Planaria make an excellent subject for animal behavior observation since they are small and inexpensive. They need to be viewed under a microscope or stereoscopic microscope, so they also provide students with an opportunity to practice their lab techniques and skills. For younger students, a simple lab would give them the opportunity to observe the planaria under the microscope, note their behavior and draw their external anatomy. Students should note how the planaria move, what and how they eat and how they interact with other organisms in the environment. Students can do independent research on planaria before they observe them and note behavior that confirms or contradicts the information they've gathered. Older students can experiment with behaviors like kinesis and taxis by introducing and removing stimulants like light, chemicals, touch and orientation and observing how the planaria react.
Planaria, like earthworms, have the uncommon ability to regenerate when they are cut or damaged. Students can cut the planaria in a variety of ways and predict what the regenerative results will be, observe and report the final results. This lab is better for older students as it requires the use of a scalpel and observation over a period of time as the planaria regenerate. For students learning about complex and difficult-to-observe concepts like stem cells, this is a wonderful opportunity for them to observe regenerative ability in action.
With concerns over infiltration of pesticides and other toxins into the world's water systems growing, it is particularly timely to use planaria to teach students about the effects of these chemicals on aquatic ecosystems. Planaria should be separated and different types and concentrations of chemicals added to the water. Students can observe any changes in behavior, ill effects or deaths resulting from toxic exposure. Students should also be aware that planaria locate food by sensing the chemicals in food with chemoreceptors on their bodies. These receptors may affect whether they are drawn to the chemical initially by mistakenly believing it is food. All observations should be recorded. Students can report on whether or not chemicals commonly introduced into water systems by humans have an observable negative impact on planaria.
Planaria make interesting subjects for a lab on reproduction because they are capable of both sexual and asexual reproduction. They are also hermaphrodites, so each planaria give sperm to its partner during fertilization in the hopes that both partners will be impregnated. For asexual reproduction, a planarian will "drop" or shed its tail and each half will regrow into a complete independent planarian. For this lab, students can observe planaria mating, or encourage asexual reproduction by cutting the planaria in half with a scalpel. They can hypothesize whether sexual or asexual reproduction would be the preferred method for breeding, and why and whether certain stresses or environmental changes cause the planaria to favor one method over the other.