The low mass of a mosquito allows it to fly in the rain. The weight of a raindrop is much greater than the weight of a mosquito, so even a light rain can potentially knock a mosquito out of the sky. However, the mosquito's low mass means that it has a high surface area to weight ratio. This means that the mosquito can generate a lot of lift with its wings, even in the face of strong winds and heavy rain.

In addition, the mosquito's body shape is also designed for flying in the rain. The mosquito's body is long and thin, with a small head and a large thorax. This design makes the mosquito more aerodynamic, allowing it to fly more easily through the rain.

Finally, the mosquito's wings are covered in tiny hairs that help to repel water. This means that the mosquito's wings do not get wet easily, which allows the mosquito to fly even in the heaviest of rain.

As a result of these factors, mosquitoes are able to fly in the rain even though they are very small and lightweight.