Feasting Flatworms: How Do Environmental Factors Impact Planaria?

Overview

This project studied food intake levels of planaria experiencing different environments. The dependent variable was the area of the gastrovascular cavity in proportion to the area of the planarian after eating. Two different independent variables were tested to develop a broader understanding of how environments impact planaria: (1) light wavelength. The hypothesis was that planaria in low light environments would eat the most, followed by red light, due to it being less stimulating, followed by green light, which is usually the most stimulating. (2) population density. The hypothesis was that planaria in low population density environments would eat more than planaria in high population density environments. In the experiment, 56 planaria were exposed to 5 environments (control, red light, green light, overpopulated, underpopulated). After four days, the feeding was conducted using red-dyed organic ground beef. After 1 hour, three planaria per group were photographed. The photos were uploaded into an image analysis software, and the proportion of the gastrovascular cavity was calculated. For light wavelength, the red light group averaged 67.0%, the green group averaged 72.5%, and the control group averaged 61.3%. Therefore, the planaria in the green light group ate the most, contradicting the hypothesis. This may be because of nocturnal adaptation. The planaria likely felt less stimulated in light with longer wavelengths (red) because it penetrates the least through water. However, the wide range of green light results decreased confidence in this finding. For population density, the underpopulated group averaged 72.8%, the control group averaged 61.3%, and the overpopulated group averaged 58.7%. Therefore, the underpopulated group ate the most, supporting the hypothesis for this project. The tight range of results added confidence to this data. Based on the results and further research, competition for space decreased activity level and, therefore, decreased food intake. In the real world, these results might imply that population density is important for animal comfort, food intake, and potentially overall well-being.

Competition history

• CSEF 2026 Zoology (Junior Division) · Entry J-20-08

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