1 class periods of 45 minutes each
The mealworm is the larval stage of the darkling beetle. The darkling beetle undergoes complete metamorphosis. Students each receive a mealworm to place in a habitat and take back to their classroom. They make observations of their mealworm and watch as it progresses from the larva to the pupa and finally the beetle will emerge. Students will then release their darkling beetles outside.
The mealworm is NOT a worm. It is the larval stage (grub) of the yellow mealworm beetle, also called the darkling beetle (Tenebrio molitor). Although the grub looks a bit like a worm, the mealworm has six small, jointed legs.
The mealworm undergoes complete metamorphosis. The female darkling beetle lays hundreds of tiny, white, oval eggs, which hatch into tiny mealworms (the larval stage) - it takes from 4 to 19 days to hatch. Each mealworm eats a tremendous amount and grows a lot, molting (shedding its exoskeleton) many times as it grows. It then enters the pupal stage (this stage lasts from 2-3 weeks, up to 9 months, if the pupal stage over-winters). The pupa does not eat and seems inactive, but it is transforming itself into an adult. After pupating, a white adult darkling beetle emerges from the pupa -- it soon turns brown and then almost black. The adult lives for a few months.
Both the adults and the larvae are scavengers that eat grains and some seedlings. Because of this, it is considered a pest. They also eat decaying material, like decomposing animals and dead plants. They get all the water they need from the food they eat. Mealworms are eaten by many animals, including many birds, rodents, spiders, lizards, and some other beetles.
Preparation: Mealworms should be purchased two to four weeks before the class date. This will reduce the time the mealworms will be in the classroom because they are growing and eating before the students get them. Place the mealworms in a container with wheat bran as the bedding. Add a few teaspons of whole wheat flour. Cut up a potato and place the pieces into the bedding. As the potatoes dry out, add fresh potatoes. With starting 2 to 4 weeks before class you should get a pupa before class time. If you want to start the worms a month before the class you will probably have a beetle before class time.
Tell the students that they are each going to take an animal back to their classroom to take care of over the next several weeks. Ask them what kind of animal they think they will receive. Tell them they are going to be taking care of a mealworm. Explain the mealworm life cycle and that they will be making a habitat for their mealworm. Explain the purpose of the wheatbran for bedding, the whole wheat flour for food, and the potato for moisture. If this is presented with excitement and fascination, these emotions are very contagious to the students. Explain to them that it is a big responsibility to take care of an animal and that they will learn how to do that safely today.
Rio Tinto Hands-on Science Curriculum Team