Nutrition Guide Feeder Insects: Mealworms & Beetles

Mealworms Pros and Cons

Tenebrio molitor typically known as mealworms and darkling beetles can be part of a balanced diet for your bearded dragon at pupae, mealworms and beetle stages. Mealworms offer variety, but moderation is key.

Feeding large quantities of mealworms or relying solely on them has been shown to cause calcium deficiency such as found in a study by Klasing et al., (2000) on chicks and may cause metabolic bone disease in reptiles (MBD) (Brown, 2012). This is frequently raised as a concern by vets around the world for reptiles. For reptiles with MBD, consult your vet before feeding mealworms.

Key Points

Mealworms and darkling beetles (Tenebrio molitor) can be part of a balanced bearded dragon diet, but overfeeding can lead to health issues.

• The nutritional value of mealworms varies depending on their diet.
• Mealworm larvae have a high fat content and low calcium to phosphorous levels.
• Proper preparation and feeding techniques, such as gut-loading, can enhance the benefits of mealworms in reptile diets.
• Mealworms should only make up a small portion of a bearded dragon’s diet, and beetles can also provide variety.
• Mealworms should be fed after molting.
• Research supports gut-loading and feeding mealworms in moderation to improve their nutritional balance and prevent health issues.

Natural Stimulation Value

Mealworm pupae are limited to an occasional wriggle; they don’t offer your bearded dragon a chance to fully interact with its environment and encourage natural behaviors. Larva can wriggle around, and beetles can move faster. Beetles may also provide some benefit for the bearded dragons teeth by aiding in cleaning.

The Nutrient Value of Tenebrio molitor as Mealworms & Beetles

Finke (cited in Van Huis et al, 2013) compared the nutritional value of mealworms (dry weight, fasted 24 hours) to beef and found:

• The fat content of mealworms is less than beef, but beef had slightly higher protein.
• Mealworms had higher vitamin content except for B12.
• Mealworms had similar potassium, iron, zinc and other minerals.
• Numerous variations in amino acids and fatty acids between beef and mealworms.

Barker et al., (1998) and Oonincx & Dierenfeld, (2011) assessed the nutrient value of the mealworm as dry matter as:

• Calcium: Regular mealworms and supermealworms have low calcium levels, around 0.12%.
• Phosphorus: Phosphorus levels are relatively high across all mealworm types, ranging from 0.83% to 1.42%, contributing to an imbalanced calcium-to-phosphorus (Ca:P) ratio.
• Fat: The Tenebrio beetle has 1/2 of the fat content that its larval stage has.
• Vitamins: Overall, the levels of fat-soluble vitamins and nutrients in beetles are low.
  • Vitamin E: Regular mealworms and supermealworms have moderate Vitamin E content, approximately 30-32 IU/kg.
  • Vitamin A: Vitamin A content varies, with regular mealworms at about 811 IU/kg DM and supermealworms at 972 IU/kg.
• Protein: Tenebrio beetles have a higher protein content (51%) than in their larval stages. This is likely due to the beetles’ more developed exoskeletons, which could also make them harder to digest.
• Chitin (as NDF): Chitin content, indicative of dietary fiber, is present in mealworms, with a percentage of around 15% of, contributing to gut health but also potentially affecting protein digestibility.

Finke (2002) assessed the nutrient value of mealworms as is (in their wet form) to be:

Nutrient/Mineral (per 100 grams)	Mealworm larvae	Adult Mealworms
Weight (mg per insect)	126	136
Moisture (g)	61.9	63.7
Protein (g)	18.7	23.7
Fat (g)	13.4	5.4
NFE (g)	2.7	-1.4
Neutral Detergent Fiber (NDF) (g)	5.7	11.5
Acid Detergent Fiber (ADF) (g)	2.5	7.4
Ash (g)	0.9	1.2
Metabolizable Energy (kcal/g)	2056	1378
Calcium (mg)	16.9	23.1
Phosphorus (mg)	285.0	277.0
Ca:P Ratio	0.06:1	0.08:1
Magnesium (mg)	80	61
Sodium (mg)	54	63
Potassium (mg)	341	340
Iron (mg)	2.1	2.2
Manganese (mg)	0.5	0.4
Vitamin A (IU)	< 100	< 100
Vitamin D3 (IU)	< 25.6	< 25.6
Vitamin E (IU)	< 0.5	<0.5
Methionine (g)	2.4	3.0
Vitamin B12 (mg)	0.5	0.6
Thiamin (mg)	0.2	0.1

Concerns with Feeding Mealworms

The main concerns with feeding mealworms are:

• Poor calcium to phosphorus ratio: Take it to an acceptable level with the right diet and gut loading of the meal worm.
• Fat content: Mealworms diet will have some influence on the level of fat, however mealworms by nature will have a significant amount of fat. Mealworms should make up no more than 10% of the diet (Brown, n/d).
• Level of chitin: Feed small mealworms or those that have just shed, they will have a much lighter skin color (Brown, n/d).

