Author: Jolene Routson
Overview: Students will observe offspring (mealworms) that do not initially resemble their parent organism (darkling beetles) throughout complete metamorphosis. Students will also create and maintain an appropriate habitat for the mealworms.
Grade Span: 35
Mealworms may be purchased in advance and placed in a refrigerator.
Basic discussion regarding inherited traits is suggested.
Time: 5060 minutes for initial observation and set up. Approximately 1015 for daily observations.
Grouping: Solo or pairs
Mealworms are raised commercially as food for many reptiles, amphibians, rodents, birds, and other small animals. The mealworm is actually an insect that undergoes complete metamorphosis. It is not a worm at all. Mealworms are the larvae of darkling beetles. They have four life stages: egg, larva, pupa, adult. Students will be introduced to the mealworm during the larval stage. The larvae are very lethargic and move clumsily. The exoskeletons will be shed (or molted) about five to seven times as they grow.
Under ideal conditions, the larval period lasts about eight to ten weeks. However, it can last several weeks longer at lower temperatures or due to lower food availability. When the larva molts for the last time, a soft new exoskeleton in the shape of a pupa will emerge. The change from larva to pupa is the mealworms first metamorphosis. The pupae move very little and do not eat.
Approximately two to three weeks after pupation, an adult beetle will emerge from the exoskeleton. The adults are whitish after metamorphosis, but soon turn dark brown. Although they do not usually fly, they do crawl almost constantly.
Note: It is not necessary to include water; the mealworm will extract moisture from the fruit. Too much moisture will cause the bran to mold and the mealworms will die. Add a new piece of fleshy fruit or vegetable once a week.
Teacher Resources: Fabulous animal/insect life cycle printouts and quizzes are available through Enchanted Learning at www.enchantedlearning.com/coloring/lifecycles.shtml.
Explore these links for additional information on the topics covered in this lesson:
The key point in this lesson should be that although the mealworm larva initially looked nothing like its parent, it matured to look similar to the parent because of inherited traits. However, unless you have an ongoing mealworm culture, students will not see the parent generation and will have to infer their appearance by looking at the adult forms that result from their mealworms.
Do not create habitats using Styrofoam or cardboard containers because the mealworms can chew through these materials.
Mealworms are available at both pet stores and bait shops. However, if possible obtain worms from a bait shop because they are less likely to be fed hormones that can stop their metamorphosis into beetles.
Vocabulary: metamorphosis, egg, larva, pupa, adult, inherited, traits, exoskeleton
The possibilities for continued experiments are endless. However, some ideas for charts or tables that may be developed are:
- Number of mealworms in each stage of metamorphosis as the weeks progress. This can be depicted in a bar or line graph.
- Record reactions to various stimuli (light, sound, water droplets).
- Record the mass of the potato slice daily. Graph changes.
Further observations and comparisons can be made by observing other insects life cycles. Possible insects include: crickets, grasshoppers, stick insects, fruit flies, and mosquitoes.
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