Food waste and flies: A win-win?

Feeding food waste to Black Soldier Flies to turn into high-protein animal feed can help replace 20 per cent of our soy imports. Emilie Filou reports.

Delivery day is a busy day at AgriGrub: 10-20 tonnes of rotting fruit and vegetables are dumped in the company’s courtyard, it’s then a race to feed it all through the shredder and load it into large storage tanks where a probiotic is added to stabilise it. Just 24 hours later, it is ready to use: this will be feed for AgriGrub’s voracious residents, Black Soldier Fly (BSF) larvae.

The Cambridgeshire-based company has been farming BSF since 2018. Insects such as BSF are tremendous sources of protein, which can be used as an alternative to environmentally harmful proteins such as soy and fishmeal. BSF larvae can be fed live to some livestock; they can also be processed into insect meal for use in aquafeed or pet food.

The idea that insects can convert organic residues found in food waste into new protein is one of the most compelling arguments in favour of insect protein. A recent report by WWF and Tesco found that using insect protein in animal feed could replace 20 per cent of the UK’s soy imports by 2050.

The report, which sets out a roadmap for the UK to accelerate the adoption of insect protein in animal feed, also found that just under half of the demand for insect protein could be produced by British insect farms. In the process, they would upcycle 3.4 million tonnes of feedstock ingredients (ingredients that can be used as insect feed) into high-value protein.

This is exactly what AgriGrub is doing: the rotting fruit and veg the company receives is mostly food that was damaged in transit from Europe and that would otherwise end up in landfill. Joe Halstead, managing director of AgriGrub, says that their focus is actually on waste management rather than protein production per se, a decision motivated by their desire to tackle emissions connected to food waste and landfill.

Joe Halstead
Joe Halstead and AgriGrub measure their output in the amount of waste processed. Image Emilie Filou.

“For us producing protein is a happy by-product. But it is essential to be closing the loop: being able to use grubs to feed animals, rather than turning them into some sort of disposable product, inherently has more value,” he explains.

Tellingly, AgriGrub measure their output in waste processed rather than protein produced (the industry standard). Their ambition is to convert as much as possible of the UK’s 9.5 million tonnes of food waste through insects: they are gearing to open a new facility in Tydd St Giles later this year that will process 10 tonnes of waste per day, up from 500kg at their current Soham site.

The difficulty is that the “waste” insect companies are allowed to use is severely limited: insects are considered farmed animals, which means that they cannot be fed anything containing meat or fish, or prohibited materials such as household waste, animal manure, human waste etc. The rules go back to the BSE crisis, but many now acknowledge that restrictions aimed at conventional livestock aren’t appropriate for invertebrates, especially insects like BSF that are saprophagous (feed on decaying matter).

“This is a whole new species of farmed animals, and that comes with opportunities to move things forward,” says Dr William Clark, a bioeconomy specialist at Zero Waste Scotland and chair of Insect Industries UK, which represents stakeholders with an interest in the use of insects as feed. “We recognise the bioremediation potential of insects: they evolved 66 million years ago, we can use them to add value to things like farmyard manure.”

Fruit and veg waste
Black Soldier Flies can convert food waste into protein. Image Electric Robin. 

One of the key recommendations of the WWF-Tesco report is to broaden the range of allowed feedstocks to farm insects. Mollie Gupta, WWF forest commodities manager, says it is essential for several reasons. The first is that many of the current feedstocks used for insects, such as spent brewers’ grain, can be fed directly to livestock; it therefore makes no sense to feed these to insects. The second is that as insect farming scales up, it will need more feed sources and will come into competition with other waste diversion strategies such as anaerobic digestion, which is subsidised.

The report identified six potential new substrates, three of which are included in the “achievable” scenario of the roadmap (such as food surplus from manufacturing). The other three, which include food-based anaerobic digestate and chicken manure from laying hens, will require more mettle from the regulator.

For Halstead, it’s about striking the right balance between safety and circularity. “I think there is a place for meat and fish: as a substrate, it’s amazing. You won’t get bigger, faster-growing BSF larvae on anything but a nice 50:50 blend of fruit and veg and meat or fish waste. They love it,” he says.

Joe Halstead
Deciding what waste can and should be fed to insects is a source of debate. Image Emilie Filou. 

Clark says it’s important to look at it from both sides. “Insect protein is a very new ingredient for aquafeed manufacturers. It’s a very optimised industry so small changes could have a massive impact downstream,” he says. “We’re still searching for a crossover between what’s an ideal salmon diet and what’s an ideal insect diet.”

A study from the University of Stirling found that consumers are happy with the idea of including insects in aquaculture feed, but they’d rather the insects ate vegetables. The study indicated however that people knew very little about animal feed and that education may therefore increase people’s acceptance of insect-based feed – perhaps even if the insects did eat meat and fish.

“We need to think about the language,” says Clark. “If you said: ‘this is an organically-fed, insect-reared salmon’, we move the conversation forward.”


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  1. I love this idea! Have been campaigning for Tesco to stop destroying the rainforests to grow soya for animal feed. Greenpeace have been sending out packs for supporters to target Tesco which is the biggest UK seller of rainforest detroying animal feed and meat. Congratulations AGRIGrub!
    I see Tesco is trying to improve their reputation but it might be spin ???


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