River Dragonflies

Over 40 species of dragonflies can be found along the Riverway including this widow-skimmer.

NPS/VanTatenhove

What is a dragonfly?

Most people are familiar with the four-winged insect that has a long body and colorful markings. They are sighted flying quickly or hovering as they look for prey. Dragonflies are predators, whisking other flying insects into a trap formed by their hairy legs. Their powerful jaws chomp through their prey starting with the head first. The fossil record includes dragonflies with 3-foot wingspans and indicates that dragonflies appeared on earth well before dinosaurs.

Dragonfly Checklist listing 51 species recorded in St Croix National Scenic Riverway. 4/2004

 

Dragonfly Life Cycle

A dragonfly's life begins underwater after the female lays her eggs, dropping them into water or inserting them into a plant or sand near water. The egg hatches into a larva after about 10 days.

Dragonfly larvae live underwater for several years—up to 8 years in some species—eating other aquatic insects, tadpoles, and even small fish to survive. They shed their outer skin as they grow.

To escape from predators such as fish, dragonfly larvae can shoot water forcefully out of the ends of their abdomens which propels them quickly away from danger.

Once a larva is ready to become an adult, a transformation occurs. The dragonfly stops eating and crawls to the edge of the water. It climbs onto something that it can hold firmly and begins to gulp air to expand its body.

The outer skin then splits behind its head. Slowly, the adult dragonfly pulls itself out of its outer skin. The wings unfurl and the dragonfly rests as it dries. Once dried, it usually flies away from the water to hunt its first meal. The empty skin left behind is called an exuviae.

 

The life cycle of a dragonfly includes time underwater.

NPS/Galland

 

Damselflies can fold their wings together, something dragonflies can't do.

NPS/Nelson

Dragonfly or Damselfly?

Damselfies are a closely related group of insects that, at first glance, look very similar to dragonflies. But the shape of the wings and how they hold them is a key feature that distinguishes these two groups.

Dragonfly's rear set of wings have a broader base and are larger than the front pair. When sitting still, they hold their wings flat. Both sets of wings on a damselfly are the same size and shape, and when they rest they can fold their wings together.

 

The St. Croix snaketail dragonfly was discovered at this national park.

Matt Berg

St. Croix Discovery

Biologist William Smith collected dragonfly exuviae at County Road O Landing on the St. Croix River during the summer of 1989. He noticed that some of the exuviae looked different from the others. He took them back to the laboratory and looked at them under a microscope.

He then collected live dragonfly larvae. The larvae were raised to adults in the laboratory. As the adults emerged, it was clear to biologists that they were looking at an unknown species.

The new species was named Ophiogomphus susbehcha, the St. Croix Snaketail Dragonfly. It prefers clean, large river habitat in particular between Norway Point and Marine on St. Croix.

Learn more

 

For more information about dragonflies in National Parks: