Mealworms, the larval stage of the darkling beetle (Tenebrio molitor), are a popular and nutritious food source for various animals, including birds, reptiles, fish, and even some small mammals. Raising mealworms is a relatively straightforward process, making it an attractive option for pet owners, breeders, and even those interested in sustainable food sources. This article provides a comprehensive guide to mealworm beetle diet and care, covering everything from setting up a colony to troubleshooting common issues.
Understanding the Mealworm Life Cycle
Tenebrio molitor undergoes complete metamorphosis, with four distinct life stages: egg, larva (mealworm), pupa, and beetle. The duration of each stage is influenced by factors such as temperature, humidity, and food availability.
- Egg: Female beetles lay approximately 275 tiny, white, bean-shaped eggs over two to three months. These eggs are sticky and quickly become coated in the substrate, making them difficult to spot. The eggs typically hatch in 4-19 days, usually 4-7.
- Larva (Mealworm): The larval stage lasts for about 10 weeks. During this period, the mealworms actively feed and grow, molting their exoskeletons as they increase in size.
- Pupa: The larvae then transform into pupae, which resemble alien grubs. The pupae don't eat or move much. This stage lasts for 6 - 18 days (7-24 days or more).
- Beetle: After pupation, the adult beetles emerge. Initially, they are white/light beige with a soft shell, gradually darkening to red, brown, and finally dark brown/black after 2-7 days. The beetles cannot fly, but they can move quickly. They lay eggs 9 - 20 days after emergence and continue laying for two or three months before dying.
Setting Up Your Mealworm Colony
Container Selection
The choice of container is crucial for a successful mealworm colony. Consider the following factors:
- Material: Opt for glass, metal, or plastic containers. Avoid cardboard or fabric-lined containers, as mealworms can easily escape from these. You want to be sure they can’t get a grip on the sides of the container you keep them in, as they could likely climb out.
- Size: A shoe box-sized or sweater storage container is generally sufficient for a small colony. For larger-scale production, consider using a four-drawer container or a 64-quart Rubbermaid container, which can hold 50,000 to 100,000 larvae. Mealworms may thrive more in a container with a large surface area. A larger surface area may improve survival by dissipating heat.
- Depth: Ensure the container is at least 1 inch deep to prevent the larvae from escaping. As long as the larvae are 1″ or more below the top of the container, they can’t get out.
- Ventilation: Adequate ventilation is essential to prevent mold growth. If using a plastic cover, drill holes in it. Some commercial farmers do not cover their bins.
- Cover: While darkling beetles can't fly, a cover is recommended to keep out mice, rats, cockroaches, and spiders, which may prey on mealworms.
Substrate and Bedding
The substrate serves as both food and bedding for the mealworms. Commonly used options include:
- Wheat bran: This is a popular and readily available choice. Use it in 1.5-2″ deep layers.
- Rolled oats (oatmeal): Uncooked, old-fashioned oats are preferable to instant varieties.
- Chick starter/mash: This is a nutritious option available from feed stores. Ensure it is non-medicated.
- Cornmeal: Fine particles make it easier to sift out large mealworms.
You can also supplement the substrate with other food sources, such as:
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- Ground dry dog or cat food
- Ground eggshells or cuttlebone (for calcium)
- Soybean meal
- Wombaroo insectivore mix
- Fish flakes
- Fine mouse cubes
- Bone meal
- Graham (whole wheat) flour
- Dry brewer's yeast
Layer the food/substrate/bedding in 2-3″ inches deep. Replenish the food often, as the worms eat a lot. Change the food out about once a month. Feed the beetles too (same stuff). Fine particles (fine wheat bran, corn meal, chick starter) make it easier to sift out large mealworms. Larger particles (e.g., rolled oats) with larger worms make it easier to sift out frass so you don’t waste food.
Maintaining Optimal Conditions
- Temperature: Mealworms thrive at temperatures between 75-81°F (24-27°C). Temperatures below 62ºF may halt reproduction. Consistent with the name darkling beetle, they prefer the dark. Keep the container out of direct sunlight.
