Spend any time near the water in the summer and there's one thing you're almost sure to see: a dragonfly. The insects are noticeable because of their large size, and they also don't seem to shy away from us. But don't swat at these harmless creatures. They won't sting or bite you, so there's no reason to try to keep them at bay.

The world is home to about 7,000 dragonfly species, and they are usually found near a body of water, according to National Geographic. Dozens of dragonfly species live in Illinois. Many have descriptive names such as little blue dragonlet, cherry-faced meadowhawk, unicorn clubtail and Halloween pennant. 

Dragonflies are important to the ecosystem because they help control insect populations. Since they rely on clean water, they are considered an indicator of a healthy ecosystem, National Geographic reports. 

Read on to learn more about these insects.

Some of them are actually damselflies

Unless you consider yourself an amateur entomologist, there's a good chance that some of the insects you have collectively been referring to as dragonflies are actually damselflies. The two insects are similar, and both belong to the insect order Odonata. Collectively, about 7,000 dragonfly and damselfly species exist in the world, living on every continent except — you guessed it — Antarctica, according to National Geographic.

RELATED: WHAT'S THE DIFFERENCE?: DRAGONFLY VS. DAMSELFLY

So how do you tell the difference between a dragonfly and a damselfly? While they are similar, there are some physical characteristics and behaviors that can help you distinguish between the two. First, try to get a good look at their wings. Both have two sets of wings, but a dragonfly's wings are similar in size and are broad at the base, where they connect to the body. A damselfly has more slender wings and they get more narrow as they move closer toward their bodies, according to Treehugger. 

Another way to tell the difference between the two insects is to look at how their wings are positioned when they are at rest. A dragonfly holds its wings straight out when it is not flying, while a damselfly folds its wings back so they are aligned with their body. Damselflies also have longer, more narrow bodies, so they appear sleek and slim, while dragonflies tend to be more broad and bulky looking. 

They have existed for millions of years

Dragonflies have existed for hundreds of millions of years and date back to a time even before dinosaurs roamed Earth. Scientists believe dragonflies have existed for about 300 million years, Smithsonian Magazine reports. They were some of the earliest winged insects to evolve.

The dragonflies from hundreds of millions of years ago looked similar to the dragonflies we see today, but on a much larger scale. While most dragonflies today have a wingspan of between 2 inches and 5 inches, fossil records show some prehistoric dragonflies had wingspans of as large as 2 feet, Smithsonian reports. Scientists believe that the high oxygen levels in the atmosphere during the Paleozoic era allowed dragonflies to grow to such large sizes.

They start their lives in the water

We often see dragonflies buzzing around near the water, but at the beginning of their life cycle they are fully aquatic. Females lay their eggs in the water in the summer, and they hatch about a week later, National Geographic reports. The larvae, which are called nymphs or naiads, can live in the water for as long as three years, depending on the species.

The nymphs are carnivores, eating insects, mosquito larvae and other aquatic creatures until they fully mature. As they grow, they molt as many as 15 times before reaching their full size. 

Once the dragonfly nymphs are mature, they emerge from the water and crack open their exoskeleton. This process releases its abdomen and wings, Smithsonian Magazine reports. Their wings will dry out and harden over the next several hours, and then they are ready to take flight. Their lifespan as adults varies by species. Some live just a few weeks, while others live for as long as a year. 

They have top-notch flying skills

Dragonflies can really fly. In fact, their flight skills are so impressive that they have inspired engineers to try to build robots and drones with similar capabilities. One reason for their inspirational flight skills is how their wings work. They have two sets of wings, and they can beat them individually or together, the San Diego Zoo reports. This capability allows them to fly like a helicopter. They can fly forward, backward and side to side and even hover in place.

Dragonflies also move fast in the air, with some species clocked flying as fast as 20 mph. And one species of dragonfly, the globe skimmer, migrates 11,000 miles across the Indian Ocean, completing the longest insect migration in the world.

Dragonflies' stellar flight skills help them catch prey. They mostly eat other insects, and they are able to grab them from mid-air with their feet, Treehugger reports. They are able to judge the speed and angle at which their prey is flying and then time their dive precisely to snatch it out of the air. They very rarely miss, with a 97% success rate. 

Their heads are all eyes

Even at a quick glance, a dragonfly's eyes are quite noticeable because of how large they are. Their large eyes dominate their heads, and they are so close together that their two eyes almost look like one, the San Diego Zoo reports. In contrast, damselflies have more space between their eyes. 

Dragonflies have compound eyes with as many as 30,000 individual lenses called ommatidia. This gives them a nearly 360-degree range of vision. Their eyes are very sensitive to light and movement, but compound eyes cannot change focus like our eyes do, so they can only see objects close to them clearly. They have binocular vision, which allows them to judge distances, Nature North reports. They also see in color, although like other insects, they cannot see the red wavelength of light. They can, however, see ultraviolet light, which humans cannot detect.