Munching maggots

(From "Horizons" no. 110 September 2016)​​​

The black soldier fly is a veritable
eating machine – at least in its larval
stage. Despite its rather martial
name, it's not an insect that would
ever do anyone any harm. Its larvae feed
on rotting organic material such as food
scraps or dung. "They can reduce most of
just about any type of organic waste in a
short space of time", says Noah Adamtey
from the Research Institute of Organic
Agriculture
(FiBL) in Frick.

Adamtey is running the scientific section
of a project that aims to employ the appetite
of soldier fly larvae (Hermetia
illucens)
in developing countries. It is being implemented
in the greater metropolitan area
of Accra, the capital city of Ghana. "Just as
in other big cities in tropical regions, composting
is poor in Accra", says Adamtey.
On the one hand this leads to immense
hygiene problems because organic waste
makes up more than half of the total refuse
in developing countries. On the other
hand, it's also a waste of natural resources
– because while the rapidly increasing
population is dependent on productive
agriculture, the soil is exhausted
and not
very fertile.

Feed for fish, chickens and songbirds

This is why, in collaboration with Ghanaian
colleagues in Accra, researchers at FiBL
want to make composting worthwhile for
the local population. To do this, organic
waste is fed to tiny soldier fly maggots.
Because they chew up the waste in record
time, says Adamtey, composting time is
reduced by roughly a third to less than
80 days. Farmers can then use the valuable
compost in their fields. An additional goal
of the project is to provide a further use for
the maggots of the soldier fly – as feed for
fish farmers, who find it difficult to meet
the Ghanaian population's appetite for
fish. "The larvae are an extremely interesting
source of animal feed when you consider
their protein and fat content, plus
their amino acid profile", says Adamtey.

Stefan Diener agrees – he's studying
the waste recycling properties of the black
soldier fly at the Swiss Federal Institute of
Aquatic Science and Technology (Eawag) in
Dübendorf. For example, he sees potential
in selling dried larvae to chicken breeders
in Uganda, who traditionally mix their feed
themselves. An Eawag project in Indonesia
is also planned that will sell the living larvae
to local songbird owners.

The most important aspect of such projects
is to provide value to organic waste in
developing countries, says Diener. "If the
waste can't be used profitably, then huge
mountains of garbage lie around and turn
into a massive, stinking problem". But it
depends on local conditions whether or not the soldier fly is the best solution. "If
the energy demand in a region is very high,
biogas
could be more profitable, for example". The organic waste would then be
turned primarily into methane.

When larvae chew on scrap metal

You also have to make precise checks as to
what the pitfalls might be in individual
cases, says Diener. Because soldier fly composting
means you have to produce fly eggs
continually on the spot and have a rational
separation process to separate the mature
maggots from the compost. "And you have
to be certain that the customers buying the
larvae will accept animal feed that's been
produced from waste". If these conditions
can be met, then the soldier fly has great
potential.

This is the case in Accra, where Adamtey
says the FiBL project is on track. The basic
biological checks have meanwhile been
completed, he says, and guidelines for the
local population are being drawn up to inform
them how to make compost with soldier
flies. One problem remains, however;
in Ghana, organic waste is often not separated
from inorganic waste. This makes
composting more difficult. Because when
they eat plastic, glass or electronics, the
larvae of the black soldier flies ruin their
mouths.

Simon Koechlin is a science journalist and chief
editor of Tierwelt.