Nature Notes: Dragonfly Daze
The hot days at the end of July and early August are often referred to as the “dog days” of summer. While I always thought they were named after pups too hot and lazy to move during this time of year, the name actually comes from the Greeks and Romans who noticed the star Sirius, in the canis major (dog) constellation, rises just before the sun during this time of year. These “dog days” are also the “dragonfly daze” of summer – although dragonfly populations explode in late June and July, many species are still on wing through early August and beyond. But where do they come from, where do they go, and how come these friendly bug eaters are only around for a couple of months!?
Actually, they’re around all year long, but if you’re looking to the skies to find ‘em in cold months, you’re looking in the wrong place. Of course we don’t see dragonflies zooming around all winter in subzero temperatures. They have adapted a rather interesting survival strategy to make it through our long harsh winters – all of the adults die off except for a few species, like the Green Darner, that actually migrate! Green Darner adults fly all the way to Texas in the fall and their offspring will return in the spring (usually one of the first species we see). Dragonflies go through incomplete metamorphosis, which means their life cycle as three stages instead of the four stages you would see in complete metamorphosis. They begin as eggs in the water, hatch into aquatic larvae or nymphs and then skip the pupating stage, instead opting to go straight to adulthood.
Most dragonflies spend their winters underwater as nymphs, in diapause (a resting state) in the “warm” mucky-muck at the bottom of rivers, ponds and lakes. A few species overwinter in eggs on the shoreline, which will be washed into the water in the spring and hatch into nymphs. Depending on the species, dragonflies may be in the nymph stage for only a few weeks or up to 8 years in some Asian species! Here, most of our dragonflies spend about 1-3 years as nymphs.
Nora raised dragonfly nymphs last spring – watch as it hunts for amphipods!
These nymphs survive underwater by breathing through larval gills and using their keen sense of sight and super sensitive antennae to be ferocious predators of the lake bottom. They devour other insect larvae (like mosquitoes!), other dragonfly larvae, tadpoles, and even small fish with a voracious appetite. In turn, they serve their part in the food web as prey to larger frogs or fish. As they eat, they grow, molting old tight-fitting exoskeletons for new, roomier ones.
Nymphs will molt several times before becoming adults.
When the nymph is ready to turn into an adult it has a day or two of diapause while the final changes are made inside of the larval exoskeleton. During this time the nymph often has its head above water as it becomes acquainted to breathing oxygen, like it will in the adult form. When it is ready, it will climb up onto a plant or rock, the thorax splits open, the adult form emerges small and deflated and spends several hours “pumping” up its body with hemolymph (insect blood) until it reaches its full adult size. You can often find these deserted exuviae, or the exoskeleton they left behind, cling to vegetation or other structures around the water’s edge.
When the exoskeleton has dried and hardened, the dragonfly will take its first flight and become a predator of the sky. With impressive compound eyes of 30,000 lenses, dragonflies have incredible sight. Pair that with the capability of sustained, highly maneuverable flight, antennae that work as anemometers to measure wind speed and direction, powerful jaws, and spines on their front legs that act as a grocery cart for prey, and you get a pretty formidable predator. Dragonflies will eat pretty much anything they can catch, including other dragonflies, butterflies, and have even been observed taking down a hummingbird! They may eat their prey on wing or take it back to a perch. A keen observer may find discarded butterfly wings or beetle wings under a dragonfly perch. If you’re lucky enough to get close to one eating, you can even hear the “crunch!”
Check out how a dragonfly can move each wing independently in this slow-motion video! This helps them have superior maneuverability in flight!
You can thank the dragonflies for eating an insane amount of insects and pests (nicknamed the mosquito hunter as some can consume hundreds of mosquitos in just one day). You think a lion or a wolf is a good hunter? Hate to break it to ya, but they ain’t got nothin’ on the dragonfly! Recent studies show dragonflies catch their target prey 95% of the time – a number that decimates the stats of all large mammalian predators. In fact, their precision flight and accuracy is so impressive, they have been used for military and private sector research regarding drone development and design!
Right now is a great time to get outside and see some dragonflies before they disappear in the fall! Many are feeding, mating, or laying eggs. Dragonflies are fiercely competitive for food and mates, so you may even get to witness a dragonfly brawl. If you’re near water, look for a female dipping her abdomen into the water to lay eggs. Males guard females while laying eggs so they may stay attached to the female, or I more commonly find them “hover guarding” – where the male hovers near by and quickly chases off any other males, sometimes with a loud clash of wings! As dragonflies are hatched in, feed around, and lay eggs in water, they typically don’t travel too far from a water source, so check out any nearby ponds, streams, lake shores, or wetlands for a look-see! Here are just some you might find!
Enjoy the end of summer weather, getting outside for some fresh air, and watching these remarkable hunters gobble up mosquitoes!