Over the warmer months it is not uncommon, when turning our compost piles, to uncover a particular fly’s larvae (or maggots) in our compost. They are long, segmented grub-like creatures, ranging in colour (white – dark brown) and length (5mm – 20mm), depending on where they are at in their life cycle when we discover them.
What are they doing there, and should we be worried?
The simple answer is no. They are black soldier fly larvae and when it comes to compost they are friend, not foe.
Black soldier fly larvae feast on organic material such as food scraps and decomposing plant matter. They like warm temperatures (28-32 degrees Celsius) and a nicely damp (50-80 per cent humidity), dark environment, so during the warmer months our compost piles are the perfect nursery for these little friends.
Not only do they help out with the breaking down of the organic matter in our compost, if you have chooks they have the added benefit of being a great addition to their diet as they are high in calcium so help with healthy egg shell production.
The life cycle of a soldier fly is approximately 38 days. Firstly eggs are laid. We can encourage adult soldier flies to lay eggs on our compost pile by placing a piece of corrugated cardboard on top, as they don’t lay their eggs on their food source but just above.
These eggs hatch, drop down into the compost and spend the next two to three weeks as larvae eating and growing in our compost pile. As they mature they get bigger and darker in colour until they are ready to pupate and emerge as adult flies.
While the adult flies look a bit scary, like a wasp, their bark is certainly worse than their bite. In fact, they have no bite.
During the adult stage of their life cycle (about five to eight days) they actually don’t have mouth parts capable of biting or even eating. This means they are harmless to our living plants and vegetables, as well as us. Life as an adult soldier fly is all about mating and laying eggs, no time to eat.
In a healthy and happy compost pile, black soldier fly larvae will be the only maggots there. In a sluggy, stinky ‘dump and run’ nacho-like compost pile, it is possible to attract the common house fly maggots, which can spread disease by vomiting their way around the place.
Healthy compost piles attract the helpful soldier fly larvae, it’s a win-win situation.Yet another good reason to keep our compost pile sweet and happy.
– Mikaela Beckley works with *Yes In My Back Yard, (YIMBY), a community-scale composting initiative in Castlemaine and surrounds. Send questions or comments to hello@yimbycompost.com, or to book in for a compost workshop.