How many Mealworms to Feed a Bearded Dragon?

The following calculations provide a guide on the number of mealworms that can be fed to your bearded dragon in a single meal:

Bearded Dragon Stage	Body Weight	Total Invertebrates in Diet by Weight	Total Tenebrio molitor by Weight	Mealworm Count	Beetle Count
Juvenile	150 gm	5.25 gm	1.05 gm	8-9 mealworms	7-8 beetles
Young Adult	375 gm	3.75 gm	0.75 gm	6 mealworms	5-6 beetles
Adult	450 gm	2.25 gm	0.45 gm	4 mealworms	3-4 beetles

These calculations are based on the:

• Mealworms are harvested at a young, small age around 0.12 gm.
• Tenebrio molitor beetle weighing 0.136 grams.
• Maximum of 20% of mealworms within the invertebrate allowance.
• Insect requirements for bearded dragons.

Feeding Mealworms: Enhancing Nutritional Value with Diet and Gut Loading

Key Points:

• Mealworms are better fed Pollard than wheat germ which is also their housing substrate.
• A moisture source is required and usually provided through vegetation.
• Mealworms fed a cabbage, carrot, and flaxseed diet have improved nutritional value.
• Vegetable mix may be an all-round suitable wet feed.
• Feeding potato may increase the fat content dramatically.

The nutritional composition of mealworms is directly influenced by the diet they are reared on and finally by their gut loading.
Their diet is specific to the insect being kept and should focus on promoting their health while being tailored to deliver the specific nutritional benefits we want for our reptiles.

On the other hand, gut loading applies to all insects. What to gut load mealworms with is later in this article.

Diet of the Tenebrio molitor (Mealworm)

Mealworms typically thrive on dry feeds, such as wheat germ, and require moisture, which is often provided through vegetables. However, different feeds have a significant impact on the nutritional quality of the mealworms.

A suggested wet diet for mealworms shown to improve their overall nutritional value is:

• Cabbage,
• Carrot, and
• Flaxseed (or flax oil).

In addition, Brown (n/d) recommends using Pollard or Mill Runs for the dry feed because they have lower levels of phytic acid. Phytates in bran or whole grains can bind with calcium and magnesium, making these minerals hard for reptiles to absorb. Even if calcium is present, it won’t be absorbed if mealworms are fed high-phytate diets.

Pollard and Mill Runs come from the inner parts of grains and contain fewer phytates. This makes them better for gut-loading. By feeding mealworms these products, reptiles can absorb more calcium, reducing the risk of health issues like metabolic bone disease. Using normal cereal products, like bran, can prevent reptiles from getting the calcium they need for healthy bones.

Research on the Impact of Different Feeds on Mealworm Nutrition

Some feeds are better than others. A study by Noyens et al., (2023) experimented with some wet feeds to add to the dry wheat bran feed to supply moisture. Regardless of the wet feed the only mineral content that improved in the mealworms was calcium, iron and manganese. On potato cuttings they:

• Doubled their fat,
• Reduced their macro and microminerals, and
• Increased their unhealthy fats (saturated and mono-unsaturated fats) while reducing their healthy fats (called poly-unsaturated fats).

Wet Feed Type	Vegetable Mix	Potato Cuttings
P (mg/100g DM)	939	690
Mg (mg/100g DM)	297	165
K (mg/100g DM)	1128	891
Na (mg/100g DM)	105	96
Ca (mg/100g DM)	28	2
Ca: P Ratio	0.03:1	0.003:1

Dragojlović et al., (2022) found that wet feeds (in addition to the dry feeds) altered nutrient composition of mealworms:

• Carrots reduced fat content and increased crude fibre.
• Cabbage improved most amino acid content although it had a negative effect on methionine.
• Flaxseed increased alpha-linolenic acid (ALA), an omega-3 fatty acid, by 10 times and the balance between omega-6 and omega-3 fatty acids was lowered to a favorable ratio of 2.
• Cabbage, carrot and flaxseed resulted in the mineral content of mealworms improving.

