Feeding guide

How to gut load feeder insects

By The Bug Cartel · 7 min read · Every fact cited

To gut load feeder insects, give them a dry, high calcium diet and a safe moisture source for 24 to 48 hours before they go to your reptile. Studies show this raises the calcium in crickets, mealworms and dubia roaches within that window. Gut loading does not fix every nutrient gap, so most keepers also dust insects with a calcium supplement just before feeding.

What is gut loading?

Gut loading means feeding insects a diet rich in the nutrients your reptile needs, shortly before the insects are eaten. The food sits in the insect's gut, so the reptile eats it too.1

The main target is calcium. Most insects hold less than 0.3% calcium on a dry matter basis because they have no mineralized skeleton.1 In one analysis of commercially raised feeders, every sample fell short of the calcium and vitamin D3 standards the author used.11 Calcium, vitamin A and vitamin D deficiencies are the three most commonly reported problems in captive insectivores.1

What gut loading can and cannot change

What the studies show it can do

  • Raise calcium. Gut load diets with 4% to 9% calcium raised the calcium content of wax moth larvae, house crickets, mealworms, superworms and silkworms in several studies.1 In crickets, body calcium and vitamin A rose in a straight line as the diet's calcium or vitamin A rose.2
  • Turn the calcium to phosphorus ratio positive in dubia roaches. Fasted dubia nymphs had a ratio below 0.2 to 1. After 24 hours on a high calcium diet, the ratio was 1.5 to 1.3
  • Raise vitamin A in crickets, mealworms, black soldier fly larvae and silkworms.18
  • Add carotenoids. Carrots or other produce offered during the last 24 hours before feeding raise carotenoids, though how much an insect stores varies by species.1

What it cannot do

  • Fix a low calcium food. In the 2025 dubia study, a high moisture diet sold as balanced left the ratio at about 0.19 to 1, no better than fasted roaches.3 The authors warn that gut load labels are not strictly regulated.3
  • Rebuild the whole insect. Apart from calcium and iron, and protein in adults, neither diet in that study changed the overall nutrient content of the roaches.3
  • Make more always better. Too much calcium can reduce absorption of other minerals, and too much vitamin A or D can be toxic.1

How long to gut load

Across studies, gut loading for 24 to 72 hours gives similar nutrient levels in most insects.1 Results differ by insect, diet and temperature. Feeding some diets for more than two days lowered the calcium gain, possibly because the insects found the diet less palatable.1 Feeding gut load diets for long periods can also harm the insects.1

Gut loading times used in published studies
Insect What the study found
Dubia roaches Calcium to phosphorus ratio of 1.4 to 1 at 12 hours, 1.7 to 1 at 24 hours and 2.1 to 1 at 48 hours on an 8.3% calcium diet. The author recommends 24 hours.4
House crickets 48 hours raised the ratio, and 72 hours added nothing more. Another study found calcium highest after one day.1
Mealworms and superworms Two days on a high calcium cricket feed raised calcium enough to meet a laboratory rat calcium standard.7
Black soldier fly larvae 24 hours recommended for gut loading vitamin A.8

Timing after gut loading matters less than many keepers fear. Gut-loaded dubia showed no change in protein, fat or dry matter over 12 hours without food.9 In a small trial, adult dubia kept a positive calcium to phosphorus ratio for 72 hours after a 24 hour high calcium feeding.3 Still, remove feeders your animal has not eaten within 12 hours, or give them gut load food your reptile cannot reach.9

Best gut load diet

Look for a dry commercial gut load with calcium in the 4% to 9% range that the studies used.1 For crickets, one study worked out target levels of about 5.1% calcium for adults and 3.2% for nymphs, with added vitamins A, D and E.2 Read the label for a calcium figure. The review authors recommend lab analysis of commercial diets because their real calcium content can differ from the label.1

What to gut load dubia roaches with

The dubia studies used a dry, high calcium roach diet with 8.3% calcium on a dry matter basis.4 Before testing, researchers kept the roaches on pieces of sweet potato for food and moisture.3 A UK study gut loaded dubia for 48 hours on a dry diet with diced potato and soaked cotton wool.9 Our dubia roach care guide covers daily feeding and bin setup for dubia roaches you hold before feeding out.

Safe foods and foods to avoid

The produce used in gut loading studies includes carrots, sweet potato and potato.139 Carrots are a well accepted food and moisture source for many feeder insects.1 In the UK study, researchers replaced food and water every 24 hours to stop mold growing.9

We found no controlled study that tested which vegetables to keep out of a gut load. Lists of foods to avoid, such as spinach for its oxalate, come from hobby sources rather than feeding trials. Until better data exists, stick to a tested high calcium diet plus simple produce.

How you offer the diet also matters. Earlier work found 100% mortality in superworms and 30.7% in mealworms when a high calcium diet was used as bedding for 48 hours. Mortality fell below 1% when the same diet was served in a dish.3 Serve dry gut load in a shallow dish.

Water sources

Dry gut load diets have little moisture. Researchers think dehydration on a dry diet can kill feeder insects.3 Give a moisture source that insects cannot drown in.