- Moisture and Humidity: Mealworms require moisture for growth and reproduction. Beetles lay more eggs when the relative humidity is higher - ideally 70% (55-80% is good).
- Providing Moisture: Add chunks of cabbage, raw potato, a slice of bread, romaine lettuce, kale, yam, or apple slices to the container. Other options include celery, broccoli stems, carrots, banana peels, or asparagus chunks. Cover cabbage etc., with a cloth to keep it from drying out if you use a heat lamp. A crust of bread can also be laid face down on the bedding. Place potato/apple slices cut side up, even with top of bedding.
- Maintaining Humidity: Place a small bowl filled with water in the middle of the farm to increase relative humidity. A sponge can be placed in the bowl to increase the moist surface area. Emad uses a moist sponge wired to the container lid. You can also put the bottom of the sponge in a plastic baggie (to prevent the meal from getting wet and moldy) and stand it upright in the corn or oatmeal.
- Avoiding Excess Moisture: More is not better. If you put too much in, or leave it too long, it will get moldy or become a gooey mess.
Feeding Your Mealworms
Mealworms are not picky eaters and will consume a variety of organic materials. A balanced diet is essential for their growth and nutritional value.
- Staple Foods: Wheat bran, rolled oats, and cornmeal form the basis of their diet.
- Moisture Sources: Fruits and vegetables provide essential moisture. Good options include potatoes, carrots, apples, cabbage, and lettuce.
- Supplements: You can sprinkle the vegetables/fruit with calcium and vitamin supplements to add nutritional value. Experiments where skim milk (calcium source) was added to wheat bran (1:3 or 1:2 ratio) yielded better growth than wheat bran alone.
To give your mealworms water, add moist foods to their container, like pieces of fruit or vegetables. Make sure you give your mealworms new food and water whenever they're running low. Give the mealworms a variety of different foods 24 hours before you feed them to your pet. Feeding them potatoes, apples, carrots, etc.
Colony Maintenance and Cleaning
Regular maintenance is crucial for a healthy and productive mealworm colony.
- Removing Debris: Remove dead mealworms, beetles, and pupae regularly to prevent mold infestations. Dead larvae turn black. Dead pupae turn brown and shrivel up. Deformed beetles die early.
- Sifting Frass: As the mealworms consume the bran, a fine, dusty residue (frass) will accumulate at the bottom of the container. Eventually, shed exoskeletons and waste products (frass) will build up, and a slight ammonia odor may be detected. Sift the grain to separate the worms and adult beetles. The frass (waste) can be used as fertilizer for flowers or vegetables. Frass should be removed as required, usually every 3-4 weeks. You can get a variety of sieves with different mesh sizes to filter out different fractions of the frass. For instance a larger mesh size will filter out beetles and pupa but leave substrate and eggs behind. A smaller mesh will separate out mealworms/meal and remove frass.
- Cleaning the Container: Wash the container with soap and hot water or natural disinfectant when replacing the bedding. Clean the old container with soap and hot water or natural disinfectant.
Sifting Techniques
- Manual Sifting: You can make a sifter with #8 (1/8″) hardware cloth or nylon reinforced screen tacked onto a wooden frame. If a sifter is made to fit in the bottom of the mealworm container, the frass will fall through the sifter, making it easier to clean the container.
- Separating Stages: If you do not separate them, do not change the bedding after the worms turn into beetles, as it contains eggs of future worms. You really should go through the entire farm about 3 times a year to separate out the beetles into their own container and add fresh bran. Others farmers separate them out, since larvae and beetles might chow on the inert pupal stage, and beetles may eat pupa/eggs. o separate the beetles out, you can catch the live ones easily by providing apple slices. They swarm to the apple - just lift it and shake off swarm after swarm.