Bordiean et al., (2022) also found that the addition of flax cake (specifically flax oil) to the mealworms’ diet balanced the omega-6 and omega-3 fats in the mealworms more favorably. Essentially, feeding mealworms flax cake helped make them healthier to eat from a human’s perspective by improving the balance of good fats inside them.

Mealworms fed with potato cuttings doubled their fat content and increased saturated and mono-unsaturated fatty acids.

Noyens et al., (2023)

Gut Loading Mealworms

Naturally, mealworms are low in calcium and high in phosphorus, which can bind essential minerals, making them unavailable for use in your pet’s diet. For tailored information to suit your specific reptile and its needs, especially if there are underlying health issues, discuss gut loading with your vet.

Mayer (2014) recommends calcium content for gut-loading mealworms at 9% (or 9 g of calcium per 100 g of mealworms). It’s crucial not to exceed 12%, as mealworms may avoid food with higher calcium concentrations, reducing their overall activity (Mayer, 2014).

Based on 10 small mealworms (each weighing 0.12 grams) at 9% calcium that would equate to 0.108 grams of calcium per 100 grams of mealworms. A pinch of calcium will weigh around 0.3 grams, so this means you need 1/3 of a pinch of calcium.

Mealworm Type	Weight per 10 Mealworms (g)	Calcium Needed (g)	Pinch Equivalent
Small Mealworms (10)	1.2	0.108	1/3 of a pinch
Average Mealworms (10)	1.26	0.113	1/3 of a pinch
Beetles (10)	1.36	0.122	1/3 of a pinch

To enhance the nutritional value of mealworms, Finke (2003) also recommends a range of vitamins (see table below). However, sourcing a multivitamin for home use that matches these ratios is unlikely. A good quality multivitamin with a broad spectrum of nutrients should suffice for meeting most of the gut-loading needs. Use multivitamins at the rate recommended by the manufacturer.

For gut loading purposes with mealworms, less than a pinch per 10 mealworms should be adequate. Insects are dusted with both calcium and multivitamin powders before feeding according to schedules. Again, see manufacturers instructions.

Mealworm Type	Small Mealworms (10)	Average Mealworms (10)	Beetles (10)
Weight per 10 Mealworms (g)	1.2	1.26	1.36
Iron (mg)	0.061	0.064	0.069
Manganese (mg)	0.037	0.039	0.042
Vitamin A (µg)	15.972	16.771	18.102
Vitamin D (µg)	0.552	0.58	0.626
Vitamin E (mg)	0.792	0.832	0.898
Thiamin (mg)	0.006	0.006	0.007
Vitamin B12 (µg)	0.78	0.819	0.884
Methionine (g)	0.035	0.037	0.039

Several studies support the value, success, and timing of gut loading:

• Latney et al. (2017) achieved a calcium to phosphorus ratio of 1.3:1 by using a calcium-enriched cricket diet.
• Klasing et al. (2000) successfully added 8% calcium to a broiler mix for chicks, improving the calcium to phosphorus ratio within 24 hours when mealworms were fed a calcium-supplemented substrate.
• Anderson (2000) also demonstrated that within 24 hours, mealworms could increase their calcium to phosphorus ratio using a calcium-fortified commercial diet.

Additionally, research by Gorst et al. (2015) showed that even when mealworms were starved for 12 hours, they retained their nutrient value, maintaining calcium levels in their gut for at least a day after gut loading.

Do mealworms Cause Impaction in bearded dragons?

There is potential for bearded dragons to be constipated or impacted from mealworms given the wrong conditions. Wright, et al., (2008) and Brown (2012) discusses some of those conditions being:

• Incorrect food items including too many mealworms especially:
  • If not gut loaded to improve deficiencies in nutritional value, and
  • Fed at the wrong stage of the mealworm’s life. After molting is ideal.
• Insufficient roughages (e.g. greens),
• Poor environment conditions such as incorrect heat and humidity,
• Dehydration,
• Insufficient exercise,
• History with metabolic bone disorder.

