Meal Worms in Compost – Good or Bad? (Could it Be Black Soldier Fly Larvae?)

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When you first begin composting, as you begin to research, you will come across lots of tips and tricks to speed up the process of breaking down organic matter.

One of these may have been the idea of introducing mealworms in your compost bin so they can get to work on breaking down some of the material for you as they eat decaying matter.

  • But are mealworms in your compost a good or bad thing?
  • Do the benefits outweigh the negatives when it comes to having these darkling beetle larvae in your composting material?
  • Are they even mealworms!?

Read below to learn everything you need to know about how mealworms affect the composting process.

Larvae in Compost Bin: Mealworms Vs Black Soldier Fly Larvae?

Although they may look similar and have similar eating patterns, mealworms and black soldier fly larvae are actually distinct and different creatures to have in your compost.

So if you think you may already have mealworms in your compost bin, you will first of all need to work out exactly what you are dealing with.

Let’s look at the differences:

What are Black Soldier fly larvae?

Black soldier fly larvae are grub-like younger versions of the black soldier fly, which are generally considered to be quite benign presences in a garden.

When at the larvae stage, these creatures have a huge appetite and will consume up to twice their body weight daily.

They will use the energy derived from this food to grow quickly and leave very little waste in their wake.

Black soldier fly larvae are originally pale beige in color with dark rings around their bodies but will become a darker grayish brown as they mature.

How do Black soldier fly larvae differ from meal worms?

Mealworms, in contrast, are the larvae stage of darkling beetles.

While in the larval stage meal worms will also consume and eat a large amount of material in your compost pile including decomposing vegetables, plant matter, and dead insects.

Meal worms are distinguishable from BSF larvae by their color and shape.

These worms will be a lighter, brown-yellow color and be thinner and longer when compared to black soldiers in the larval stage.

They look like small thin caterpillars and can grow up to 3cm long.

Meal Worms in Compost Heap

So are mealworms good for compost piles?

Below we will take a look at the pros and cons of having these creatures available for consuming dead organic matter.


  • Mealworms feed on the decaying organic matter in your compost pile and the mealworm manure created called frass can be used as fertilizer to support plant growth in your garden.
  • Mealworm populations in a compost heap will consume food scraps as a natural preference, but they don’t eat only food and will consume a variety of other matter that you place in the pile. There have also been instances of mealworms eating styrofoam.
  • Making the decision to raise mealworms for your compost means you will also have a ready food source if you have chickens, lizards, or other creatures which enjoy eating them.
  • Meal worm populations will grow pretty quickly so you don’t have to buy many more mealworms to get a good number at work in your compost.

FUN FACT: a female darkling beetle will lay eggs 70-100 at a time!


  • The waste that mealworms produce is not as good for fertilizing as that created by red wigglers or other composting worms.
  • In order to keep the population thriving, you may need to supplement their diet with grain and wheat bran.
  • They are not suited to the hot composting process and won’t do well if the compost heap gets too wet.
  • Once they are adult beetles, they will be of little use.
  • Mealworms may attract vermin and other insects or critters looking to make them their next meal!

Black Soldier Fly Larvae in Compost Heap


  • These hungry creatures will consume all kinds of matter, plants, and kitchen waste that you put in your pile.
  • Because they consume so much each day (up to twice their body weight) if you have a good size population in your compost, the process of turning to waste into fertilizer will be quickened.
  • They are such unfussy eaters that you can use them to consume and recycle meat, fish, and dairy!


  • Using black larvae in an above-ground compost pile could contribute to a worsening smell.
  • Once black soldier fly larvae have found a home in your garden they will be difficult to eradicate.
  • Because they are such heavy eaters, you may find that the size of your compost pile reduces quite quickly.
  • If you are vermicomposting, it is worth noting that you might find the larvae beginning to crowd out your red worms/red wrigglers or nightcrawler earthworms.

Will Mealworms Help My Compost Bin?

Mealworms will help to speed up the process of creating fertilizer in your compost by consuming dried leaves, food scraps, and even styrofoam.

They will create waste in their wake which can be used as a fertilizer and are generally considered a positive presence in the composting process.

Meal Worms in Compost blog post image

Is Mealworm Poop Good for Plants?

The manure of mealworms is called frass and can work as a great fertilizer in potting soil to support the growth of healthy plants and flowers in your garden.

Are Darkling Beetles Good or Bad For My Compost Pile?

Meal worms won’t remain in the larvae stage forever and once they reach adulthood will be darkling beetles.

And if these beetles move to other parts of your garden you will find that they consume the seedlings and young plant growth that they come across.

So this is something you need to consider if you have a vegetable patch near your composting.


In conclusion, mealworms have plenty of things to recommend them to your composting method.

While in the larvae stage, meal worms can be a great presence in your compost and will help to break down the matter you place in your heap, from food scraps to styrofoam!

As they consume matter they will be leaving behind their manure which serves as a great fertilizer for plants.

However, these worms can be fussy in terms of the temperature and dampness level in which they will thrive and you may also need to add grain at certain points to supplement their diet.

You will also need to consider what will happen once they become darkling beetles and whether this is a presence you want to deal with in your garden.