Homegrown with Jim Berry: Beneficial Bugs for Cannabis Plants

October 22, 2026
By Jim Berry

This recipe was first shared in the Concentrates edition of Fat Nugs Magazine

Hey, folks! Welcome back to my basement. Watch your head!

Today, let’s talk about bugs. I have always been a very anti-bug person. As a kid, if any sort of anything with more than four legs entered my space, I would freak out. I’m sure it was entertaining to watch, but not a great trait for a gardener.

Experience and my love for the plant have chilled me out quite a bit. I am still not a big fan of anything crawling on me, but I have learned a tolerance and appreciation for the role many of the creepy crawlies play in cannabis cultivation.

Keeping The Right Bugs In and The Wrong Bugs Out

Winter is generally a time when the indoor home grower can breathe easier about pest infestations. Sure, you may get something sneaking in with your substrate, or you may catch something from the clone you got in the mail from that guy in California that you used to trust. But winter is a time when I’ll let down my guard about pests.

Once May hits, life outside is popping. It’s time to start taking more precautions when entering my grow space and to start scouting diligently for signs of bugs that may have found their way in from my yard.

I live on the cold side of Zone 6 and grow inside. In my garden, there have been spider mites, western flower thrips, and whiteflies. Spider mites were definitely the worst, but there are more invasive species out there— root aphids, russet mites, and broad mites, to name a few.

Pest infestations are the worst. But spraying conventional insecticides on cannabis is usually a bad idea, especially during the flower cycle. This is why many growers choose to control pests with other creepy crawlies, or beneficials, as we usually call them. Before cannabis cultivation was common, there was already an entire industry of bug producers, serving the food and ornamental cultivators.

Beneficial Bugs for Cannabis Plants

Nematodes

Nematodes are parasitic worms that live in the substrate and are generally considered pests. But one specific species of nematode, known as “SF” (steinernema feltiae), is very helpful in controlling both fungus gnats and thrips. Gnats lay their eggs in the soil, where they also spend the larval stage of life.

Nematodes will actively hunt these larvae. They penetrate the insect’s body and release a bacteria that eats the gnat from the inside out within a few days. Thrips actually lay eggs on the underside of leaves, but will spend the prepupae and pupae stages of their development in the substrate, where the nematodes control them in the same way. To apply nematodes, you would typically water them into your soil every couple of weeks or so.

Mites

Predatory mites, or Stratiolaelaps scimitus, are the most commonly deployed control in cannabis cultivation. They are tiny arachnids that feed on fungus gnats, thrips, and root aphids. They live in the soil and like warm, moist environments. If the substrate gets too dry or cold, they will struggle to survive. They are a great tool for preventing infestations, but once one has occurred, they “mite” not be able to keep up with it. Predatory mites, or “strats,” are applied to the substrate surface every couple of weeks.

Cucumber mites (Neoseiulus cucumeris) are another commonly deployed arachnid used to hunt thrip larvae before they can reach the soil. They also live above the surface, in the foliage of the plant. Because of this, they should be deployed every week or two through sachets. They look like tiny doorhangers, hung directly on the plant or trellis. They are shipped as a live colony, hundreds of mites in each sachet. They show up hungry, already breeding and ready to work.

As I mentioned, two-spotted spider mites are probably the worst pest that I have had to date. They love warm cannabis rooms and have a very rapid reproductive cycle. They will feed on leaf surfaces, sucking out the plant’s sap, while laying their eggs along the way. Left unchecked in a warm room, they can quickly get out of control.

If you use beneficials to control them, the gold standards are other predatory mites—namely, persimilis and neoseiulus californicus. Both species will actively eat both the eggs and adults alike. In the case of persimilis, they can eat up to 20 mites or eggs a day. Both of these species are deployed through sachets every couple of weeks. Persimilis are generally faster to react and are more effective, but are harder to establish than californicus, and like a more humid room.

With all of these measures, the bugs will become ineffective or die if the environment falls outside of a range of temperatures and humidity. But then, so will many of the pests, and your plants won’t be too happy about it either.

The Limits of Fighting Bad Bugs with Good Bugs

These are the most common beneficial bugs used in cannabis cultivation. There are many others that can be used that may be better suited to the environment or to handle more specific, less common pests. I have even released lady beetles in my room. I didn’t find them very effective at controlling spider mites—mostly, I was just cleaning up dead lady beetles. But having a few in the room is fun and makes for good photographic opportunities.

Beneficials can be very effective at preventing and treating an outbreak of pests. But they have their limits. If an outbreak becomes too severe, they won’t be able to keep up. If they don’t have enough to eat, they will die, and populations will need to be replenished.

Beneficial bugs are almost always applied continuously as a preventative. But depending on where you grow, you may have to rely on a couple of different strategies and benefits to control a specific problem.

You’ll likely have to order them from major suppliers on the web, unless you have a very competent grow shop or garden center in your neighborhood. Beneficial bugs typically have to be shipped overnight or 2nd day air, at least. These suppliers don’t structure their products with the homegrower in mind, so you’ll often pay too much for a larger population than you need, because these products have no shelf life.

Using them continually can get expensive. But I would much rather pay that expense than use most foliar products (or worse) in my flower room.

Benefitting from Beneficial Bugs

If a new grower is interested in beneficials, I would recommend they start with nematodes or a few sachets of cucumeris. This will help prevent and control fungus gnats and thrips, which are the two most ubiquitous pests when growing cannabis.

From there, be vigilant about scouting and preventing new pests from getting into your garden on your person. If you have a pest pop up, make sure that you properly identify the pest to ensure that you’re treating the right problem. If it lives above ground, those sticky cards are excellent at trapping pests, helping you to identify them. Once you’ve identified the pest and researched a bit, you can decide whether you’d like to attack it with other bugs.

If you choose to use foliar sprays, please, please, please make sure that it is safe for cannabis. If you’re in veg, make sure that the product is not systemic, meaning that the plant won’t absorb the pesticide into its vascular system (much like us taking an oral antibiotic).

With very few exceptions, you should not spray anything on your flowering plants. Cannabis is one of the only agricultural products that is often smoked, and we need to hold it to the highest standards when it comes to the chemicals that we use in its production.

From my experience as a home grower, you will usually be better off cutting your losses and starting over from a pest infestation, with a complete sanitation of your space in between. It is a lot of work and a little heartache, but a hard reset is much better than living with pests forever.

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