Black soldier fly larvae for reptiles

Black soldier fly larvae (BSFL) are a useful feeder for insect-eating reptiles and amphibians. They carry more calcium than most feeder insects because their skin holds calcium carbonate. In a leopard gecko study, the geckos absorbed only about 43% of that calcium. Feed BSFL as one part of a varied diet, keep calcium dust and UVB in place, and store the larvae at room temperature.

Why are black soldier fly larvae high in calcium?

The black soldier fly is Hermetia illucens. Its larvae build calcium carbonate into their cuticle, the outer skin. Young larvae already carry it, mostly in an amorphous form, and the share of crystalline calcite rises as they grow.¹ The larvae also store calcium carbonate granules in a pair of specialized Malpighian tubules, which the researchers call lime glands.¹ A mineralized cuticle is very rare in insects. Crabs and other crustaceans do it, but almost no insects do.¹

That calcium carbonate is why BSFL test higher in calcium than other feeder insects.² In one feeding trial, whole larvae held 2.9% to 3.5% calcium on a dry matter basis, depending on the calcium in their feed.² Analyses of crickets, mealworms, superworms and waxworms found all four to be poor sources of calcium.³

BSFL calcium to phosphorus ratio

Reptile nutrition looks at calcium against phosphorus. A ratio of 2:1 or higher is considered important for preventing nutritional secondary hyperparathyroidism, the bone disease often called metabolic bone disease, in insect-eating reptiles.⁴ BSFL are often cited at about 2.5:1, which makes them the only commercial feeder insect reported to potentially reach a positive ratio on their own.⁴

That number moves with what the larvae eat. Published ratios run from 0.3:1 to 14.9:1, depending on the rearing diet.⁴ A label or a single analysis tells you about one batch on one diet, not every cup of larvae.

Are black soldier fly larvae good for reptiles? What the gecko study found

High calcium in the larva does not mean high calcium in the animal. The best data come from a 2020 trial at Louisiana State University. Researchers fed 24 adult male leopard geckos nothing but BSFL for 140 days. The geckos got no calcium dust, and their lighting gave no UVB.⁴

• The geckos digested most nutrients well. Calcium was the exception, with a digestibility of 43%.⁴
• The authors wrote that the calcium-rich exoskeleton usually passed through the gut intact.⁴
• Blood calcium fell in every group over the trial. The authors named poor calcium digestibility, low vitamin D, or the end of calcium supplements given before the trial as possible causes. Blood work also showed possible deficits developing in sodium and total protein.⁴
• After correcting for digestibility, the authors estimated the diet still supplied enough calcium on paper for a growing gecko. They advised caution anyway, because needs vary between animals.⁴

The authors concluded that more research is needed to know whether BSFL supply enough calcium without supplements.⁴ That is the honest state of the evidence. BSFL are a good source of calcium compared with other feeders. No study has shown that they meet a reptile's calcium needs on their own.

Do BSFL need calcium dusting?

The research does not settle it. The gecko study authors said they did not have enough data to recommend for or against calcium supplementation with BSFL.⁴ Calcium dust is cheap, and the only controlled trial could not rule out a shortfall. Dusting BSFL on the same schedule you use for other feeders is the cautious choice until better data exist. Your reptile vet can set that schedule for your animal.

Vitamin D is a separate problem. Analyses of soldier fly larvae and other feeders list vitamin D among the nutrients most likely to be short when insects feed insectivores.⁵ The gecko study authors note that most feeder insects, BSFL included, are low in the fat-soluble vitamins.⁴ A calcium-only dust does not fix that.

Do you still need UVB with BSFL?

Yes. The Merck Veterinary Manual lists lack of UVB light and too little heat as causes of nutritional secondary hyperparathyroidism, alongside a poor calcium to phosphorus ratio and low vitamin D3.⁶ Calcium in the food does not replace UVB. Keep the lighting your species needs. If your reptile stops eating, has a swollen jaw or limbs, twitches, or cannot walk normally, see a reptile vet.⁶

Can BSFL be the only feeder?

No. The gecko trial was the closest test of a BSFL-only diet, and it found possible calcium, sodium and protein deficits building over time.⁴ Its authors state that insectivores should always get a varied diet to limit nutritional deficiencies.⁴ Rotate BSFL with a second staple such as dubia roaches.

Gut loading helps too. In the same study, larvae fed a vitamin A diet for 24 hours raised vitamin A levels in the geckos that ate them.⁴ Our guide on how to gut load feeder insects covers what to feed and for how long.

Which reptiles and amphibians eat BSFL?

