The Multipurpose Mealworm
You have probably encountered mealworms some time in your life, although you may not have known what they were. Perhaps Grandma had an infestation in the flour in her pantry, or Uncle Joe used them for bait when fishing (see Reference 1). Mealworms are also used for food for pet reptiles (2) and birds (3) and even ant farms. But did you know that they also have potential for science projects? Mealworms are easy to obtain, easy to take care of, don’t take up much space and lend themselves to many simple experiments.
Mealworms get their name from the fact that they feed on flours, such as oat meal, corn meal or wheat products. The mealworm itself is an elongate yellow-brown cylinder with six small legs right behind its head. It is the larval or immature stage of a dark brown to black beetle in the family known as darkling beetles. Three species are available. The most common is the yellow mealworm, Tenebrio molitor. You may also find the dark mealworm, Tenebrio obscurus, or the giant or king mealworm, Zophobas sp. Related species feed in rotting logs or may be agricultural pests by feeding on seedlings. Another genus of darkling beetles (Elodes) is common in the deserts. These beetles stand on their head and spray a chemical at potential enemies.
Where to Get Mealworms
Because they are so nutritious as pet food, most pet stores will probably either have a supply of mealworms or will know where you can find them locally. You may also order from companies such as Rainbow Mealworms (4) or other internet sources, or biological supply companies such as Carolina Biological Supply or Wards.
You may either order as many as you need to complete your experiment, or you may want to try keeping some for a rearing project.
For rearing dark or yellow mealworms you will need a tub or container, some food, a source of moisture and a substrate for the adults to lay eggs. If this is a small project, a clear plastic cup with a cover or a margarine tub will do. Poke small holes in the lid for ventilation with a pin or brad, or remove a quarter-sized hole and cover with screen. Glue the screen in place with a glue gun (5).
Fill the container about one quarter full with wheat bran, crushed wheat cereal, oatmeal, oat bran or corn bran, or a mixture. You can also mix in dry cat food or chicken laying mash, if available. Add a few small slices of apple or potato for moisture. Change the slices regularly. If you notice the flour is molding underneath, lay the slices on a bottle top or other lid. Add a piece of crumbled cork or crumpled paper for the adult beetles to lay their eggs on. Add the larvae and store in a warm (80 degrees F) dark place.
After a few weeks, the larvae should change into something that looks like a soft, immobile beetle. This is the pupal stage. The hard-shelled adult beetle will emerge in 10-20 days. Leave the adults right in the container. They should lay eggs and you will have tiny larvae in a few weeks.
Add more food and remove larvae for experiments as needed. Eventually the mealworms will benefit from a thorough cleaning. Dump the contents into a tray, separate the larvae and pupae from the food, clean the container, add fresh food and return the larvae to their new home. If you don’t like to pick up the worms with your fingers, try a small plastic spoon.
If your pupae start disappearing or have holes in them, the larvae might be feeding on their sisters and brothers. Remove the pupae to a separate container if that’s the case. The bigger king mealworm should probably be raised in individual film canisters because of this problem (2). Also, the king mealworms are sometimes treated with a hormone to prevent them from molting into a pupa. Check with your supplier.
Here are three simple experiments using mealworms. You can probably think of many more.
A. Light versus Darkness
1. To see if mealworm larvae prefer light or dark, collect some clear and black film canisters. Gather some small squares of black paper, some tape, a notebook to write down your results and some mealworms. You may also use a paper cardboard tube with one half of one side cut out and covered with clear plastic to allow light inside.
2. Place a mealworm in a clear film canister. Slide the square of black paper about two-thirds over the opening, to help keep the dark side dark, but with enough room to allow the larva through if it wants to move. Attach the black canister to the other side, place in a well-lit area and record where the larva is every five minutes for 15 to 20 minutes.
3. Repeat with several mealworms. To increase accuracy, place new mealworm in the dark side first. Rotate back and forth. Also use clean film canisters in case the mealworms prefer to go where they smell other mealworms. Or design an experiment to see whether they do prefer the canister that previously held a mealworm. (For other versions of the light versus dark experiment and more information, check references 5,6.)
B. Diet Tests
1. Prepare several similar containers with different foods, such as wheat flour and bran in one cup, corn meal and bran in another, and oatmeal and bran in a third. Give all the cups either potato or apple slices, and keep all other conditions the same.
2. Add the same number of similar-sized larvae to each container.
3. Record either how fast the larvae become adult beetles or how many adult beetles are formed or both to determine which diets perform best.
C. Compare Life Cycles of Species
1. Obtain two or three species of mealworm, and practice rearing them in individual containers such as film canisters (2). When you have adults laying eggs for all species, begin the experiment.
2. Prepare new containers with exactly the same diet and conditions. Add a fresh paper to your rearing container overnight to obtain freshly laid eggs. Cut out the individual eggs and add one to each prepared container. Label the species of mealworm on the container. Set up a similar number, such as ten, for each species.
3. Keep the containers together. Record how fast the larvae emerge, when they pupate and when new adults emerge. Which species has the quickest life cycle? Which is the slowest?
Other experiments include checking to see if adult beetles prefer laying eggs on paper, cloth or cork. Happy beetling!