Are Mealworms Good For Compost Or Are They Bad?

Are Mealworms Good For Compost Or Are They Bad?

In previous articles, I’ve written a lot about composting and the benefits that this adds to your garden. I’ve also covered the different methods of composting but have recently come across the question “Are mealworms good for compost?”.

Now, I understand that having ordinary earthworms such as red wigglers in your compost is definitely beneficial and I often find these in my own compost bin, I have never thought about mealworms.

All I really know about mealworms is that they’re often available at a pet store as food for reptiles, rodents, fish and birds. This is because they’re a high source of protein for these animals.

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I also have friends who fish and they will sometimes use mealworms for bait.

Adding them to my compost has never crossed my mind, so I decided to do some research to see if there are any actual benefits to this.

Here’s what I found.

What Are Mealworms?

close up of a mealworm

Contrary to their name, mealworms aren’t actually worms. Rather, they’re the larvae of the darkling beetle. The majority of insects go through a number of life cycles or stages before they reach maturity.

The darkling beetle (Tenebrio molitor) is not dissimilar. When the adult beetles lay their eggs, the larvae will emerge from these eggs. These larvae are known as mealworms. 

Mealworms work their way through lots of organic matter until they’re ready for their next life stage. This could take anywhere from 6 weeks to several months.

Once the larval stage is complete, the larvae will pupate before emerging as fully-grown beetles.

If you have these beetles in your garden, you might find that you will discover some mealworms in your compost as they chomp their way through all the organic plant matter in there.

On the other hand, the larvae in your compost might be black soldier fly larvae instead. So, how do you tell the difference?

How Do You Distinguish Mealworms From Black Soldier Fly Larvae?

two images - a group of mealworms, a group of black soldier fly larvae

Both the mealworm larvae and the larvae of the black soldier fly look very similar. Therefore, you might want to distinguish them from each other so that you know exactly what is working its way through your compost.

Black Soldier Fly Larvae

Black soldier fly larvae are pale beige in color and have dark rings around their bodies. As they start to mature, they’ll turn to a dark grayish brown. If you put one side by side with a mealworm, you’ll find that the black fly larvae are thicker and shorter than the mealworms.

These little critters can work their way through a huge amount of organic matter but won’t leave any castings behind.


On the other hand, mealworms are lighter brown to yellow in color and quite long and thin when compared to soldier fly larvae. Mealworms tend to look more like small caterpillars and reach a length of up to 3cm.

They will also consume a huge amount of organic matter as well as dead insects. The difference is that meal worms do leave behind mealworm castings which are commonly referred to as frass.

Mealworm frass contains a good amount of essential plant nutrients such as nitrogen, phosphorus and potassium. It looks somewhat similar to dry sawdust. 

Frass is also commonly available as a fertilizer for your garden and is labeled as mealworm compost. One of the benefits of using this is that it contains a lower amount of water-soluble phosphorus. 

This is particularly useful in reducing the amount of fertilizer runoff that might end up in local waterways and poses a threat to the natural ecosystem.

All of this would suggest that mealworms are indeed good for compost. But, before you rush out to purchase some mealworms to add to your compost bin, let’s further investigate the pros and cons of adding mealworms to your compost.

What Are The Benefits Of Mealworms In Your Compost?

two hands adding frass to a compost bin

So far, we’ve discovered that mealworms are happy to munch through lots of organic material and that they leave behind nutrient-rich castings that will help to fertilize your plants. So, here’s a roundup of the benefits of having mealworms in your compost.

  • Mealworms will feed on all the decaying matter in your compost bin.
  • Their castings, commonly known as frass, are a nutrient-rich fertilizer for your plants.
  • Apart from food scraps, mealworms may also consume other materials such as styrofoam.
  • Mealworms reproduce at a fast rate as one female darkling beetle can lay around 70 to 100 eggs at any one time.
  • If you also have backyard chickens or keep other pets such as reptiles, the mealworms in your compost provide a handy food source for these.

While these advantages all sound great, are there any cons to having mealworms in your compost?

What Are The Disadvantages Of Having Mealworms In Your Compost?

an adult darkling beetle on a flower bud

As is the case with most things in life, with advantages or benefits, there will usually be a few disadvantages that you need to consider. Here’s the rundown on the cons of having mealworms in your compost.

  • Mealworms prefer a cool environment. This means that if you find them naturally in your compost, it will not be hot enough to destroy bacteria and other organism that might be harmful.
  • The frass generated by mealworms is not nearly as nutrient-rich as the castings that are produced by earthworms.
  • It may be necessary to supplement the mealworm’s diet with other products such as wheat bran or grains.
  • Once the mealworms are ready to pupate, they won’t be of any further use in your compost.
  • If your compost bin doesn’t have a tight-fitting lid, the presence of mealworms could attract unwelcome visitors such as rats and mice.