  • Fresh produce such as carrot or sweet potato.13
  • Cotton wool soaked in water, which the UK study gave to dubia.9
  • For crickets, a water container with tissue paper in the opening, which one study used to prevent drowning.12

Gut loading vs dusting

Dusting means coating insects in a fine supplement powder just before feeding. It works, but the dose drops fast. House crickets can groom off half the powder in 150 seconds.1 In another test, dust added 13.4% to a cricket's weight right after dusting, 8.7% after 15 minutes and 4.5% after 30 minutes.1 A third study found that dusting kept the calcium to phosphorus ratio above 1 to 1 for up to 5.5 hours in two cricket species, except adult black field crickets.6

Dust is hard to measure, and small insects carry more dust for their size than large ones.1 Gut loading delivers calcium inside the insect, but it may not reach the levels an insectivore needs. A review of cricket studies concluded that both gut loading and dusting appear necessary.5 That is why most keepers do both. Dusting with a multivitamin is also one way to supply vitamins A, D3 and E that black soldier fly larvae lack.8 Ask a reptile vet how often to dust for your species, and see a vet for signs of illness.

Which feeders gut load well

Crickets and dubia roaches

Both respond well. In crickets, calcium and vitamin A track the diet closely.2 Dubia reached a positive calcium to phosphorus ratio within 12 hours on a high calcium diet.4 For sizing dubia to your animal, see our dubia roach size chart.

Waxworms

High calcium diets have raised the calcium content of wax moth larvae.1 The bigger issue is fat. Waxworms were deficient in more nutrients than any other feeder in one analysis.11 Their high fat and low moisture mean they fall short on more nutrients for their energy than crickets do. The same author advises that well supplemented, lower fat insects should form most of an insectivore's diet.10 Treat waxworms as an occasional food.

Gut loading black soldier fly larvae

Black soldier fly larvae differ from most feeders because they carry calcium in their exoskeleton. Commercial larvae measured 2.14% to 3.14% calcium on a dry matter basis, with more calcium than phosphorus.1 They still lack meaningful vitamins A, D3 and E. Vitamin A gut loading works in larvae, and the study authors recommend 24 hours.8

Gut loading stops working near pupation. Prepupae empty their gut before they pupate.1 Animals that swallow larvae whole may also absorb less of their calcium. In one frog study, calcium digestibility was 44% for whole larvae against 88% for mashed larvae.1 Our guide to black soldier fly larvae for reptiles covers how to use them, and you can order black soldier fly larvae in counts of 250 to 1000.

For a full feeding plan built on these insects, see our guide to the best feeder insects for bearded dragons.

Sources

  1. Finke MD, Oonincx DGAB. 2023. Insects as food for insectivores. Chapter 18 in Mass Production of Beneficial Organisms, 2nd edition, pages 511 to 540. Elsevier.
  2. Finke MD. 2003. Gut loading to enhance the nutrient content of insects as food for reptiles: a mathematical approach. Zoo Biology 22, pages 147 to 162.
  3. Barras E, Boykin KL, Aguilar MG, Lex Z, Bitter A, Mitchell MA. 2025. Effect of commercial diets on the nutritional value and mortality rates of dubia roaches (Blaptica dubia). Journal of Herpetological Medicine and Surgery 35(3), pages 176 to 191.
  4. Barras E. 2023. Assessing the nutritional value of dubia roaches (Blaptica dubia) as a feeder insect in reptiles. Master of Science thesis, Louisiana State University.
  5. Livingston S, Lavin SR, Sullivan K, Attard L, Valdes EV. 2014. Challenges with effective nutrient supplementation for amphibians: a review of cricket studies. Zoo Biology 33(6), pages 565 to 576.
  6. Michaels CJ, Antwis RE, Preziosi RF. 2014. Manipulation of the calcium content of insectivore diets through supplementary dusting. Journal of Zoo and Aquarium Research 2(3), pages 77 to 81.
  7. Latney LV, Toddes BD, Wyre NR, Brown DC, Michel KE, Briscoe JA. 2017. Effects of various diets on the calcium and phosphorus composition of mealworms (Tenebrio molitor larvae) and superworms (Zophobas morio larvae). American Journal of Veterinary Research 78(2), pages 178 to 185.
  8. Boykin KL, Mitchell MA. 2021. Evaluation of vitamin A gut loading in black soldier fly larvae (Hermetia illucens). Zoo Biology 40(2), pages 142 to 149.
  9. Gorst VM, Mitchell K, Whitehouse-Tedd KM. 2015. Effect of post-gut loading time on the macro-nutrient content of three feeder invertebrate species. Journal of Zoo and Aquarium Research 3(3), pages 87 to 93.
  10. Finke MD. 2015. Complete nutrient content of four species of commercially available feeder insects fed enhanced diets during growth. Zoo Biology 34(6), pages 554 to 564.
  11. Finke MD. 2002. Complete nutrient composition of commercially raised invertebrates used as food for insectivores. Zoo Biology 21, pages 269 to 285.
  12. Oonincx DGAB, van Broekhoven S, van Huis A, van Loon JJA. 2015. Feed conversion, survival and development, and composition of four insect species on diets composed of food by-products. PLoS ONE 10(12): e0144601.

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