Rearing Mealworms

Rearing Mealworms

David Shetlar & Matthew Volkman

Department of Entomology

Mealworms are the juvenile stage of the darkling beetle, Tenebrio molitor, and have been used in a wide variety of ways by humans for many years, largely due to the fact that they are so easy to rear.  Biology laboratories will often use mealworms for conducting experiments, people use them as bait for fishing, and food for a wide range of insect-eating pets including small mammals, birds, reptiles, and fish.  Other parts of the world use mealworms as a protein source in their own diets, and in recent years a growing number of people in the United States have turned to mealworms for protein as well.

Identification

The four life stages of mealworms are egg, larva (mealworm), pupa, and adult (beetle).  Eggs are white, bean shaped and about 1/120 inches long. Larvae are white immediately after shedding their skin, and darken to a shiny honey-yellow, and darken slightly before molting again. The mealworms will molt 9-20 times before reaching adulthood in approximately six months at 80˚F, and will reach about 1-1/4 inches in length.  The pupae start as white and turn a pale yellow. Newly emerged beetles are a red-brown color but they soon turn a dark brown to black color.

Color change of the beetle from first emerging to fully darkened. Credit: Matt Volkman

Setting Up Your Container

Depending on your intended use of the mealworms, and the amount of work you are willing to spend, there are two main set-ups.  In a single container system, all life stages to coexist together, and the population is continuously renewing itself.  The other set-up calls for keeping life stages separate, and is more conducive to producing larger amounts of mealworms.

Single container system:  (Picture of container needed)

Benefits Drawbacks
Less time consuming Slower population growth
Less space consuming Cannibalism of pupae

Start with a plastic container whose dimensions are anywhere between the size of a shoe box and dresser drawer.  The walls should be at least 4 inches tall.  Next, add the bedding material to the bottom of the container, starting with wheat bran from ½ to one inch in depth, then add rolled oats or chicken mash to the top of the wheat bran for an additional ¼ to ½ inch.

At this point add in 300 to 500 mealworms as well as a slice of apple, a slice of potato, or a few pieces of carrot as a water source.  Cover the bedding/mealworms/carrots mixture with strips of newspaper, sprinkling the newspaper every other day with a little bit of water so that it is slightly damp.  Remove the used apple, potato, of carrots and replace them once per week.Start with a plastic container with a lid whose dimensions are anywhere between the size of a shoe box and dresser drawer.  The walls should be at least 4 inches tall.  Next, add the bedding material to the bottom of the container, starting with wheat bran from ½ to one inch in depth, then add rolled oats or chicken mash to the top of the wheat bran for an additional ¼ to ½ inch.

A screen lid can be fashioned by cutting the middle of the original lid out and hot gluing screen over the hole.  This will allow for airflow, while keeping all of your mealworms and beetles contained.

The ideal environmental conditions for the container are 25˚C and 70% relative humidity.

Multiple Container System:

Benefits Drawbacks
Pupae safe from cannibalism Requires more attention
Population can grow faster More containers
Easier to track life cycle

For this system, you will need two of the previously discussed containers, one for growing the mealworm larvae, and one for breeding the adult beetles.  A third container will be needed for allowing the pupae to pupate into adults away from the mealworms and beetles.  This keeps them safe from cannibalism by the beetles and mealworms.

Separate container system. Left to right we see mealworms, pupae, and beetles.  Credit: Matt Volkman

The mealworms will develop in their own container, and when you see pupae beginning to form in a container, you will have to move them to the pupation container.  You will want to check the mealworm containers on a regular basis, anywhere from once per day to once per week.  Once the pupae become adults, you will want to move them into a breeding container, and periodically check the pupae container for beetles as well.

Additional Note:

Additional food is added from time to time, and it is usually necessary to clean out the container completely at intervals of 3-6 months, removing waste, molted skins, and dead insects.

Obtaining Your Mealworms

Mealworms can be purchased easily and at a low cost.  Some live bait shops will have smaller amounts, 50-300 mealworms per container, pet stores may have somewhat larger amounts, up to 1000 mealworms per container, and there are a multitude of internet stores offering a variety of live mealworms.  You can purchase mealworms at several different sizes and quantities.  A mealworm population can be started by introducing 500-1000 mealworms into one or a few containers at once.

CAUTION! – If you don’t have a local pet store where you can obtain mealworms, be sure that you follow a few guidelines when ordering mealworms online. Check customer reviews; order the mealworms during moderate weather as the package can be exposed to freezing temperatures or extreme heat; use rapid shipping; and, don’t hesitate to contact the supplier to establish a relationship.

Feeding Your Mealworms

Mealworms are a natural pest of grains, so they will readily feed on the wheat bran and rolled oats used for the bedding.  As discussed previously, a half inch to an inch layer of these grains serve as food and hiding places for the eggs, larvae, pupae and adults. Mealworms are able to absorb water from the air through their skin and they make metabolic water as they digest their food, but mealworms do much better if supplied a water source.  Some common water sources used are carrots, apples, and potatoes.  Other vegetables may be used, but it is important to keep an eye on the wet foods so they do not begin to mold and ruin your bedding.

Below we see a few videos which have been sped up, of mealworms and beetles in an all oats bedding being fed carrots as their water source.  Videos are courtesy of Matt Volkman.

References

Martin R. D., J. P. W. Rivers, and U. M. Cowgill. 1976. Culturing mealworms as food for animals in captivity. Principles of Zoo Animal Feeding. 63-70.