Mealworms can be both good and bad for compost, depending on your situation. In short though, they won’t do any harm and are not dangerous.
In regards to being good for compost, the mealworms will help break down the natural materials by consuming them. This is good because that is what composting is all about; decomposition.
However, mealworms do not remain as ‘worms’ (larvae) forever. They eventually transform into beetles, often called Darkling Beetles. The beetles eat pretty much any vegetation so they could become a problem in your vegetable garden.
Additionally, if you have been aiming to create a hot compost to aid in quick decomposition, the presence of mealworms might indicate that the heap is too cool. In a hot compost, mealworms won’t survive.
Below some additional details are covered when it comes to mealworms and a healthy compost, considering the vital question: Are mealworms good or bad for compost?
What Are Mealworms
Mealworms, when at the larvae stage, are short worm-like critters with a scaly-looking, hardened outer. Their outer layer gets harder as they mature.
They are a yellow color with darker coloration at the body segments. They have small legs, near the front of their body.
The larvae stage of a Mealworm Beetle is probably what you have found in your compost. However, from this worm-like creature they eventually (after the Pupae stage) turn into Mealworm Beetles or otherwise known as Darkling Beetles.
These beetles are very dark, black, or brown and have a hard outer. They begin light when they first transform into a beetle and then darken right through to a black color.
They look like a typical beetle and very different from the larvae they began from. It’s at this stage that they reproduce and lay eggs, ready for the next cycle of mealworms to begin.
They eat decaying, or fresh, vegetation so, an infestation of Darkling Beetles after having mealworms in your compost could mean you have more bugs eating your vegetable garden.
Interestingly, the beetles may also eat mealworm eggs or larvae.
Mealworms are popular as bird, reptile or fish food. Some people will breed them for this reason and sell batches of mealworms for pet food.
The container of mealworm larvae intended for pet food is normally refrigerated to keep their growth cycle dormant, aiming to keep them at the larvae stage for longer.
Environment Needed For Mealworms
Mealworms are very heat sensitive and usually prefer temperatures around 70°F (21°C).
If your compost is a smaller, short pile or fairly new – it could be in this lower temperature range and perfect for mealworm habitation. The heat of the compost may also depend on the composition.
Mealworms will eat grains if available, but also vegetation. So, in your compost, they will likely have plenty to eat if you have food scraps in there.
Additionally, they do require some moisture that they could get in the compost from scraps like, for example, banana peel, potato, carrot, or apples.
Ideal Conditions for Compost
Warmer conditions in the compost pile speed up the process of decomposition. Some compost gets hot enough that there is visible heat radiation.
So, a warm compost will break down the matter it contains faster. A hot compost can also create conditions unsuitable for mealworms, so you then don’t have to worry about them.
A compost that is fairly low or moderate temperature can still be a good, productive compost. Plus, different bugs and critters in a more habitable compost will eat different plant matter and contribute to the overall decomposition too.
So, either condition has its benefits. If you have mealworms thriving in your compost, then it is probably not very hot.
Benefits Of Mealworms In Compost
Critters in your compost means that they will help break down the natural materials. This is exactly what you want in a compost heap. So, in this regard, mealworms are welcome.
If you were interested in using mealworms as pet food, you might have accidentally started breeding them in the compost. Alternatively, if the compost is ready to spread when the mealworms are present, local birds will be very grateful for the easy pickings.
Additionally, as the mealworms digest the materials in your compost and leave it behind as droppings, it turns it into nutrition for your soil. Again, this is, like with many bugs, helpful to a compost heap.
Downsides To Mealworms In Compost
The larvae feed on grains mostly but will go for any plant growth too, if that’s all that is available.
So, in the garden they can eat up your latest seedlings. In the compost you might be happy about it, however, anywhere else in the garden can be a pain.
Another drawback to mealworms is that they do not remain as worms, not like earthworms do and so on. So, from a larva (worm-like) they become a pupa.
This is another transition stage before becoming a beetle when they appear caterpillar-like and do little more than wriggle around. At this stage, they are harmless to your compost.
Then, they become beetles. These beetles may then lay eggs and the cycle begins again. If the mealworm larvae do mature to become beetles then you could end up with many critters crawling all over your garden and compost.
They may also nibble on your vegetable garden.
The beetle will eventually die, some only live for a few months. Then, you will have many deceased beetles throughout your compost that can smell as they decompose.
The critters will also be leaving droppings in your compost that could smell too.
Mealworms aren’t terrible additions to the compost heap, but you need to be aware they may all turn into Darkling Beetles. Extra beetles in your garden mean more pests eating your plants.
Mealworms in compost might also mean that your compost isn’t hot. A hotter compost will lead to faster decomposition and the temperature will make it inhabitable for mealworms.