Mealworms can eat just about anything: fruit, vegetables, dry grains, food waste - even cardboard and plastic! But to get the most nutrition for your pet, you probably want to avoid the all-plastic diet.

Investigations into mealworm diet.

Many studies have looked at how diet affects mealworm growth and survival, showing that the type of food is less important than the nutrients they get. 

A study on the effect of food types found that, when nutritional needs are met, diet has no major effect on insect performance, productivity or larval growth, with only slight (less than 1 mg) changes in larvae weight found.

Investigating protein to carbohydrate ratio, researchers found that giving mealworms a protein biased diet reduced their lifespan compared to an equal ratio. When given a choice of food, mealworms chose to eat a carbohydrate biased diet.

Common feed is dry grains - wheat bran, barley, millet grain, corn starch, etc. While mealworms can survive on bran, it won’t be a very balanced diet. Adding proteins, fats, moisture, carbohydrates and vitamin supplements will improve the insect’s growth - researchers found that supplementing a wheat diet with 10% yeast protein led to a larval weight gain of 50 mg from 2 mg - a 1000% increase.

A large evaluation of over 40 feed types found that mealworms fed only on cereal flours (Wheat, Barley, Corn, Millet, Semolina, Rye) for 1 week had low mortality rates of less than 10%. Interestingly, using oat flour raised mortality to 16%.

Legumes only diets caused high mortality in mealworms, even though they had the highest protein content – chickpea flour, fava bean flour and lentil flour all increased mortality above 15%. Mealworms fed on soybean flour grew less and created less larvae due to an enzyme inhibitor that disrupted digestion.

Milk based feed led to high (48%) mortality, but larvae production was high, making a larger mass of mealworms compared to the other feeds. 

 

The foods that gave the best growth:

• Wheat bran
• Hen feedb
• Buckwheat
• Rye flour.

What about food waste?

A study into 3 household wastes (Banana peel, Watermelon rind & Eggshells) found that food waste increased the fat content of mealworms. Fruit waste increased survival rate compared to eggshells or bread. Watermelon waste was the best for mealworm growth with banana peel a close second.

A high percentage of mixed vegetable or garden waste isn’t beneficial for growing mealworms however as they decrease the concentration of protein and increase fat concentration, leading to increased mortality.

Can you feed them meat?

The recommendation is to treat mealworms as vegetarian creatures as meat isn’t their first choice and they could be affected by bacteria in the meat. In limited food situations they will resort to meat eating (and cannibalism). You can, however, feed them crushed pet food pellets, since they have a good balance of nutrients.

Do they drink water?

Mealworms absorb moisture from the air through their rectum and prefer a humid environment but they also need to get water through their diet for growth. Giving them a bowl of water risks drowning them, so wet vegetables like carrots or potatoes, or damp sponges are usually given along with their feed.

Keeping your pets healthy.

When feeding reptiles, mealworms shouldn’t be the only item in the diet to avoid impaction. Due to being low in calcium, reptiles must have extra supplements. Birds may also need calcium added into their diet to avoid thin or soft shell eggs. If a reptile is low in calcium they will develop rickets, a disease that causes muscle tremors, bone fractures and thin shelled eggs.

There are two methods to remedy this with mealworms - Gut loading and Dusting.

Gut loading is increasing the amount of calcium in the insect’s diet for a few days to increase the concentration of it in the gut, while dusting is coating the insect in supplement powder just before feeding your pets. Combining the two is the best way to make sure your pet doesn’t suffer from deficiencies. Calcium can be found in ground eggshells or oyster shells, or from calcium carbonate powder supplements.

Timing is important when gut loading. A study found that when gut loading with 8% calcium feed, small mealworms reached maximum calcium content after 2 days and large mealworms reached a maximum after 4 days. Another found that longer periods of feeding (1 week+) a fortified diet resulted in a lower calcium content in the mealworms. 

 

Diet can affect frass...

If you’re using mealworm frass, you should know that diet also has an impact on their frass composition. A study compared three diets:

• Diet A contained 66% carbohydrates, 6% fat and 28% protein; 
• Diet B contained 77% carbohydrates, 6% fat and 28% protein;
• Diet C contained 49% carbohydrates, 12% fat and 39% protein.

Diet C produced frass with more than double the nitrogen content of the other diets, but had less potassium and phosphorus, while Diet A was found to greatly increase plant resistance to natural stresses.

In summary...

dry grains like wheat bran, buckwheat or rye are a good base to feed your mealworms, but they should be complemented with a protein source like lentils or yeast to improve the nutrition for your pet. Protein should not be the majority of their diet. Adding fruit or vegetable waste like raw potatoes will provide necessary water, while all types of meat should be avoided. Mealworms fed to lizards and chickens should be supplemented with calcium by gut-loading or dusting with calcium powder if they aren’t already getting it through their diet.