Mealworms are the larval stage of the darkling beetle (Tenebrio molitor). They are known for their high nutritional value and are a common food source for pets and humans. A common and concerning question for those raising them is whether they consume each other. The answer is yes; they will engage in cannibalism under certain conditions. This behavior is not a primary feeding strategy but a survival response, often triggered by insufficient resources or the presence of vulnerable individuals in their environment. Understanding the circumstances that lead to this predatory action is necessary for maintaining a healthy and productive colony.
When Mealworms Engage in Cannibalism
Mealworms primarily target the most defenseless life stages within their own population. The most common victims of cannibalism are the pupae, which are soft-bodied and immobile as they undergo metamorphosis into adult beetles. Larvae and adult beetles readily prey upon pupae because their lack of mobility makes them an easy source of nutrients and protein.
Newly molted larvae are also highly susceptible to attack. Their exoskeleton is soft and white before it has a chance to harden, a process known as sclerotization. Larvae typically shed their skin multiple times to accommodate growth, making them vulnerable immediately following each molt. Larvae and adult beetles will also consume injured, weakened, or dead individuals in a form of necrophagy, which helps keep the colony clean.
Environmental Triggers for Self-Consumption
The primary drivers of cannibalism in mealworm colonies are environmental stressors that signal a lack of necessary resources.
Moisture Deficiency
One of the strongest triggers is a deficiency in moisture. Mealworms primarily obtain water from their food source, so a lack of fresh produce or other moisture-rich supplements prompts the insects to seek fluids from their conspecifics. This deficiency leads to higher rates of attack on other life stages, as the mealworms attempt to hydrate themselves.
Insufficient Protein
The composition of the diet, particularly the protein content, also plays a significant role in triggering cannibalism. Wheat bran, a common staple, often contains only 13–18% protein. This is lower than the approximately 20% protein mealworms will naturally select for optimal growth. When the diet is insufficient, larvae may resort to consuming their peers to fulfill this specific nutritional requirement.
Overcrowding and Starvation
High population density and starvation are additional factors that increase the likelihood of cannibalistic behavior. When too many individuals are confined to a small space, the stress and competition for food and space can lead to aggression and the consumption of eggs or pupae. Studies show that even a starvation period of more than 12 hours can significantly increase the rate of cannibalism.
Maintaining Conditions to Discourage Cannibalism
Preventing cannibalism involves directly addressing the environmental deficiencies that trigger the behavior.
Hydration and Diet
Providing an adequate source of hydration is paramount. This is often achieved by regularly supplying fresh vegetables like carrots, potatoes, or apples. These produce items serve as the primary water source for the colony, reducing the motivation to seek moisture from other mealworms. A high-protein diet is also necessary to discourage the larvae from seeking protein from their own kind. Supplementing the wheat bran substrate with protein-rich ingredients, such as nutritional yeast or specialized insect chow, can significantly reduce the cannibalism rate. Ensuring the diet contains at least 20% protein is an effective strategy for improving survival and growth.
Population Management
Managing the population density and isolating vulnerable life stages are practical measures for reducing cannibalism. Separating the immobile pupae from the highly active and hungry larvae and adult beetles will immediately protect them from attack. Using larger containers or routinely sieving the substrate to separate different sizes of larvae also helps to minimize the stress of overcrowding and competition for resources.