Rarest Dragonfly Saved by Speed Limits?

Saving America's rarest dragonfly may be as easy as slowing down. A new study shows that if cars abide by lower speed limits they could prevent deadly impacts with the insect.

The Hine's emerald dragonfly is the only dragonfly on the federal endangered species list. The insect's largest remaining population lives in Door County, Wis., though experts aren't sure exactly how many are left. There are at least 10,000 in Door County and up to 3,000 in the Chicago region.

Door County currently has two dragonfly warning-signs on roads near critical habitat areas, but South Dakota researchers set out to determine if dragonfly death rates were in fact linked with car speed.

Using GoPro cameras attached to a pickup truck, lead researcher Amber Furness, a University of South Dakota graduate student, drove the truck down Door County roads at speeds varying from 15 to 55 mph in increments of 10 mph. The cameras caught on tape each unlucky dragonfly's position before it hit.

The results showed that Hine's emerald dragonflies, as well as other types of the insect, could survive an impact below 35 mph. Faster speeds were fatal, however, and the insects are either killed after the collision or they suffer severe shock and fall to the ground, and are run over by a second vehicle.

"Insects are important too, and there are safer speeds that we can drive to try not to deplete their populations," Furness told Live Science.

While slower speeds don't necessary guarantee a kill-free zone, and spotting these tiny insects in time may be difficult, researchers suggest a 30 mph speed limit could help lower such deadly brushes with oncoming traffic.

"It may be easier to say we only need to do it during flight season, and during the day, but we need to make sure people are actually doing it, just like any speed limit," Furness said.

Dragonflies aren't the only species threatened when crossing roads. Florida's endangered panthers, Key deer and Hawaii's nēnē birds are all protected by speed limits and warnings signs. Their numbers are so low that car crashes could be detrimental to their population.

The Hine's emerald dragonfly can be recognized by its bright green emerald eyes and metallic body, with yellow stripes on its sides, the US Fish and Wildlife Service describes. They are only 2.5 inches long and have a wingspan of about 3.3 inches.

Historically, they were found in Alabama, Indiana and Ohio, but their habitat has now been reduced to just Illinois, Michigan, Missouri and Wisconsin, as far as we know. Urban and industrial development, pesticide use and changes in ground water have led to their depleted numbers.