What Do Mealworms Eat? Mealworm Diet and Feeding Guide

Mealworms are flexible eaters, but a colony still needs more thought than a handful of random scraps. The most reliable home setup combines a dry grain-based food with small, regularly replaced pieces of produce for moisture. What you choose affects growth, survival, cleanliness and, to some extent, the composition of the larvae you eventually feed to an animal.

This guide focuses on feeding the colony. If you also need help choosing a container, separating life stages or harvesting without ending the colony, use our complete guide to raising mealworms at home.

What Do Mealworms Eat?

Yellow mealworms are the larvae of the darkling beetle Tenebrio molitor. In stored-food environments they are associated with grains and grain products, which explains why wheat bran is used so often in home and commercial colonies. They can consume a much wider range of plant and animal materials, but being able to eat something does not make it a good routine feed.

A practical colony diet has two jobs. The dry component provides most of the food and also gives the larvae a loose material in which to burrow. The fresh component supplies accessible moisture. Supplements can change the nutrient mix, but they should not turn the tray damp, sticky or difficult to clean.

Best Dry Foods for Mealworms

For a straightforward home colony, wheat bran is the easiest place to start. It is widely used as both food and substrate, remains loose when kept dry and can be sifted when frass begins to accumulate. A major review of insect-rearing methods identifies wheat bran as a standard mealworm feed, while a controlled comparison of 44 commodities found that it produced the highest total larval biomass among the non-flour cereal substrates tested. (1) (2)

That does not mean wheat bran is the only acceptable food. Rolled oats and oat bran are common in small colonies. Rye, barley, buckwheat and some complete feeds have also supported mealworms in controlled studies. Results vary because a feed's physical form and full nutrient profile matter, not just its protein percentage.

The 44-commodity study is a good example of why a single number can be misleading. Oat flour was associated with higher adult mortality in that experiment, yet it also produced many offspring. Egg-layer hen feed performed well on several growth measures, while protein-rich soybean meal performed poorly. Those results describe specific materials under controlled conditions. They do not prove that all oats are harmful, all poultry feeds are ideal or every high-protein ingredient will improve a home colony. (2)

Moisture Foods and Water

Mealworms need access to moisture, but they do not need a water bowl. Standing water creates a drowning risk, and wet substrate raises the chance of mold, mites and sour odors. A small piece of firm produce placed on top of the dry feed is easier to monitor and remove.

Carrot and potato are practical because they hold their shape. Squash, apple and similar foods can work too, although softer or sweeter produce may spoil more quickly. The amount matters more than building a long list of approved vegetables. Give only what the colony can use before the food deteriorates.

Mealworms can absorb some atmospheric moisture, but research colonies still perform better when they receive an accessible moisture source. In one large feed trial, potato slices were supplied twice a week; the authors also observed poorer adult survival and reproduction when a water source was absent. (2)

How Often to Feed Mealworms

There is no useful one-size-fits-all portion. A tray of mature larvae in warm conditions consumes food much faster than a small group of young larvae. Use the colony itself as the measure.

• Keep dry food available: top up the grain base when it has been visibly reduced or frass begins to dominate it.
• Check moisture food daily: replace it when eaten and remove it as soon as it becomes slimy, moldy or buried in damp substrate.
• Start small: one or two modest pieces are easier to manage than a tray covered in vegetables.
• Adjust to the room: warm trays and large colonies usually need more frequent checks, while humid rooms make spoilage more likely.

A fixed schedule can help you remember the tray, but it cannot tell you whether yesterday's carrot is still safe. Look, smell and remove before adding more.

What Not to Feed Mealworms

The safest rule is to use clean, recognizable feed ingredients. Mealworms may investigate almost any organic material, but a feeder-insect colony should not double as an unrestricted waste bin.

