Mealworms or Black Soldier Fly Larvae In Compost: Here’s What You Need To Know

If you’ve recently spotted any maggot-like creatures in your compost, you may be wondering if they pose any risk to your pile.

Whether you need help identifying the larvae, or are certain about the species, this article will help you decide your next plan of action.

In this article, I cover:

  • How to identify what larvae are in your compost
  • If mealworms are beneficial for your compost (and when to get rid of them)
  • Why Black solder fly larvae are beneficial for your compost
  • Exactly how to get rid of mealworms and Black soldier fly larvae (if you need to)

Ready? Let’s jump right in.

Are mealworms good or bad for compost?

Mealworms are the larvae of the darkling beetle. They’re known for feeding on stored grains and cereals but will eat pretty much anything, living or dead.

Check out the video below for a time-lapse of mealworms eating different foods.

Finding mealworms in your compost is no reason to panic. They’ll be happily eating your organic waste and turning it into a nutritious soil amendment, just like normal worms. However, eventually, they’ll turn into a darkling beetle. These beetles aren’t harmful but can become a nuisance if there are too many of them. 

The beetles prefer to eat decaying matter, but they can damage live plants by chewing seedlings and feeding off leaves.

It’s also not very nice to have to deal with loads of beetles crawling through your compost when you’re trying to harvest it!

If there are only a few mealworms I wouldn’t worry about it and would leave them be. But if your bin starts becoming infested, I would try and reduce the population. I go through how to get rid of mealworms in compost in the next section.

It’s worth noting that mealworms are actually quite rare in compost. 

Black soldier fly larvae are much more common and are often mistaken for mealworms, so check you haven’t misidentified your mealworms before you take any action.

How to get rid of mealworms in compost

Spread your mealworm infested compost out on a tarp and let the birds eat the mealworms (source: sacratomato_hr)

Birds LOVE mealworms. The best way to get rid of them is to take the infested compost and spread it out on the ground or on a plastic sheet. 

Leave the compost there for a day or so. When you go back to it, all the mealworms should have been eaten by birds and other creatures. 

Try to pick a day when you’re sure it won’t rain to do this, otherwise you’ll have some very soggy compost. 

The bird trick will work with most larvae you find in compost. Birds love maggots and black solider fly larvae too. 

Chickens will pick mealworms out of the compost for you (source: jennalex)

If you have chickens you can also let them pick away at your compost. Mealworms make a tasty and nutritious snack for chickens.

Another option is to get your compost cooking!

Lots of creepy crawlies in your compost is a sign that it’s cold. This isn’t a major problem because cold composting works. 

But hot composting is a lot faster and most critters don’t like the high temperatures, so will leave the compost heap as it starts to get too hot.

Heating up compost is a whole topic of its own. Check out my in-depth guide on heating up your compost for more information on how to get started.

Mealworms and styrofoam in compost

This might surprise you, but mealworms can actually digest styrofoam. Scientists believe this is possible due to certain microbes in their guts that can biodegrade polystyrene. 

A study at Stanford University showed that 100 worms converted around half of the styrofoam into carbon dioxide (as they do with other foods) and then excreted the rest of the material as degraded fragments that look similar to animal droppings. The waste appeared to be safe to use on crops.

If you’re finding this hard to believe, here’s a video of some mealworms eating Styrofoam.

This amazing discovery needs more research, but it looks super promising because polystyrene was originally thought of as non-biodegradable. 

There isn’t enough concrete evidence to say anything definitive about the safety of the castings, but if you have some mealworms and some styrofoam that you’re looking to get rid of, you have nothing to lose by feeding it to the mealworms!

Mealworms VS Black soldier fly larvae

Mealworm (left) vs black soldier fly larvae (right)

Black soldier fly larvae can look very much like mealworms, with a few slight differences.

  • Black soldier fly larvae are slightly darker in color than mealworms
  • Black soldier fly larvae are shorter and fatter than mealworms  

Black soldier fly larvae darken with age, so will only look similar to mealworms in the beginning stages of their life.

In terms of compost, it’s much more likely that you’ll find black soldier fly larvae in there because their favorite food is decaying kitchen waste, whereas a mealworm’s favorite food is grains.

Black soldier fly larvae in compost: good or bad?

Black soldier fly larvae thrive in compost that’s moist, warm, and full of green waste.

Black soldier fly larvae are actually very beneficial to your pile.

The larvae will chomp through your green kitchen waste like there’s no tomorrow and help speed up its decomposition.

They’re ridiculously fast composters.

In fact, they’re so great for composting that people breed them and purposefully use them to reduce their waste. You can use them to recycle foods like meat and dairy that you wouldn’t normally put in a compost bin.

Here’s a video of black soldier fly larvae destroying a fish in record time:

One downside of having black soldier fly larvae in your compost is that they reduce the volume of the waste significantly. So much of the food they eat gets used by them, they poop hardly any of it out!

If your main aim is to get rid of your waste – this is fine. But if you want to have a decent amount of compost left for your garden, it’s not ideal to have a large population of the larvae.

Also, if you’re vermicomposting, the Black soldier fly larvae can crowd out the worms because they’re so active. You should try to remove them if you see lots of them in your worm bin.

The black soldier fly itself doesn’t have a mouth or a stinger so can’t cause any harm or damage (they can’t even eat!). Their sole purpose in life is to lay more eggs. Because they can’t eat, they die within a few days of emerging.

How to get rid of black soldier fly larvae in compost

If you decide you don’t want black soldier fly larvae in your compost, the easiest way to get rid of them is to mix some more browns into your compost. This will help dry the pile out, and the black soldier fly larvae will leave in search of somewhere more moist. 

Brown materials are things like dried leaves, cardboard or wood chips.

To discourage the females from laying eggs in your compost, you can put a thick layer of dry browns on top.