Pleurotus ostreatus infested with tiny gnats. I can see them with my loupe but too hard to photograph even though I said cheese! They have prominent attenae, and segmented bodies - but I guess that describes most insects :(

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Using uv light as the led light made them scamper away

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Maybe 1-2 mm in length. And they leave bite marks!

Here's a better picture taking using a macro lens on my mobile phone

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What can I do to eradicate them with out harming the mushrooms? In the first instance I've removed the substrate from the bag, and sprayed with a mist of water to try and wash them off. This must be the 4 or 5 flush from the culture!

Edit: looks like the infestation, or treatment, was enough to cause all of these mushrooms to abort.

  • Are they 6 or 8 legged? The animal to the left (with antenna pointed downwards) in the magnifying glass looks like a springtail (Collembola), but can't see what species. Do they jump? They are detritivores, so unfortunately they will probably damage your crop.
    – benn
    Jan 2, 2018 at 10:24
  • Are these the mushrooms you're growing on coffee grounds? If so, what did you mix the coffee grounds with and did you sterilize them first? They are apparently extremely prone to 'contamination' whatever that means....
    – Bamboo
    Jan 2, 2018 at 12:22
  • I'm interested in this grow, also. It looks like it is on wood chips. And those are unusually elongated pleurotis - was the bag completely sealed until pinning? This would lead to too much CO2, which could cause such elongation.
    – That Idiot
    Jan 2, 2018 at 16:44
  • No coffee. It's straw inoculated with grain spawn. Coffee is prone to contamination with Trichoderma harzianum. These insects don't jump, they run. But they might be juveniles since I've also seen some flying ones. Etoliated since I left the cover on of the aquarium I'll using as a grow chamber. I'm going to add more oxygen now! Jan 2, 2018 at 17:17
  • If they can fly, they are not springtails. Springtails are wingless hexapods.
    – benn
    Jan 2, 2018 at 17:24

2 Answers 2


Judging from the new picture, they are springtails. Check this here, they look very a like.

Springtails are not insects, however they have six legs (Hexapoda), so they are related. In an evolutionary tree they are placed somewhere between insects and crustaceans. They like moist and humidity, so spraying them with water might not chase them away.

I did my PhD study in molecular (soil) ecology, with focus on springtails. They are very important for a healthy soil ecosystem, and they eat fungus and other rotting material. (In laboratory we fed them grains of baker's yeast, which is also fungus). Of course in your case, when growing mushrooms for consumption, they are a pest! I have no experience with getting rid of these animals, but in this pdf they have some options how to get them off your mushrooms.

  • We use a hose to get rid of aphids. So, I'm using a high pressure spray from my mister to knock them off into the sink! The last time I had this problem with the same media, I used ethyl alcohol to spray them but it also killed all the developing mushrooms! But they have recovered enough for this current flush to appear. Of course I can't reduce the moisture as that would kill the mushrooms. Jan 2, 2018 at 19:58
  • Were did the springtails come from? The media that the grow kit came with? Jan 3, 2018 at 2:39
  • Usually they enter via plant pots (soil). But I think in your case it could definitely be the media. Does it contain dung or other organic matter?
    – benn
    Jan 3, 2018 at 8:04
  • No, it was just pasteurized straw when I got it. That's why I thought it must have flown in from somewhere. And the growkit plastic bag had a micron filter on it which I thought you only used when sterilizing media. Jan 3, 2018 at 17:51
  • It sounds like they didn't come with the media then. Maybe they crawl in from outside or via plant pots? Hard to say.
    – benn
    Jan 3, 2018 at 20:05

They are most likely fungus gnats.

Here is another place to start reading about them.

They ARE treatable, and need to be treated or you'll have larvae all through the mushrooms. However the best way to deal with them is by avoiding them in the first place - which can be difficult. Many people use fine mesh - like mosquito netting - to protect their crop before pinning even starts.

  • The animals in the pictures seem rather wingless, but maybe because of the insufficient zoom quality?
    – benn
    Jan 2, 2018 at 13:43
  • could be their larva? but then they wouldn't have antennae. But if it is small bugs on mushrooms, typically it is fungus gnats.
    – That Idiot
    Jan 2, 2018 at 15:42
  • 1
    Fungus gnat larvae are not black, but more transparent. Adult gnats have wings. I think they are more likely either springtails (if they have 6 legs) or mites (if 8 legged). They are also common mushroom pests.
    – benn
    Jan 2, 2018 at 15:54
  • 1
    @b.nota - I like the springtails idea. I hadn't realized they were common mushroom pests.
    – That Idiot
    Jan 2, 2018 at 16:41

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