Pete Williams, Gulf Breeze, Florida, August, 2008
The Dobsonfly's larvae are called "hellgrammites," and spend most of their lives under water in fast-moving parts of streams and rivers. After the adult dobsonfly mates, the females lay eggs on a branch or on rocks near a stream. Between 100 and 1,000 eggs are laid in a mass with a white substance over it. The eggs resemble bird droppings, which may protect from predators. After the hellgrammites hatch, they either fall into the stream from an overhanging branch, or crawl to the water.
This animal spends most of its life (two to three years) as a larva, living underwater. Hellgrammites live under rocks to avoid predators, especially fish. It ambushes other animals, especially aquatic insects, such as larvae of dragonflies, damselflies, stoneflies, and mayflies. Hellgrammites have strong jaws and can draw blood from a human if not handled carefully. They use these jaws to take apart their prey. Hellgrammites also have little hooks on their abdomens which allow them to grab onto items so that they don't get swept away in the current.
Hellgrammites are not very good swimmers. They move mostly by crawling. When Hellgrammites are full-sized, they crawl from the water to pupate (form a coccoon). They hide under a rock or log near the water, and overwinter as a pupa. The following summer, the adult Eastern Dobsonfly emerges to mate. They do not eat. Dobsonflies live only a few days. Eastern Dobsonflies are often attracted to lights at night.