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Nutritional Benefits of Black Soldier Fly Larva Frass - Critter Depot

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Black Soldier Fly Larvae Frass: The Best Nutrition Your Plants Can Get!

The larvae of black soldier flies make great feeder insects. They are loaded with protein, have thin exoskeletons, and can be gut-loaded with important nutrients for your pet. However, black soldier fly larvae produce another product which is valuable to gardeners, farmers, and anyone who wants to have healthy, happy plants. This product is called black soldier fly larvae frass, or BSFL frass.

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What is Black Soldier Fly Larvae Frass?

“Frass” is a term used to describe the castings (poop), leftover food, and exoskeletons left behind after all the larvae are removed from a compost pile. The frass, once dried, resembles a crumbly soil. However, frass is loaded with far more nutrients than ordinary soil. Frass is typically used as a fertilizer to stimulate plant growth. It can be used on the farm, in the home garden, or even on houseplants!

BSFL frass is an organic fertilizer, much like worm castings. However, BSFL frass has been shown to contain more nutrients than red worm castings. Therefore, you can use less of it to give your plants the same great, natural boost they need to grow strong and healthy. 

Why is BSFL Frass Loaded with Nutrients?

Black soldier fly larvae have enormous appetites, and rapidly convert food waste into castings. The larvae are much more active than red worms, and thus convert food scraps into fertilizer at a much more efficient rate. The larvae break down the tough fibers of plant material. At the same time, they release the bound nitrogen, phosphorus, and potassium locked within the decaying material. While they use a significant portion of these nutrients as they grow, they excrete an equal amount into the frass they produce.

Watch BSFL Eat a Chick-Fil-A Sandwich

If you want to see just how efficient these black soldier fly larvae are at converting food waste into fertilizer, check out this video showing the black soldier fly larvae eating a Chick-fil-A sandwich:


Nutrient Profile of BSFL Frass

NPK Levels

As they say, “The proof is in the pudding.” The pudding, in this case, is the N-P-K value of BSFL frass. N-P-K values are a common way of displaying the nutrient levels of different fertilizers. The N-P-K value of a fertilizer describes how concentrated the nutrients nitrogen (N), phosphorus (P), and potassium (K) are in any given fertilizer. 

The frass sold by The Critter Depot has an N-P-K value of 5:3:2. This means it is 5% nitrogen, 3% phosphorus, and 2% calcium. While this may not seem like a lot, compare these values to several types of manure and compost. Here are the NPK values of commonly used fertilizers:

  • Cow Manure = 0.6 : 0.4 : 0.5
  • Pig Manure = 0.8 : 0.7 : 0.5
  • Chicken Manure = 1.1 : 0.8 : 0.5
  • Average Homemade Compost = 0.5 : 0.2 : 0.8

As you can see, BSFL frass is way more concentrated than normal manure. It even beats homemade compost by 10 times the nitrogen, around 4 times the phosphorus, and more than 2 times the potassium! 

Other studies have also confirmed that frass has a high level of ammonia. While ammonia itself is not a nitrogen source accessible to plants, many microorganisms in the soil use ammonia to create forms of nitrogen that plants can use. When you use frass as a spreadable fertilizer, or when you use it to make a fertilizer ‘tea’, you add this ammonia to the soil. Healthy soils will use this ammonia to create more nitrogen, leading to more green, leafy growth in your plants!


Unlike normal manure and compost, BSFL frass contains chitin. Chitin is a protein found in the exoskeletons of insects. As the larvae eat the compost and grow into adults, they molt. The molting process leaves outgrown exoskeletons behind within the frass mixture. 

Because plants and insects have evolved together for millions of years, plants can detect the presence of chitin in the soil. The presence of chitin tells plants that insects are present. This causes your plants to drastically increase their defenses against insects. They grow stronger cell walls, reinforce their structure, and generally produce healthier and larger leaves. While this is a defense to insects, it also greatly increases the health and vitality of your plants!

Other Benefits of BSFL Frass

While your plants will definitely enjoy BSFL frass as an occasional fertilizer, there are several other great reasons to use it. First, frass is an organic product created entirely by the black soldier fly larvae and the microorganisms in their gut. Unlike commercial chemical fertilizers, frass is not produced in a laboratory, contains no harsh chemicals, and can actually decrease the pathogenic bacteria within manure!

Several studies have shown that BSFL frass shows a significant decrease in the amount of E. coli and Salmonella bacteria, compared to the chicken manure it was produced from. This is because the larvae actively destroy these pathogenic bacteria and digest them. This means that frass significantly reduces the chance that you will get a bacterial infection from your plant crops.

More than that, using frass is highly beneficial for the environment. Instead of thousands of pounds of food wasting away in a landfill and creating greenhouse gases, the waste is converted into both feeder insects and the perfect fertilizer. By using frass, you are also reducing your carbon footprint, decreasing the volume of landfill waste, and supporting sustainable food waste programs!

How to Use BSFL Frass

Using black soldier fly larvae frass is easy! There are two basic methods for using the frass, both of which produce great results! 

The first is to mix the frass directly into your top soil, peat moss, or perlite mixtures. Frass can be added in a ratio of 4 parts mixer (peat moss or soil) to 1 part frass. Then, you can use this soil to plant seedlings, transfer potted plants, or add extra nutrition to your garden.

Alternatively, you can create a “frass tea” by mixing half a cup of frass to a gallon of water. This tea is extremely potent and immediately gives your plants access to the nutrients within the frass. You can water your plants with this tea 1-2 times a month to ensure they are getting all the nutrients they need!

1 comment

  • Hello
    Can I feed my pigs with frass, if so, how and what benefit will it have to my animals?

    Mzikayise on

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