Managing Different Life Stages
Some breeders prefer to keep the different life stages separate to optimize production and prevent cannibalism. Here are a few methods for separating mealworms, pupae and beetles:
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- Multi-Container System: The best set up may be to have two containers that fit inside one another. Put the beetles in Container A, and put small holes (smaller than beetles, bigger than bran) or screen the bottom of that container. Sit Container A inside Container B. Every 2 days to 2 weeks, shake out the bran (with eggs) out of Container A into Container B. The beetles stay behind. Add more food and moisture sources as necessary to A as necessary. Once you’ve collected enough bran and eggs in the B, transfer the contents to a “nursery” container (Container C) with a source of moisture and let it sit for 30-40 days, and start over again. You can cover Container C bedding with a piece of newspaper or cloth that is spritzed lightly with water on a daily basis. Container A can be a big Rubbermaid bin with a lid. Containers B and C can be open shoe box size containers that sit inside of Container A. Let adults emerge before disturbing. Pick out the beetles out of Container B every couple of days (you can use a spoon) and put them in Container C with some bran and folded cloth they can lay eggs on. After 2-8 weeks, take the beetles out of Container C and feed them to the birds/discard. Let the eggs in Container C hatch. For the first couple of weeks/months you can hardly see the larvae. Tens of thousands fit in a shoe box size container.
- Pupae Separation: If you plan to keep your mealworms and let them develop into pupae and eventually beetles, make sure to take the pupae out of the container. If you notice pupae in your container, transfer them into another container that is lined with a paper towel rather than the bedding.
Troubleshooting Common Problems
- Mold Growth: Ensure adequate ventilation and avoid overwatering. Replace moist food regularly and consider using a dehumidifier if necessary. Mealworms do need some humidity, but when it gets too humid, fungi propagate really rapidly. These fungi can actually attack the mealworms themselves and kill them. As you start having dead mealworms mixed in with the oatmeal, it just creates exponential growth of that fungus in the enclosure. If you have a way of measuring the humidity itself, that will help you a lot. There are multiple kinds of humidity meters that are very easy to procure. Most of them measure both humidity and temperature. If your colony has a bad fermenting or ammonia smell, it is likely the frass has gone moldy and needs replacing.
- Slow Growth: Check the temperature and humidity levels. Ensure the mealworms have access to a nutritious diet.
- Cannibalism: Provide adequate moisture and food to prevent mealworms from eating each other.
- Pests: A variety of methods are employed to prevent and remove pests from mealworm farms.
Harvesting and Storing Mealworms
- Harvesting: Mealworms are typically harvested when they reach their desired size, usually after 8-10 weeks.
- Storage: Worms that you don’t want to reproduce can be kept in a closed container (with holes drilled in it) in the refrigerator. Lay a paper towel on top to prevent condensation. At 38ºF, or even 45-50ºF they will last along time (months) in a semi-dormant mode. One source says larvae can stay alive 80 days at 23ºF. They will not pupate in the refrigerator.
Preparing Mealworms for Consumption
- Gut Loading: Some people do “gut loading” (offering extra food or protein to the mealworms) two days before feeding to animals.
- Dusting: You can “dust” the outer part of mealworms with powdered mineral or vitamin formulations (e.g., Powdered Calcium [Ca2+] or calcium-vitamin combinations) prior to feeding it to an animal. Put larvae or beetles in a baggie, and gently shake them to coat them with the mineral-vitamin powder.
Uses for Mealworms
- Animal Feed: Mealworms are a nutritious food source for various animals, including:
- Birds: Bluebirds relish mealworms. Includes many songbirds and chickens, turkeys, guinea fowl, peafowl, quail, chukar, pheasant, and domestic ducks. Small birds like finches prefer 0.5″ size (worms 4-6 weeks old).
- Reptiles: Aquatic turtles of all sorts, box turtles, tortoises), reptiles (sailfin lizards, chameleons, fringe-toed lizards, basilisks, water dragons, basilisks, anoles.
- Fish: Excellent fish bait. Mealworms last on the hook longer than many other kinds of live bait. Tropical fish.
- Amphibians: Frogs (e.g., dart), toads, salamanders and newts.
- Small mammals: Small mammals, e.g.
- Human Consumption: Yes some people actually eat them. Freeze for 48 hours first. They will keep in the freezer for a few months if they are properly wr..
- Other uses: You might consider selling excess worms to a local pet store or a zoo.
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