Leaf slug's have one key plant-like characteristic: They can perform the process of photosynthesis, which is the process by which plants can use sunlight to create energy from carbon dioxide and water. How do they do this? Their primary diet is sea algae. When they consume it, they suck the chloroplasts out of the algae in a process called kleptoplasty. This process then enables them to photosynthesize. This is why leaf slugs glow, In other words, they are bioluminescent.