Flying crab is a kind of marine life, which mainly lives in shallow water. As far as I know, flying crabs are usually active on sunny days. Sunny sunshine can provide enough light and temperature, which is very important for the growth and reproduction of flying crabs. In addition, sunny weather can raise the water temperature on the ocean surface, which is also helpful for the activities of flying crabs. On the contrary, there is less light on cloudy days, and the seawater temperature will be lower, which may reduce the activity of flying crabs. Therefore, flying crabs have more opportunities to be active in sunny days. However, please note that it is not accurate to predict the activity of flying crabs only based on the weather, because their activities will be affected by other factors, such as seasonal changes and tides.