The Bug from "Hell"

These are possibly one of the most interesting aquatic macroinvertebrates that you can come across in the underwater world. What is found in our streams and rivers is the larval stage of a Dobsonfly. The Dobsonfly belongs to the Family Corydalidae in the Order Megaloptera. A more common name used for this larval invertebrate is the Hellgrammite.

Adult female Dobsonflies lay their egg cases near the water on overhanging branches or rock ledges. Once the eggs hatch, the larvae fall to the ground or directly into the water depending on where they were laid (be careful next time you decide to camp next to the water). The Hellgrammites then find shelter underneath rocks or logs in swift-moving water, such as riffles. For one to three years, the Hellgrammites will call these waters home until the time comes for them to leave and burrow into the bank where they become enter their pupal stage. The pupal stage can last anywhere from a few weeks to a month when they then emerge as adults. Adult Dobsonflies, like other aquatic macroinvertebrates that share this life cycle, only live for two things, to mate and reproduce. Adults will live for an average of 5-7 days, where the cycle will repeat once this time has passed.

Now, the Hellgrammite looks like an underwater centipede, but it only has 6 legs. The other appendages that you see are actually filaments that allow them to breath in their aquatic habitats, our example specimen has additional gill tufts at the base of those filaments. At the end of their bodies there are two hooks that extend out and anchor the Hellgrammite down. Looking at these pictures you may notice the large mandibles which they possess. When handling a Hellgrammite you must be careful, because they have been known to resist capture by being able to "pinch the blood" out of human fingers.

These unique creatures are a vital indicator of water quality. They survive best in relatively clean and well-oxygenated waters. Some outliers could be found in other conditions, but more often than not, you're going to see them in clean, cool streams and rivers. Not only are Hellgrammites a key invertebrate in their aquatic ecosystems, but they are also a fan favorite among Smallmouth Bass anglers. But whatever you do, DON'T be afraid if you come across one of these while wading in a stream. They will only bite if mishandled and feel threatened.