it eats other arthropods, and when there are none left it eats pollen until there are.
New to beneficials?
Five things that catch almost everyone the first time.
After you release it
What actually changes, how fast, and the three things this one does not reach.
How you'll know it's working
Existing damage does not heal. A leaf that came in twisted stays twisted after every broad mite on it is dead, because that is scar tissue and not an infestation.
So judge by three things instead: new growth that stops deforming, stippling that stops spreading, and — because andersoni holds on pollen — some population still on the plant a month later.
Gradual by design. Andersoni is the tolerant one rather than the fast one, so expect the trend to turn over two to three weeks rather than in a few days.
Getting it to you
What is in the bottle, how it travels, and what happens if it arrives wrong.
What arrives
Loose mites through a bran carrier, mixed stages. All of it beige and under half a millimetre, so trusting the label is part of the deal. The carrier goes out onto the plant with them.
You are unlikely to see movement, and that is normal for a mite this small against a pale carrier. It is not a sign that anything is wrong.
Release on arrival. There is no holding option for loose mites — open the bottle the day it lands.
When it ships, and when it lands
Shipping
We ship when they're ready to travel. Live orders go out Monday to Thursday. If a colony needs a beat to peak, or we're propagating a fresh batch, yours might hold up to a week. All mites and insects ship 2-day or Overnight depending on what's best for them.
When it lands
Open it that day. Spread it wide rather than piling it on one plant, and tip the carrier onto the leaf undersides and into the growing tips where these mites actually feed.
About the ones that don't make it
Some of them die on the way. That is why we send more than you paid for.
A predatory mite is the size of a grain of table salt. It ships in a bottle, in a van, for two days.
Roughly 15% will not survive that. We cannot prevent it, so we price it in: the number on the label gets counted out, and then the cushion goes in on top of it.
Your 500-mite bottle leaves here holding more than 500. The dead ones are already paid for.
If you can see them
Ladybugs, lacewing larvae, Orius — the minute pirate bug — and the beetles. Tip a few onto white paper and give them twenty minutes at room temperature before you judge anybody.
Cold insects are genuinely good at playing dead. The deceased have been known to get up and walk off the counter.
Still more than about one in seven not moving? Photograph them and file a report.
The photo is not us doubting you. It is how we tell a bad batch from a bad courier day from a mailbox that hit 104°F.
If you can't see them
Mites, nematodes, eggs — most of what we sell, this one included. A bottle of carrier looks the same whether it holds 500 live mites or none, and no photograph settles that. So we don't ask you to take one.
You file the report and our entomologist takes you through the diagnostic instead — the tap test on dark paper, where the box sat, what your room was doing, and then what the pest is doing about ten days later.
Seventy-two hours from delivery, either way, with your order number. Replacement or store credit, your pick.
What it does not reach
Three gaps this page has already named, and the beneficial that closes each one.
Andersoni sachets
The bottle is the dose. The sachet is the colony — mixed stages breeding inside, releasing onto the plant for weeks. If you want andersoni still working next month rather than only this week, that is the form it takes.
Phytoseiulus persimilis
Andersoni holds ground; it is not a knockdown. Against heavy two-spotted spider mite webbing persimilis is faster, and the two work well together — persimilis into the hot spots, andersoni across everything else and staying on afterwards.
Amblyseius swirskii
Andersoni picks off thrips larvae and whitefly eggs along the way, but that is not what it is for. In a room that stays reliably warm through the summer, swirskii does more per dollar on those two.
Two cheap things that make the rest work harder. Blue cards give you the dated count this page keeps asking you to read. Breeder's Blend is pollen and Artemia; it keeps the population fed through the lull when prey gets scarce.
Questions
Can I use Andersoni outdoors?
Yes! It holds up in outdoor orchards, vineyards, and gardens because it can handle wind and temperature changes.
Will they eat my plants?
No. They are strictly predators and do not damage plant tissue.
Can I use them with other mites?
Yes. They work perfectly alongside Swirskii or Persimilis to provide a multi-layered defense.
How long do they live?
Adults live for about 3 weeks, but if food is present, they will breed and establish a permanent population.
Does Andersoni work on Aphids?
No. While they may eat a very young aphid occasionally, they are not an effective control for aphid outbreaks.
Is it safe for my pets?
Yes. These mites are harmless to humans, dogs, cats, and other animals.
I had spider mites. I added this and they got worse! All my hopes are gonna burn with my plants. This colony has got to go
Hi Bakedj, thank you for the feedback, and we're sorry the mites have been winning so far. Spider mites reproduce fast — there's a point where they can nearly double day over day. If your beneficials arrived right as that surge hit, and the dose was matched to the smaller population you had before it, they'd be behind from the start and stay behind, since predators don't breed as fast as the mites do. Plenty of other things can play a part too — a sudden temperature swing or leftover pesticide residue can knock beneficials back — but the one thing that's true is this isn't lost yet. If you'd like help diagnosing what happened and figuring out where to go next, we're glad to talk it through. Our customer service team is at info@fgmnnursery.com.
Amazing customer service
This was my first time buying bugs. I used their find a bug search which had me put it the type of infestation and the type of environment the crop is in. They pointed me to the bugs I needed and shipped out the following day. The bugs showed up in the morning next day deliver for the predatory mites. There was a mix up on the amount of mites they sent, sent out they missing containers the next day.
It’s been a few days and the predatory mites have laid a beat down on the two spotted spider mites and should save me from having to spray anything while I flower.
I will be returning every season. They even have bugs to get after caterpillar.
I honestly can't tell because it seems like the spider mite damage continues . My humidity is very high when the lights are on so maybe it decreased the ipm mites.
Hi! When you say 'very high humidity' how high is that? Andersonii performs best 40%-80%, with 80% being the highest they will tolerate. Is it possible your humidity is too high?