6 Ways To Use Caterpillar Poop On The Garden (Science-Based)

The truly dedicated gardener knows that caterpillars eat and poop a lot. However, very few are aware about the different uses of caterpillar poop.

Caterpillar poop or frass can be used in at least seven ways: 1) for defense and protection, 2) nutrition, 3) communication, mating selection, and navigation, 4) as soil conditioner, 5) for stronger and healthier plants, 6) as bio-fertilizer, 7) as well as in scientific and medical research.

Since there are more than 20,000 kinds of caterpillars in the world and since they all poop all the time, you can imagine how much poop we’ve got. On the other hand, only a few know the different ways how all that poop can be used.

This article can tell you all about that. Ready?

1. For Protection

In the insect world, frass is not just waste matter. In fact, it can be used as bullets, deterrents, or shields against enemies and predators. Caterpillars are largely defenseless but have developed different ways of using what they’ve got on hand, such as frass.

  • Bullets: Some species can eject their waste like bullets at about 1.3 miles per second, as well as over long distances as a mechanism to keep natural predators away. Older caterpillars can shoot poop over longer distances, which is equivalent to 76 yards in a football field.
  • Deterrents: Research indicates that frass can drive away from natural enemies as well as serve as natural biocontrol agents against destructive pests.
  • Shields: Other insect species hide under their frass as a protective cover against prey. Studies indicate that frass can be used as an organic fungicide.
  • Others: Other protective uses include frass chains, fecal shields held up like umbrellas (see photo), and frass frocks (see photo).

FACTOID: The poop pellets excreted by insect larvae and the powdery material from insect borers are called “frass” from the German word Fraß (frasz), which refers to an unrefined or animal-like way of eating.

Watch this caterpillar poop - Real, uncut, funny and amazing

2. For Nutrition

Caterpillars are larva that develop into moths, butterflies, or other insects. They’re “eating machines” with stomachs good for buffet-type gorging. They don’t exercise but they don’t become obese. Instead, they poop a lot. All the time.

The thing is, frass can also be used to provide food as well as to absorb more nutrients. Humans also use frass as food in fish farming as well as for producing probiotics and antioxidants.

  • To trick plants: Caterpillar poop (frass, feces, or excreta) contains chemicals that disable the defense mechanisms of plants. This allows the caterpillars to eat as many leaves as they want, according to researchers at Penn State University.
  • To eat more: Caterpillars poop so that they can eat more. Did you know that caterpillars eat as much as 27,000 times their own weight and increase their body mass by more than 1,000 times? After squeezing out nutrition from all the food they eat, the rest is excreted as poop.
  • In fish farming: A 2020 research paper found that larval frass used as food for catfish can increase production up to three times. The research concluded that frass makes catfish diets more palatable as well as provides catfish with a sustainable protein source.
  • To cultivate food: Some species use frass to cultivate a fungi garden for snacking. Research indicates that frass can be a viable source of agro-food as well as of probiotic yeast and antioxidants.

FACTOID: If you don’t want to eat frass accidentally, don’t picnic in the forest, and keep your mouths closed when looking up.

3. For Communication

The various chemical and biological contents of insect frass contributes to its use in mating and in identifying friendly hosts, to keep away enemies and predators, and to control population growth.

  • To attract: In a 1997 paper, Japanese researchers found that the frass of some insect species contains pheromones that attract others of the same species through the sense of smell. Other species also use chemical-infused frass to attract mating partners as well as to find insect hosts.
  • To select: One parasite identifies the best host larvae and avoids dangerous hosts based on the chemical content of the larval frass, according to a 1995 paper published in the Journal of Insect Behavior.
  • To navigate: Other species use their frass to find their way home. Other research indicates that chemical cues in frass can be used by insects to identify hosts or their habitats, as well as to identify attack sites.
  • To protect: Most unusual, however, are insects that use larval poop as shields against enemies, as well as to protect eggs against attacks. Larval frass can also deter the Egyptian cotton leaf worm, the European corn borer, and the North American bark beetle. In other words, caterpillar poop is an eco-friendly pesticide!
  • To deter: Larval frass is also found to be an effective deterrent from oviposition. According to a 1992 paper on insect physiology, a blend of at least six chemicals in larval frass can stop adult females from laying more eggs.

FACTOID: Zoom in to a close-up of caterpillar poop, and you’ll see a surface similar to corn on the cob. According to naturalist Greg Greer, this is formed by the muscles of the caterpillar’s digestive tract.

