Mar 03 2022

Exuviae and Frass for a Circular Farming System

What are exuviae and frass? These are terms I just learned and are probably new to you as well, but they may become more familiar in the future. Exuviae are molted exoskeletons from insects and are primarily made of chitin. Frass is undigested food from insects, so basically bug poop. Frass could make a good fertilizer for plants because it is high in nitrogen. Exuviae would not serve as fertilizer, but there are species of soil bacteria that can break down chitin for food. Adding exuviae to soil increases the population of these soil bacteria, which are beneficial to plants and make them more resilient to pests.

Exuviae and frass, therefore, can be extremely useful for farming. But where are we going to get the massive quantities of these materials that would be necessary to have any significant impact on our agricultural system? Well, we could farm insects for food and use the waste products of insect farming for plant agriculture. This could be the basis for a circular agricultural system. Organic matter from plant and animal farming can be used to feed insects which are also grown for food. The exuviae and frass from the insect farming can then be fed back into plant farming as fertilizer. This would not be a totally closed system, of course. Humans would be removing calories and nitrogen from the system to feed themselves, and human waste is typically not recycled as fertilizer (this is a separate issue – the risks and benefits of using humanure).

Insects are increasingly recognized as an important source of food. They have several advantages, the biggest being that they are small. This translates into a high food output to land use ratio. Raising insects also uses far less water than other food sources. Insects can also be easily farmed indoors, meaning they can be farmed year-round and in urban settings. Already there is significant farming of crickets, grasshoppers, mealworms, waxworms, and other insects for food. The insects are not generally consumed whole (although they can be), they are ground up and used as protein powder (such as cricket flour).

Raising high quality insects for food, however, requires that the insects be fed a high quality diet that includes protein, vitamins, and other nutrients. An agricultural system capable of feeding billions of humans needs to consider where all the nutrients are ultimately coming from. It doesn’t help much if we are feeding animals food we could be eating directly ourselves. But animals can be a way to convert non-human food into human food.

For traditional animal farming, this comes in basically two forms. Animals can forage on plants that are inedible to humans, such as grasses. They can also be fed food waste, or low quality food that is not suitable for human consumption. These calories are then converted into very high quality calories for human consumption. Of course, farmed animals are also fed high quality feed (usually as a finisher to pack on pounds), and this does divert farmland from direct human food production. But again, we have to consider the entire system. It still provides a path for turning non-human calories into human food. Also, animal manure provides about half the fertilizer for farmland, so this is also an important path for getting nitrogen into the soil. I am not saying the current system is optimal, but we have to look at the whole system if we are going to do a meaningful analysis and think about what changes would be useful.

How would insects fit into this system? Insects also can get calories from foraging. We have been doing this for thousands of years – bees provide food in the form of honey and they generally are allowed to forage for their food, converting flower nectar into food we can eat. Likewise insects for food can be allowed to forage. But if we are going to have an enclosed insect farming system foraging is not an option. In this case insects are fed organic waste, and they can be an efficient method of converting non-edible organic matter into food. The goal is to efficiently recapture as much of the nutrients in the system as possible.

But even with an optimal circular agricultural system, we will need to feed nutrients into the system, because humans extract nutrients from it. Again, foraging is one way to do this by capturing nutrients from the broader environment. The entire ecosystem of the planet is already a circular enclosed system. The nutrients we consume are ultimately returned to the environment. The energy we consume is replaced by a steady supply of solar energy. So ultimately what we are trying to do is balance our agricultural subsystem with the rest of the environment. Using waste as food just keeps nutrients in the agricultural system. Foraging takes nutrients from the broader environment and puts them into the agricultural system. But we also depend on synthetic fertilizer, which directly takes nitrogen from the atmosphere and turns it into fertilizer that is put into the agricultural system.

Whatever agricultural system we imagine in the future has to balance nutrient inputs and outputs. Farming insects can be a useful way to help do that, and it increasingly seems that insects will be an important part of the system in the future.

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