There are only two main mushroom pests that will wreak havoc on your mushrooms. The Phorid fly and the Sciarid Fly (aka fungus gnat). Both of these flies will lay eggs in the holes of the bags. After the eggs hatch, the larvae roam inside the substrate and quickly devour the mycelium inside. Eventually eating through the stem of the mushroom they emerge as flying adults via tiny pinprick looking holes, out the top.
looks similar to a fruit fly or sandfly. It is often seen around the soil of damp pot plants. Its larvae are tiny white wiggling maggots, Sometimes they are hard to see without a magnifying glass. More info en.wikipedia.org/wiki/Phoridae
Has long legs and a slender body so looks more like a mosquito. Its maggots are much larger so generally easier to spot. They are white, plump and often with a blackhead.
If you have the bags inside, these pests are not usually a problem unless you have pot plants already infested, or a problem in the garden outside the window. If you are growing outside you have a high chance of meeting them. More info en.wikipedia.org/wiki/Sciaridae
We use yellow sticky fly traps that you can buy from garden centres or hardware stores. These will catch the adult flies, breaking their breeding cycle. The traps are useful, and they provide a good indicator of having a problem or how big the problem is. If you are inclined to use sprays, use organic ones containing Pyrethrum. These are more for management before you have a problem, as they may not cure a massive infestation.
Firstly, don’t panic, they may look gross but are not harmful… to us at least. They have happily been munching on a diet of mushrooms inside an essentially sterile environment. They are very common inside wild foraged mushrooms. In the future, they may even end up on the plate as a form of future protein.
Less of a problem, unless it’s growing outside, are snails and slugs. They seem to seek out mushrooms and devour entire clusters overnight.
Note: Although it is still possible, I have not seen any evidence of rodents, chooks/ducks (or our little pig) showing any interest in eating our mushrooms.
Factoid: These last two articles are from PennState University. Pennsylvania has a massive mushroom growing industry, hence very solid research.
Have other problems with your mushroom grow? Here’s our article about the two most common issues: https://mycobio.co.nz/knowledge-base/if-it-hasnt-gone-as-expected/