4. It’s a Soil Conditioner

Frass from tiny caterpillars looks like dark green, brown, or black specks or strawberry seeds. Larger caterpillars produce frass that looks like very small seeds (see photo). While most are small, hard pellets, some bugs and insects also produce liquid frass.

  • Ready-to-use chitins: Unlike most garden fertilizers, caterpillar frass contains plant-digestible chitin that conditions the soil and makes plants stronger.
  • Soil inoculants: In addition, insect frass is a natural soil inoculant against the eggs, spores, and seeds of alien or invasive species that can contaminate the soil.
  • Soil amendments: Researchers confirm that frass is an effective agent of soil improvement and soil amendment. It can also:
    • improve the nitrogen content of soil,
    • reduce fertilizer use,
    • reduce negative effects on the environment,
    • make more nutrients available to plants, and
    • affect various soil processes.

PRO TIP: Wash your greens very carefully, or you’ll be eating caterpillar frass without knowing it.

5. It Makes Plants Stronger

The chitin in caterpillar frass makes plants stronger by helping plants resist nematodes and root rot, as well as trigger the autoimmune system of plants. Caterpillar frass is a major contributor of nutrients in forest floors.

  • Beneficial organisms: Frass is said to contain an abundance of beneficial microbes, bacteria, and fungi. A published analysis indicates that each gram of frass contains as much as 240 million CFUs (colony-forming units) of fungi and bacteria.
  • Increased productivity: Composted frass of insect larva has been found to increase vegetable growth by up to 30%, according to research from the University of Singapore.
  • Resistance to infections: Research confirms that frass contributes to plant stress resistance and growth, stronger plant tissues, as well as more robust gardens that are resistant to pests such as fungal gnats.

FACTOID: If you’re in the forest and hear the pitter-patter of rain but you remain dry, that’s not the sound of rain: that’s the sound of caterpillars pooping. If you can imagine, millions of them, in fact.

6. It’s a Gentle Bio-Fertilizer

According to a research study, frass contains rich nutrients that are readily available for plants to absorb. At the same time, frass also improves the microbial activity in soil.

  • Soil enrichment: A research paper indicates that frass gathered from insect farms can improve nitrate and dissolved nitrogen content in garden soil.
  • Growth stimulant: Many commercial providers of caterpillar frass claim that it can be used to stimulate plants to produce more fruits and vegetables. At the same time, frass also helps lawns produce greener, healthier grass.
  • Natural organics: Frass also contains bacteria that provide nutrition to plants in addition to nitrogen, potassium, and phosphorus (NPK) that plants need. At the same time, frass is a viable organic alternative to commercial fertilizers and soil amendment products.

Other research point out the benefits of using frass as organic fertilizer in small-scale farming to improve soil fertility as well as to improve crop yields.

Extra Use: For Science

Various cultures through the ages have been using caterpillar frass to increase the reach of human knowledge in various fields of study.

  • Entomology: Frass has been used by scientists to measure the population density of insects in forests, determine the effects of insecticides on insects, the larval population density, as well as to see how weather affects the intensity of feeding or food consumption.
  • Biological control: Other researchers use frass to investigate how microbes affect the development of larvae, to identify specific larvae, to control insect populations, as well as to determine the patterns of growth among insect populations over time.
  • Medical applications: Some species excrete frass that contains centrin, a protein that is involved in the cell division of cancerous growths. At least one type of frass can be used against a large number of bacteria.
  • Alternative treatments: The silkworm caterpillar excretes poop that can be used to treat inflammations, fevers, and relieve pain.
Insect Frass For The Garden - Off Grid Homestead

Where To Get Caterpillar Frass?

Now that you know the many wonderful uses of frass, you’re probably wanting to know where to get it.

  • Large-scale suppliers: The larval meal industry produces by-products such as larval poo and shedded exoskeleton, both of which are nutrient-rich bio-fertilizers. For instance, the Texas Butterfly Ranch cultivates caterpillars that provide a constant and plentiful supply of frass (photo).
  • Local sources: Because caterpillar frass is tiny and difficult to gather, your best bet is to buy frass from commercial breeders of mealworms, crickets, as well as from butterfly farms. Those who raise caterpillars remove frass every day for sanitation.
  • Product quality: Keep in mind that frass quality is highly dependent on what the caterpillars eat. For instance, if they eat leaves from fertilized plants, you’ll get more nutritious frass.

