Silkworms Part 2: Caterpillars in general

Here is our rather delayed (apologies!) discussion of caterpillars in general as a food source, following our experiments raising silkworms, and informed by some small scale experience raising Sphinx Moth caterpillars (Tobacco/Tomato Hornworms). As we proclaimed in our earlier post “we believe caterpillars are an extremely promising food source”. Let’s go over why.

Caterpillars are the larval forms of moths or butterflies. They emerge from their eggs with the sole mission of finding food and eating it (while staying well enough hidden to avoid predators) until they are large enough and have enough stored energy to pupate – temporarily becoming a sack of free floating proteins and genetic material that reorganizes itself into the adult moth. As such, the caterpillar is behaviorally a perfect livestock candidate. It is not concerned with physical exercise – there is neither physical nor moral imperative for “free-range” caterpillars. There is also no issue of force-feeding – given the opportunity in nature, a caterpillar will eat, more or less constantly, through this entire phase of its life.

In addition to their favorable behavioral tendencies, caterpillars are also physically well suited for human consumption. Unlike the larvae of many other insects (e.g. mealworms), caterpillars do not have an indigestible exoskeleton which means better texture and you get more nutritional bang for your buck, and they are extremely high in protein (Hornworms measuring in ~60% protein by dry weight based on nutritional testing done for http://www.greatlakeshornworm.com/). These attributes make them great for ground-meat applications such as burgers. They also tend to grow VERY fast. In one experiment, our hornworms grew from 1 inch length to 4 inches length in just two weeks, and silkworms can take just 28 days from hatching to pupating. Plus, as you can see in the last sentence, they get BIG. Big is good for a lot of reasons – you can raise fewer of them, and they are easier to contain as they quickly grow too big to squeeze through standard screening.

So this all sounds great! It should be a piece of cake to start rearing thousands of caterpillars in our closets and cupboards and quickly wean off our dependency on traditional animal livestock. But, as always, there’s no free lunch and the better product comes at a higher price. That higher price for caterpillars comes in the form of labor and energy required for careful habitat management required to successfully raise large populations of caterpillars, which is much greater than required for other popular species like crickets or mealworms.

Firstly there is the issue of waste. Caterpillars eat a lot, and eat fast. This also means they produce a much higher volume of waste and at a much higher rate than their smaller counterparts. The waste is moist and high in ammonia so it must be cleaned out frequently to avoid mold growth and prevent the evaporating ammonia and other gases from poisoning the caterpillars. As a result these critters should not simply be grown in a flat tray on a substrate of food (which is space efficient and works well for “dry” species like mealworms), because it can be very labor intensive to separate out the caterpillars to clean their habitat. Their soft bodies must be handled very carefully to avoid bruising, so mechanical separation methods like the one we developed for mealworms are not usable. Instead the caterpillars should be raised vertically, such as on a mesh, below their food source so they orient to eat from the bottom of their food, and let their droppings fall onto an easily removable and cleanable surface or container. This setup is common in small scale “worm cups” sold to grow and keep hornworms for pet food, but may be trickier to design for a larger scale. (Note this problem is most prevalent when feeding caterpillars an artificial diet. Silkworms are traditionally grown in flat trays filled with mulberry leaves and will migrate up through a net to a clean layer of leaves. However as discussed previously, the dependence on fresh mulberry leaves renders silkworm rearing uneconomical in North America, and it may not be desirable or possible to raise other caterpillars on fresh leaves).

The other main concern with raising caterpillars is their environmental requirements. They generally need high and consistent temperature and humidity levels in order to stay healthy and grow quickly. This requires more active climate control both to maintain these levels, and to ensure good ventilation and fresh airflow to inhibit the growth of molds and fungi that also thrive in warm humid environments. While it is reasonably simple to maintain temperature and humidity with a simple thermostat, fan, and moisture source, it still requires extra attention and electricity. The habitats will require more careful design and maintenance – possibly even utilizing custom components, versus inexpensively assembled off-the-shelf setups that work so well for species like mealworms

In spite of the extra work and planning involved, the up-sides of raising caterpillars for food are significant, and we are continuing to investigate species and rearing methods, and we wholeheartedly encourage others to do the same. Keep an eye on this space as we will be sharing designs and advice for growing and harvesting many species of insects.



Andrew Brentano
Co-Founder, Tiny Farms