• Moldy or rotten food: remove it along with any damp substrate touching it.
• Seasoned, salty, oily or sugary leftovers: sauces and mixed ingredients make intake and spoilage difficult to control.
• Wet meat, dairy or moist pet food: mealworms are not strictly vegetarian, but these foods spoil quickly and are unnecessary in a simple home tray.
• Water bowls, soaked bedding and damp sponges: these make excess moisture harder to manage.
• Produce exposed to pesticides or household chemicals: if its history is uncertain, do not put it into a feeder colony.
• Plastic or cardboard as feed: the ability of mealworms to consume some materials in laboratory studies does not make them suitable nutrition.

Research into polystyrene biodegradation is real, but mealworms maintained only on polystyrene showed impaired growth in a controlled study. That research is about waste processing, not a feeding recommendation for insects destined for pets. (4)

How Diet Affects Mealworm Growth and Nutrition

Feed type can change survival, development, reproduction and larval composition. It is not accurate to say that the food makes little difference as long as broad nutritional needs are met. The complication is that no single label, including “high protein,” predicts performance on its own.

In the 44-feed comparison, starchy materials generally supported reproduction and larval development better than the legumes tested. The nutrient composition of larvae also differed among feeds, although the relationship was not simple. Substrate protein showed only a weak correlation with larval protein, and protein level did not reliably predict growth or feed conversion. (2)

This is why changing a colony diet should be a measured experiment. Keep the tray conditions stable, introduce one clean ingredient at a time and watch consumption, deaths, growth, odor and moisture. A combination that works in an industrial trial may behave differently in a shallow home container.

Can You Feed Mealworms Kitchen Scraps?

Some unseasoned fruit and vegetable trimmings can serve as moisture food. They should be fresh enough that you would still regard them as sound produce, washed when appropriate and cut into small portions. A bruised carrot end is one thing. A mixed plate of cooked leftovers is another.

Food-waste research also needs context. One 2024 study found that cucumber or tomato waste added to wheat bran improved growth and changed aspects of larval composition. The larvae were reared under controlled conditions, and each experimental diet used a defined 1:1 feed ratio over six weeks. That result does not mean any household waste, in any quantity, will have the same effect. (3)

What Do Mealworm Beetles Eat?

Adult darkling beetles can use the same basic dry food and moisture sources as the larvae. Keep the breeding substrate dry, make moisture food easy to remove and do not bury wet produce. Pupae are different: they do not feed at all.

Knowing which stage is in the tray prevents two common mistakes, feeding inactive pupae and discarding substrate before tiny larvae appear. Our mealworm lifecycle and growth guide explains eggs, larvae, pupae and beetles in detail.

Gut Loading vs Everyday Colony Feeding

These terms are often blended together, but they describe different jobs. Everyday feeding keeps the colony alive and growing. Gut loading is a short, deliberate feeding period before the insects are offered to an animal. Dusting happens after the mealworms leave the colony.

A controlled study using one specific commercial high-calcium gut-loading diet found that mealworm calcium increased after 24 hours and remained elevated at 48 hours. It did not establish that bran, carrots or a homemade calcium mixture will produce the same result. Follow the directions for the gut-loading product and the feeding plan appropriate to the animal. (5)

Feeding Mealworms to Pets

A well-run colony gives you control over feed, moisture, feeder size and harvest timing. It does not make mealworms a complete diet for every pet. Serving size, frequency, supplementation and whether live prey is appropriate depend on the species, age, health and rest of the animal's diet.

Mealworms are naturally calcium-poor relative to phosphorus. The MSD Veterinary Manual lists a calcium-to-phosphorus ratio of about 0.11 for mealworms in one feeder-insect comparison, which is why reptile guidance often includes a species-appropriate supplementation plan rather than relying on mealworms alone. (6) Our guide to mealworms for lizards and other reptiles covers feeder size, variety, gut loading and dusting in more detail.

For poultry, mealworms are normally an addition to a complete ration, not a replacement for it. See our article on feeding mealworms to poultry and Hatching Time's broader chicken treats guide before deciding how they fit into the flock's diet.

If you are comparing mealworms with other protein sources, use our mealworm nutrition comparison as context, then follow guidance written for the animal you actually feed.

