Your pool is likely to get invaded by a number of bugs and insects during the warmer months of the year. One of the more common sights may be a tiny black bug with apparent wings swimming around your pool water. The most likely candidate for the swimming pest is a whirligig beetle.
Whirligig beetles can span anywhere from 1/8 inch to 1-3/8 inch long. The beetles have the classic, oblong body shape known to many other species. They are jet, glossy black in color, with two distinct wings on their backs. The pests swim in jagged, jerky motions that appear erratic to the general observer.
The whirligig beetles have mouth parts designed for chewing. They either skim along the bottom of the pool and eat organic matter, or feed off tiny organisms at the surface, mostly other insects. The whirligig larvae eat microscopic organisms, but eggs are typically laid on plants, so you probably do not need to worry about larvae in your pool.
Whirligig beetles are known for forming large clusters, which can be quite a burden for the pool keeper. The gathering behavior could possibly be to help deter potential predators. They will emit a foul odor when threatened, as well as a milky white substance. Their wings allow them to fly away from predators and seek out other bodies of water.
The easiest way to remove whirligigs from pools is with a dip net. Simply scoop the beetles out in clusters and scoop them into plastic trash bags. Make sure to take the bag far away from your home for disposal. Prevent beetles by turning off lights at night. The beetles are attracted to light, so pool lights could be a beacon to stray whirligigs.
There are other possibilities as to what tiny black bugs are plaguing your pool, all with similar removal and prevention methods. Other potential pests include predacious divining beetles, backswimmers or possibly stoneflies.