The 7 Worst Insects That Can Kill Your Cannabis Crops

Lots of states now allow cannabis cultivation. Whether you’re a commercial grower looking to sell your crop to dispensaries, or an MMJ patient cultivating a few plants at home, the growing process is a learning curve. Cannabis can be a finicky crop, and growing it presents some particular challenges.

There are many things to consider, including the grow room’s temperature, humidity, light, growing medium, fertilizers, and more. The checklist is a long one, but nailing it and producing a high yield of good-quality bud is worth it.

Once you have your grow up and running, threats to your cannabis plants include mold, mildew, and pests. A multitude of insects can attack and ruin your cannabis crop, including:

  • Spider mites
  • Aphids
  • Fungus gnats
  • Whiteflies
  • Thrips
  • Caterpillars
  • Slugs and snails

It’s vital to know how to recognize and protect against these creatures. In this guide, we cover how to recognize them and how to deal with them, including some preventative tips.

Why Are Insects a Threat to Cannabis?

As any cannabis user or grower will know, marijuana contains a decent load of tetrahydrocannabinol or THC. Humans have loved this plant for decades, using it both medicinally and as a way to get ‘high’; this high comes from THC.

Originally, THC may have developed as a pest deterrent. Any mammal that comes along and munches on cannabis buds will soon feel dizzy and disorientated, and they’re unlikely to come back for a taste any time soon!

Insects, however, do not appear to react in the same way. On the contrary, insects seem to adore cannabis as much as we do. Since insects multiply quickly and often move in groups, your entire crop can be wiped out rapidly if there’s an insect infestation in your garden.

That’s why it’s essential to try and prevent pests as much as possible (we have included tips for doing so at the end of this article). It’s also imperative to know how to spot an insect infestation in the event one takes place, and how to deal with it swiftly. Remember, not all insects are a threat to cannabis, but the ones that are need to be dealt with immediately.

Can I Use Pesticides to Get Rid of an Insect Infestation?

Under normal circumstances, it would be easy to spray your crop with pesticides and eliminate the problem swiftly and efficiently. However, pesticides are not always safe for consumable products such as cannabis. Even the pesticides that have been marked safe for human consumption in small quantities are not necessarily safe for combustion. In other words, they shouldn’t be used on cannabis.

What’s more, consumers these days are hesitant to use products where pesticides were used. Environmental concerns mean that you should try to avoid chemical pesticides where possible, sticking to natural methods.

Plus, not all insects will damage your crop – some insects are beneficial for your garden! There’s no point in wiping out the entire biome when some creepy crawlies are enhancing your crop. In this article, we cover some of the best ways to get rid of the harmful insects without hurting your cannabis or the environment.

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The Top 7 Worst Insects for Cannabis

#1 – Spider Mites

How to Identify Them: Small, spider-like creatures; signs include thin webbing on the plants and pale spots on the leaves.

How to Prevent Them: A colder, breezy grow room. Pesticides, organic insecticidal soaps, bleach solutions, and alcohol solutions will get rid of an infestation.

Spider mites are perhaps the most common pests afflicting cannabis growers. These awful creepy crawlies reach maturity in just one week and reproduce rapidly; once an infestation breaks out, it’s hard to control.


These mites are leechers. They drain the chlorophyll out of the plant until it dies, which is why one of the most common symptoms of a spider mite infestation is white spots on the leaves. You may also notice thin strings of webbing.

The mites themselves are miniscule, and you probably won’t notice them at first glance. They can usually be found on the underside of the leaves. Try grabbing a magnifying glass to see if you can identify them; they have 6-8 legs and look a bit like spiders.

To get rid of them, you can use pesticides like spinosad, which is organic. Neem oil also works, and you can even use a solution of 9 parts water to 1 part alcohol. This solution won’t damage the plant, but will effectively kill the mites.

#2 – Aphids

How to Identify Them: Tiny bugs with yellow wings that inhabit the underside of the leaves. Aphids can make the leaves turn yellow and wilted.

How to Prevent Them: Ladybugs, garlic water.

Aphids are another really common pest in cannabis gardens. In fact, they’re a common appearance in gardens in general.

They’re larger than spider mites, so you won’t need a magnifying glass to see them. There are several kinds of aphids, and they may be yellow, green, or black. They often have yellow wings. Worryingly, a female aphid can give birth to live young 12 times a day, so infestations quickly get out of hand.


Aphids usually populate the underside of the leaves, sucking out nutrients. The leaves thus become yellow and wilted as they are undernourished.

One of the simplest and most efficient ways to get rid of aphids is to introduce ladybugs. While these pretty insects won’t harm your garden, they will eliminate aphids. Alternatively, spray the plants with strong garlic water. Again, this is a safe and organic method.

