Dobsonfly adults are all bark and no bite

The eastern dobsonfly may look intimidating but the larvae are the real predators

By Marisa Baldine |
1/2 Dobsonflies are large insects with a wingspan of up to five inches. (Photo courtesy of gowan/iNaturalist CC BY-NC, cropped)

Usually, fear is the first emotion people feel when they see a dobsonfly. They are one of the larger flying insects in the Chesapeake region and have jaws that look like they came out of a horror movie. To add to their intimidating appearance, dobsonflies are nocturnal and clumsy in flight, so people usually encounter them at night. Does having a four-inch-long bug with one-inch-long jaws flying around at night not sound appealing? Fear not; they are far more interesting than frightening.

It turns out that only the males have incredibly long jaws, and the only ones they will attack are other male dobsonflies. They use their long jaws to compete with other males for territory. Female dobsonflies have shorter and more powerful jaws but only use them for self-defense, as adult dobsonflies do not eat.

Dobsonflies live for less than two weeks in their intimidating adult form but can live for years as larvae in local streams. The larvae are known as hellgrammites. Hellgrammites can grow up to be up to three inches long, and their appearance has been compared to a centipede. They have brown bodies with a large head, big mandibles and a segmented body. Each segment of their body has a set of legs and feathery gills. Hellgrammites hide under rocks and along the bottoms of streams. Unlike the adult dobsonfly, hellgrammites are ferocious predators that will eat almost anything that flows past their hiding spots, including small fish. The hellgrammite lives an eat-or-be-eaten life at the bottom of our streams, as it is also a favorite food of many fish.

So, the most important thing to remember about dobsonflies is that when they look their most intimidating, is when they are least threatening, and when they are in their larval stage, watch out for this fierce predator! At any stage, dobsonflies are a promising sight. Their reliance on clean, fast-flowing streams with rocky bottoms makes them a good indicator of stream health. The adults don't stray far from the water and rely on streamside vegetation to lay their eggs in the right place. They aren't as sensitive to pollution as other insects, like mayflies and stoneflies, but they can still be a good indicator of overall stream health.

They might give us the creepy crawlies, but the steep decline in insect populations is cause for concern, and conservation efforts that help them and other Chesapeake critters should be celebrated. Insects are often the base of the food chain and an essential indicator of the health of local ecosystems. Unless you're frequently wandering near streams at night, it's unlikely you'll encounter an adult dobsonfly. If you do, be thankful for the opportunity and know it is a sign of clean water near you. Enjoy the opportunity and keep your fingers safe from those mandibles.

Are you interested in protecting your local waterways? Visit our "Help Protect the Bay" page to learn about actions you can take in your everyday life.

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wildlife Stream health

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