Personally, when I weigh up the advantages with the disadvantages, mealworms don’t add enough benefit to consider adding them to my own compost bins.

Plus, because my bins have tight-fitting lids, it’s unlikely that the beetles will find their way into one of my compost bins on their own.

And, what about those beetles? Can they be a problem in your garden?

Can Darkling Beetles Pose A Problem In Your Garden?

Adult darkling beetles can actually pose a threat to your garden because they like to feed on young plant growth. Therefore, if you’re often planting young seedlings into your veggie patch, you certainly don’t want an overabundance of these beetles in your garden.

This then brings us to the question of black soldier fly larvae. Do these add any benefits to your compost?

Are There Pros And Cons To Having Black Soldier Fly Larvae In Your Compost?

a black soldier fly on a leaf

There are indeed pros and cons to having black soldier fly larvae in your compost but I personally would not encourage this as I believe there are much better solutions.

However, if you do happen to accidentally find these in your compost here are the pros.

Benefits Of Black Soldier Fly Larvae In Your Compost

  • These larvae will consume a huge amount of organic matter and kitchen scraps that you add to your compost.
  • They can consume things not recommended for backyard compost such as meat, dairy products and fish.
  • They can easily speed up the composting process due to their voracious appetites.

Disadvantages Of Black Soldier Fly Larvae In Your Compost

  • If you have an open compost pile and not a closed bin, using black soldier fly larvae can create an increase in the offensive odor given off by the composting material.
  • These larvae will be almost impossible to eradicate once they’ve made their home in your garden.
  • The larvae are not compatible with any earthworms that might be in your compost because they will just crowd them out.

Once again, I certainly wouldn’t be encouraging these critters to take up residence in my compost because I far prefer the earthworms that do a good job and the compost bins I use are quite efficient at producing good compost reasonably quickly.

However, there are gardeners that breed these larvae in order to efficiently get rid of green waste. Especially, if you have a lot of scraps like meat and dairy products that you want to get rid of.

In this instance, I would suggest having a separate compost bin for this. Better still, why not invest in an electric composter that you house in your kitchen to help reduce this type of waste into garden-ready compost in no time without the use of any critters? 

You can read more about these in this article I wrote about composting in an apartment without worms.

How To Get Rid Of Mealworms That Have Made It Into Your Compost Heap

a person tipping dry leaves onto a compost pile

If darkling beetles have found your compost and have managed to lay their eggs, you might want to get rid of them so that you don’t end up with an extended family of beetles munching on your young plants.

The best way to do this is to increase the heat in your compost. If you have a compost bin, add some more brown materials to your compost such as dry leaves, straw and even torn-up bits of cardboard.

This will increase the carbon level in the compost which will raise the heat and speed up the composting process. 

You can also bake your compost by spreading it out in a thin layer in direct sunlight. This will not only kill the mealworms but it will also kill any bacteria that might be present in your compost. 

Plus, another benefit of doing this is that the wild birds that visit your yard will most likely get rid of all the mealworms for you. Many insect-feeding birds find mealworms a real treat.

How To Prevent Flying Insects From Getting Into Your Compost

One of the best ways to prevent flying insects from getting into your compost is to use a bin with a tight-fitting lid like the static compost bins I wrote about or even the compost tumblers that are so popular right now.

These bins are so much more effective and easier to use than the compost piles that have to be turned on a regular basis. Plus, you have the advantage of placing one of these in a sunny spot somewhere out of the way in your yard.

Frequently Asked Questions

Do mealworms eat plants?

Although mealworms that have made their way into your garden prefer to feed on fallen leaves and other garden debris, they are perfectly capable of feeding on your plants, especially young seedlings.

How can you keep darkling beetles out of your garden?

Not using mealworms in your compost is a great way to keep darkling beetles out of your garden. You also want to clean up fallen leaves and other garden debris that the beetles might lay their eggs in. Placing your compost bin far away from your main growing area will also help.

Do mealworms bite?

It’s not possible for a mealworm to bite you because its jaws and mandibles are too small. 

Final Thoughts

While finding a few mealworms in your compost is not necessarily a bad thing, you have to remember that the population can grow quickly and then you might end up with a garden full of darkling beetles that can pose a threat to your seedling crops.

Although mealworms can have some benefits to your composting process, the disadvantages far outweigh the benefits in my opinion. Therefore, I would never consider adding them to my compost in the first place.

Keeping them out altogether can be as simple as using a compost bin with a tight-fitting lid and making sure your compost is hot enough by adding plenty of carbon-rich brown material such as dry leaves, torn-up strips of paper and cardboard.

All of this will keep your compost free of larvae, help to break it down faster and even encourage a few earthworms to take up residence which is far more beneficial. 

Or, you could invest in a worm bin and add some different types of worms to produce nutrient-rich compost and worm castings. Plus, you’ll have the added benefit of worm tea that you can use to fertilize your pot plants.

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