By the way, if you see ants in your cannabis garden, you need to get rid of them. Ants will ‘farm’ aphids to collect honeydew, and they can make an aphid problem worse.

#3 – Fungus Gnats

How to Identify Them: Black bugs in the soil about 3-5mm in size; dark head with a transparent body.

How to Prevent Them: Dry out the top layer of the soil or use diatomaceous earth.

Even their name is gross! Fungus gnats are dark-colored bugs that live and reproduce in the soil. They love eating cannabis, and you may also find their larvae in water run-off. They get their name because they eat the fungus at the base of the plant and tunnel down into the root system, which spells terrible news for your cannabis plants.


Since fungus gnats live in the soil, they’re pretty hard to see. Luckily, there are preventative methods to stop an outbreak. First of all, you can place a sticky insect pad near the base of the plant, which will catch the larvae. Then, you can add a peroxide/water mixture to the area where you think the gnats are.

As for prevention, it’s a good idea to use diatomaceous earth on top of the soil. The sharp shards will shred the wings of gnats, and the dryness will dehydrate the larvae and kill them.

#4 – Whiteflies

How to Identify Them: White, winged bugs. They take flight when you touch the plant. They leave mottled spots on the leaves.

How to Prevent Them: Neem oil, zinnias, garlic mixes.

As you can probably guess, whiteflies are white flies. They are white, winged creatures. Fortunately, whiteflies are easy to spot; they cluster together in large white clouds on the leaves. If you touch the plant, they will all fly off in a large cluster.


Whiteflies damage the plants and produce a similar effect to spider mites, giving the leaves a mottled appearance with lighter spots. They can easily spread diseases, too, ruining a whole crop very quickly.

Pest management comes down to the basics: Neem oil and garlic water. Alternatively, you can introduce other plants like zinnias, which attract predators that kill whiteflies.

#5 – Thrips

How to Identify Them: Small and pale. Nymphs are wormlike and translucent. Thrips leave silver, bronze and white marks on the leaves, and the leaves may be brittle.

How to Prevent Them: Predatory mites, neem oil


Thrips are not a problem you ever want to face as a cannabis grower. They are small insects that feed on the flowers of cannabis. When they are young, thrips are pale and worm-like, but they grow more fly-like and darker as they mature. It’s hard to spot a thrip infestation and even harder to get rid of one.

These insects leave trails of white, silver, and yellow on the leaves they munch on. Some users say they look like snail trails. Thrips are another pest that can spread disease, causing a whole lot more trouble.

The best measures are preventative, with things like diatomaceous earth. Once you have an outbreak, you can use neem oil to get rid of them. Predatory mites are also a good option for dealing with thrips.

#6 – Caterpillars

How to Identify Them: Fat, worm-like creatures that are often brightly colored and patterned. They create holes in the leaves and plants.

How to Prevent Them: Predatory insects, BT spray


Most people will know what caterpillars look like and how to spot damage. The problem is that you may not realize you have caterpillars until the damage is already done. Caterpillars can create huge holes in the leaves, and borer varieties will eat the plant from the inside out. It can cause enormous damage to your crop.

Even though butterflies and moths may look beautiful, you can’t let them hang around your garden. Butterflies and caterpillars are strongly attracted to cannabis, and you don’t want them laying eggs on your crop.

Once you have an outbreak, you may need to introduce insects like predatory wasps. Alternatively, use a Bacillus thuringiensis (BT) spray. This is basically an anti-caterpillar spray, though it also kills fungus gnats and worms. However, it is generally safe for most beneficial insects.

#7 – Slugs and Snails

How to Identify Them: Grey-brown, large creatures with no visible legs; snails have a round shell. They leave glistening trails everywhere and make holes in the leaves.

How to Prevent Them: Salt, beer, predators

Slugs and snails are a common appearance in any outdoor cannabis grow. Unfortunately, they seem to like the taste of marijuana! You’ll immediately spot most slugs and snails because they’re larger than most other pests; some individuals can actually become enormous! Plus, both of these creatures leave silver, glistening trails everywhere they go.


Once you have slugs and snails, there are several things you can do. Salt is a known slug-killer, as it dries them out. Beer is also apparently a handy trick, and it can even be used as a deterrent! Be careful, though, because alcohol is flammable, so you should remove all traces of beer from the buds.

Finally, frogs and toads kill slugs and snails. If there’s a water feature nearby to attract amphibians, you probably won’t need to worry about slugs and snails.

Final Thoughts on the 7 Worst Cannabis Insects

There are lots of insects that can attack your cannabis garden; these are just seven of the most common. At the end of the day, you should always be taking preventative measures against pests before an outbreak occurs.

However, once you have pests, you should know that it’s not the end of the world; there are ways to manage insects safely and efficiently.

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