As a matter of interest, chitin is used in a wide range of applications. It has anti-bacterial, anti-viral and anti-fungal properties which make it useful in medical and health care products such as drug capsules, wound healing products and prebiotics. Other applications chitin has also been found to be useful for include wastewater treatment, bioenergy, agriculture and absorbing pollutants (Khoushab and Yamabhai 2010).

Conclusion on the Value of Mealworms in the Diet

Mealworms are just one of the insects bearded dragons can eat. When fed in moderation and properly gut-loaded, they can be a valuable addition to your bearded dragon’s diet. Their high fat content and poor calcium-to-phosphorus ratio mean they should never be the primary food source. By carefully managing their diet, incorporating a variety of feeders, and focusing on gut-loading, you can enhance the nutritional value of mealworms. It is crucial to balance their intake with other insects that offer better calcium levels and lower fat content. By doing so, you can promote a healthier, more balanced diet for your bearded dragon, reducing the risk of metabolic bone disease and other health issues.

References

• Anderson, S. J. (2000). Increasing calcium levels in cultured insects. Zoo Biology, 19, 1–9.
• Arnold Van Huis, Itterbeeck, J. V., Klunder, H., Mertens, E., Halloran, A., Muir, G., & Vantomme, P. (2013). Edible insects : future prospects for food and feed security. Food And Agriculture Organization Of The United Nations.
• Bordiean, A., Krzyżaniak, M., Aljewicz, M., & Stolarski, M. J. (2022). Influence of Different Diets on Growth and Nutritional Composition of Yellow Mealworm. Foods, 11(19), 3075.
• Brown, D. (n.d.). The Pro’s and Con’s of Mealworms as a food for reptiles. Dr Danny Brown BVSc(Hons) BSC (Hons) MACVSc (Avian Health).
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• Doneley, B., Monks, D., Johnson, R., & Carmel, B. (2017). Reptile Medicine and Surgery in Clinical Practice. Chichester, Uk John Wiley & Sons, Ltd.
• Dragojlović, D., Đuragić, O., Pezo, L., Popović, L., Rakita, S., Tomičić, Z., & Spasevski, N. (2022). Comparison of Nutritional Profiles of Super Worm (Zophobas morio) and Yellow Mealworm (Tenebrio molitor) as Alternative Feeds Used in Animal Husbandry: Is Super Worm Superior? Animals, 12(10), 1277.
• Finke, M. D. (2002). Complete nutrient composition of commercially raised invertebrates used as food for insectivores. Zoo Biology, 21(3), 269–285.
• Finke, M. D. (2003). Gut loading to enhance the nutrient content of insects as food for reptiles: A mathematical approach. Zoo Biology, 22(2), 147–162.
• Khoushab, F., & Yamabhai, M. (2010). Chitin Research Revisited. Marine Drugs, 8(7), 1988–2012.
• Klasing, K. C., Thacker, P., Lopez, M. A., & Calvert, C. C. (2000). Increasing the calcium content of mealworms (Tenebrio molitor) to improve their nutritional value for bone mineralization of growing chicks. Journal of Zoo and Wildlife Medicine, 31(4), 512–517.
• Latney, L. V., Toddes, B. D., Wyre, N. R., Brown, D. C., Michel, K. E., & Briscoe, J. A. (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), 178–185.
• Linggawastu Syahrulawal, Magnhild Oust Torske, Rumakanta Sapkota, Geir Næss, & Prabhat Khanal. (2023). Improving the nutritional values of yellow mealworm Tenebrio molitor (Coleoptera: Tenebrionidae) larvae as an animal feed ingredient: a review. Journal of Animal Science and Biotechnology, 14(1).
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• Noyens, I., Schoeters, F., Van Peer, M., Berrens, S., Goossens, S., & Van Miert, S. (2023). The nutritional profile, mineral content and heavy metal uptake of yellow mealworm reared with supplementation of agricultural sidestreams. Scientific Reports, 13(1), 11604.
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• Rumbos, C. I., & Athanassiou, C. G. (2021). The Superworm, Zophobas morio (Coleoptera:Tenebrionidae): A “Sleeping Giant” in Nutrient Sources. Journal of Insect Science, 21(2).
• Victoria Marie Gorst, Mitchell, K., & Whitehouse-Tedd, K. M. (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), 87–93.
• Wright, K. (2008). Two Common Disorders of Captive Bearded Dragons (Pogona vitticeps): Nutritional Secondary Hyperparathyroidism and Constipation. Journal of Exotic Pet Medicine, 17(4), 267–272.