Meet the Professionals The Veg Plot

What is frass? The organic fertiliser made by flies…

Black Soldier Fly Frass

A few weeks ago we were introduced to an Irish company called HexaFly. As the name implies, they deal in flies and, in particular, the black soldier fly. They thought we might be interested in one their products, HexaFrass, an organic fertiliser produced by their flies’ larvae.

We have a bag and will soon be putting it to use on the garden, but first we wanted to find out more about the product and process behind making it. So we sent over a few question’s to HexaFly’s CSO Laura Healy for some fast frass facts…

What is a Black Soldier Fly?
The Black Soldier Fly, or Hermetia illucens, is a tropical insect known for its bioconversion abilities during its larval phase. These larvae can convert any organic material and have powerful enzymes and antimicrobial activity to help them excel in such conditions. They will happily digest waste material into frass fertiliser and work alongside colonies of bacteria and other microbes. They do not get sick, the relationship is symbiotic between the microbes and the larvae, and they do not host diseases. This makes them a much desired species to work with for bioconversion. 

How many flies do you farm? 
At any one time, we house millions upon millions individual Black Soldier Fly at different stages of their life cycle (eggs, hatchlings, larvae, pupae and adult flies).

How do you go about breeding and looking after these flies?
We have developed technology to successfully breed, grow and look after these tropical insects right here in Ireland. We carefully cater for their nutritional needs, environmental conditions and social behaviour. The Black Soldier Fly are very social amongst their colonies so it is important we ensure they can easily interact with each other and, in turn, promote natural breeding and feeding habits. 

One of the products you sell from these flies is the fertiliser ‘frass’. What is frass?
Frass is essentially the poop of any insect, in this case the Black Soldier Fly Larvae. As they feed they produce a fine waste material called Frass. It is an excellent, powerful natural fertiliser. Our HexaFrass is certified-organic. 

What are the benefits of using frass on the garden?
Studies have shown its ability to deter pests such as aphids and so is a brilliant natural way to fend off unwanted pests! It also contains chitin which is a biopolymer known for eliciting an immune response and promoting growth of healthy soil microbes. It has an NPK* of 3-1-1.

What other products do you sell from Black Soldier Fly farming?
We have a range of products for multiple industries such as the pet food industry, plant nutrition industry, poultry, hen and animal feed industry, feed ingredients, human care and cosmetic and oleochemical industries.

Our HexaMeal is a protein-rich meal made from the Black Soldier Fly Larvae. It is a replacement for unsustainable fish meal and soy-based meals. It is also sought after to make pet food like healthy dog treats. 

Our grubs are a fantastic feed for hens and chickens, with research showing a better tasting egg arising from hens fed Black Soldier Fly Larvae! It makes a lot of sense – insects are naturally part of free-roaming hens and other poultry so these results aren’t all that surprising. Studies have also shown grubs to be a valuable environment-enricher for hens and poultry. 

Are you looking at farming other insects in future?
Right now we have so many avenues to explore with the Black Soldier Fly. However, as the insect revolution progresses and we get more used to the idea of not only feeding insects to our animals but as a food for humans too, who knows what other opportunities will arise in this upcoming sector. 

Can humans eat Black Soldier Flies? If so, what do they taste like and what drink would you recommend pairing with them?
Yes, some companies are producing products for humans with Black Soldier Flies. We heard they are delicious when roasted, not far off bacon – so in that case we would suggest a crisp apple cider to go with a plate of oven-roasted Black Soldier Fly Larvae!

Black Soldier Fly fertiliser

For more information on HexaFrass, visit the HexaFly website at

*Nitrogen (N), Phosphorous (P), Potassium (K)

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