How Diet Changes Mealworm Frass

As larvae eat, they leave behind frass, shed skins and fine feed particles. The input diet affects what that material contains, so frass from different colonies should not be treated as a standardized fertilizer with one guaranteed analysis.

Research has examined mealworm frass as a potential biofertilizer and plant-stress treatment, with results that changed according to the insects' diet and the way the frass was used. That supports the original point that feed matters to the output. It does not support the old three-diet table in this article, whose percentages were internally inconsistent, or a promise that every batch will have the same nitrogen or plant-defense effect. (7)

Frequently Asked Questions

Can mealworms eat apples?

Yes. A small piece of apple can provide moisture, but it softens and molds faster than carrot or potato in many trays. Place it on the surface, check it daily and remove it before it spoils.

Can mealworms eat bananas and banana peels?

Mealworms can consume banana, but ripe fruit is wet and sugary. Use a small piece rather than covering the tray, and remove uneaten material promptly. If using peel, wash it and avoid produce with uncertain pesticide exposure.

Can mealworms eat bread?

They can eat plain, dry bread, but it is not a better base than clean bran or another suitable grain feed. Avoid moist, moldy, buttered, salted or flavored bread. If the goal is a stable colony, a consistent dry substrate is easier to manage.

Can mealworms eat oats or oatmeal?

Plain dry rolled oats and oat bran are commonly used. Do not add cooked oatmeal because the added moisture turns the substrate sticky and increases spoilage risk. One study's result for oat flour should not be generalized to every form of oats.

Can mealworms eat meat?

Mealworms are capable of consuming some animal-derived material, so calling them strict vegetarians is inaccurate. In a home feeder colony, wet meat and moist pet food are poor routine choices because they spoil quickly and make hygiene harder to control. A grain base with managed produce is simpler and safer.

Do mealworms need water?

They need moisture, but not an open water dish. Give a small piece of firm produce and keep the grain substrate dry. Replace moisture food as needed, and remove it at the first sign of spoilage.

What do mealworm beetles eat?

Adult darkling beetles can eat the same dry grain base and moisture foods used for the larvae. Pupae do not eat. Separate life stages according to the breeding system so food and cleaning do not disturb eggs or pupae.

Can dogs eat mealworms?

Do not assume that live mealworms from a home colony are an appropriate dog treat. A dog's needs are different from those of an insect-eating reptile or bird, and any insect-based food should be formulated or selected for dogs. If you are evaluating a treat, review the ingredients, processing, texture and portion size. Oldfield Pets' guide to choosing natural treats and chews for pets explains those checks. Ask a veterinarian about an individual dog's diet or allergy concerns.

Mealworm Feeding Checklist

• Use a clean, dry grain-based food such as wheat bran as the main substrate.
• Keep dry food available and top it up according to consumption.
• Offer small pieces of firm produce for moisture and check them daily.
• Remove wet, moldy, buried or bad-smelling material immediately.
• Treat colony feeding, gut loading and dusting as separate processes.
• Match feeder size, frequency and supplements to the animal, not to the size of the colony.
• Record diet changes so you can connect growth or hygiene problems with what changed.

References

1. Morales-Ramos et al. Rearing Methods of Four Insect Species Intended as Feed, Food, and Food Ingredients: A Review. Journal of Economic Entomology.
2. Rumbos et al. Evaluation of Various Commodities for the Development of the Yellow Mealworm, Tenebrio molitor. Scientific Reports.
3. López-Gámez et al. Improving Tenebrio molitor Growth and Nutritional Value through Vegetable Waste Supplementation. Foods.
4. Wang and Tang. Effects of Polystyrene Diet on the Growth and Development of Tenebrio molitor. Toxics.
5. Boykin et al. Using a Commercial Gut-Loading Diet to Create a Positive Calcium-to-Phosphorus Ratio in Mealworms. Journal of Herpetological Medicine and Surgery.
6. MSD Veterinary Manual. Nutrition in Reptiles.
7. Poveda et al. Mealworm Frass as a Potential Biofertilizer and Abiotic Stress Tolerance-Inductor in Plants. Applied Soil Ecology.