BSFL are a popular feeder for insect-eating reptiles and amphibians.⁴ Keepers offer them to lizards such as leopard geckos and bearded dragons, to chameleons, and to frogs. The only controlled feeding trial in a pet reptile used leopard geckos.⁴ We found no published feeding trial of BSFL in chameleons, bearded dragons or pet frogs, so the gecko results are the best guide for now.

For species-specific diets, see the best feeder insects for bearded dragons and the best feeder insects for leopard geckos.

How many BSFL to feed

No veterinary source or published study gives a count of BSFL per meal for any reptile. Here is what the research does show.

In the leopard gecko trial, researchers offered larvae weighing 5% of each gecko's body weight, three times a week. The geckos ate a little over half of what was offered, about 2.7% of body weight per meal.⁴ That was a research protocol with BSFL as the only food, not a feeding recommendation.

In practice, use BSFL as part of the insect portion your species guide or vet already sets. Offer a few at a time, watch what your animal eats, and remove larvae it ignores. The bearded dragon and leopard gecko guides above give meal frequencies by age.

How to store BSFL

Keep black soldier fly larvae at room temperature in the cup they arrive in, away from heaters and sunny windows. You do not need to feed them.

Why BSFL do not need food

Larvae near the end of the larval stage stop eating. At this point they are called prepupae. Prepupae turn darker than younger larvae, stop feeding, avoid light, and look for a sheltered spot to pupate.⁷ The University of Florida describes the last larval stage leaving the food to find a dry, sheltered place before pupation.⁸ Dark larvae in your cup are in this stage.

Should you refrigerate BSFL?

Cold storage has a short limit. In a 2025 study of bulk farm larvae, live larvae stored at 43 to 50 F (6 to 10 C) kept losses under 15% only for periods shorter than six days. Of the temperatures tested, 50 F (10 C) kept them alive longest.⁹ We do not recommend the refrigerator.

BSFL turn into flies if kept warm long enough

BSFL are fly larvae, and warmth moves them along. According to the University of Florida, the larvae take about 14 days to develop through six stages, and pupation then takes about two weeks.⁸ In a lab study, development took about four days longer at 81 F (27 C) than at 86 F (30 C).¹⁰ A cooler room likely slows them further, though no study has measured how long a cup of feeder larvae lasts on a shelf. Buy an amount your animals will finish in a few weeks.

If a few flies do hatch, they are harmless. The adult flies have no stinger, and they do not need to feed because they live on fat stored as larvae.⁸

More answers on storage and orders are in the feeder FAQ.

Sources

1. Rebora M, Salerno G, Piersanti S, Saitta V, Morelli Venturi D, Li C, Gorb S. 2023. The armoured cuticle of the black soldier fly Hermetia illucens. Scientific Reports 13:22101.
2. Do S, Koutsos EA, Utterback PL, Parsons CM, de Godoy MRC, Swanson KS. 2021. Amino acid digestibility and digestible indispensable amino acid score-like values of black soldier fly larvae fed different forms and concentrations of calcium using the precision-fed cecectomized rooster assay. Journal of Animal Science 99(6):skab124.
3. Finke MD. 2015. Complete nutrient content of four species of commercially available feeder insects fed enhanced diets during growth. Zoo Biology 34(6):554 to 564.
4. Boykin KL, Carter RT, Butler-Perez K, Buck CQ, Peters JW, Rockwell KE, Mitchell MA. 2020. Digestibility of black soldier fly larvae (Hermetia illucens) fed to leopard geckos (Eublepharis macularius). PLoS ONE 15(5):e0232496.
5. Finke MD. 2013. Complete nutrient content of four species of feeder insects. Zoo Biology 32(1):27 to 36.
6. Divers SJ, Comolli JR. Nutritional, metabolic, and endocrine diseases of reptiles. Merck Veterinary Manual, Merck and Co. Full review 2025.
7. Giannetti D, Schifani E, Reggiani R, Mazzoni E, Reguzzi MC, Castracani C, Spotti FA, Giardina B, Mori A, Grasso DA. 2022. Do it by yourself: larval locomotion in the black soldier fly Hermetia illucens, with a novel "self-harvesting" method to separate prepupae. Insects 13(2):127.
8. Diclaro JW II, Kaufman PE. Black soldier fly Hermetia illucens Linnaeus (Insecta: Diptera: Stratiomyidae). Featured Creatures EENY-461, University of Florida IFAS Extension.
9. Resconi A, Biasato I, Bellezza Oddon S, Loiotine Z, Gasco L. 2025. Storing live black soldier fly larvae: the influence of temperature and storage techniques. Animal 19:101605.
10. Tomberlin JK, Adler PH, Myers HM. 2009. Development of the black soldier fly (Diptera: Stratiomyidae) in relation to temperature. Environmental Entomology 38(3):930 to 934.