Sources: Here are some sources that can be your ready sources of larval frass:

  1. Pritchett’s website sells natural fertilizers of mealworm frass by the pound for seedlings, indoor as well as indoor plants.
  2. The Entera Frass website sells dried manure from black soldier fly larva that are fed fruit and vegetable scraps. The fertilizer can be stored for a year.
  3. The Entocycle website sells fertilizer made from insect exoskeletons, organic substrate, and frass of larvae.
  4. The Rocky Mountain Microranch website announced a 25% discount on their insect frass, sold as ready-to-use soil amendment.
  5. There’s organic insect frass sold in two-pound bags that you can order online.
  6. TeaLab can provide you with insect frass that can be used as fertilizer as well as to help your plants combat disease. It’s also sold online in 10-pound bags.
  7. Arbico Organics announced a 5% discount on your first online order of larva frass that you can use as soil amendment.
  8. You can order 1/2 pound bags of insect frass from the Buckeye Organics online store.
  9. AgriGrub is testing the UK market for its offerings of frass fertilizers. You can contact them online.

How To Apply Frass On Your Soil?

There are at least three ways to use frass in your garden: as a deep soil mix, when watering plants as foliar feed, or as a root drench.

  • Foliar feed: You can dissolve 5 grams (about 1 teaspoon) of frass in a gallon of water for watering the garden.
  • Root tea: Dissolve about half a cup of frass in a gallon of water (about 3.75 liters) and apply around the root perimeter of plants. You can also spray a mix of 1 teaspoon frass per gallon of water.
  • Deep soil mix: Commercial frass is dry and can be mixed into garden soil. Recommended application is one pound (almost half a kilogram) for every 20 square feet (or almost 7 square meters) of garden soil.
    • For lawns and garden beds: Mix deep into the soil about 1 pound (0.45 kg) of frass for every 20 square feet (about 7 square meters).
    • For trees, berries, and potted plants: Mix about 1 tablespoon of frass in about 3 cups of soil and mix around the roots.

Frequently-Asked Question

What’s the red stuff in caterpillar poop? The red fluid you see is meconium, the caterpillar parts that are left over after making the butterfly.

Does caterpillar poop smell like our poo? No because they don’t eat human food.

Can caterpillar frass be harmful to humans? Insect feces may contain a lot of stuff you don’t want in your body. One practical advice: wash your vegetables thoroughly before you eat them (like in salads or sandwiches) because frass is so tiny, you can overlook them.

Can I use caterpillar frass as fertilizer? Yes. It’s organic, with no harsh chemicals that can harm your plants.

Do insects fart? Insects only eat leaves, so gases in any insect fart would most likely be methane and hydrogen, both of which are odorless. Besides, insect fart would be so tiny, you’d probably never smell it.

Why would caterpillars fling their frass? Researchers don’t really know why, but the theory is that they’re probably throwing their waste far away so that enemies won’t know where they live, says Martha Weiss of Georgetown University.


Caterpillars don’t get much exercise and eat 40 times more food than their body weight. However, instead of becoming obese (like mammals do), they produce a lot of poop with so many nutrients, microorganisms, and biomolecules. Here are some uses of frass:

  1. For protection: Frass can be used to keep away pests or predators by shooting pellets, as cover shields, or as poop shields
  2. For nutrition: Frass allows caterpillars to feed on leaves, and excretion helps them absorb more nutrition and increase their body weight many times. Frass is also a promising source of probiotics and antioxidants.
  3. For communication: Frass is used for navigation to find their way home, to attract mates, as well as to deter enemies and predators.
  4. To soil enhancement: Frass can be used to improve the soil’s nitrogen content, reduce the use of fertilizers that can harm the environment, and keep away the eggs, spores, or the seeds of alien or invasive species.
  5. To strengthen plants: Frass contains biochemicals and biomaterials that strengthen the cell walls of plants, help plants resist nematode attacks and root rot, as well as promote plant growth and productivity.
  6. In scientific and medical research: There’s still a lot of undiscovered caterpillar species in the world, but the little that we know has already provided humanity with useful materials such as food (such as mopane in South Africa), clothing (silk in China), as well as alternative or promising treatments for cancer, pain, fever, and inflammation.

And that’s it! You’ve just reviewed the scoop on frass and how it can be used in so many ways. Happy gardening!

Do you know of other ways that caterpillar poop can be used? Let me know!

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