What are the little black things that swim in your pool and then fly away?

There are several types of insects that can be found in swimming pools that fit this description. Here are a few possibilities:

1. Springtails: Springtails are small, wingless insects that are commonly found in moist environments, including swimming pools. They are typically dark in color and have a distinctive "spring" or tail-like appendage on their abdomens, which they use to jump. Springtails are harmless to humans and do not pose any health risks.

2. Water Boatmen: Water boatmen are small, aquatic insects that are often seen swimming on the surface of the water in pools. They are dark brown or black in color and have long, oar-like hind legs that they use for swimming. Water boatmen are not harmful to humans and are actually beneficial, as they help to control mosquito populations by feeding on mosquito larvae.

3. Diving Beetles: Diving beetles are larger, aquatic insects that are also sometimes found in swimming pools. They are dark brown or black in color and have a streamlined body that allows them to swim quickly through the water. Diving beetles are predators and feed on other aquatic insects, such as mosquito larvae. They are not harmful to humans.

4. Water Striders: Water striders are small, long-legged insects that are often seen skating across the surface of the water in pools. They are dark brown or black in color and have long, slender legs that help them to distribute their weight and stay afloat. Water striders are not harmful to humans and do not pose any health risks.

It's important to note that there are other types of insects and bugs that can be found in swimming pools as well, but these are some of the most common ones that fit the description of being small, black, and able to swim and fly.