Dobsonfly facts for kids
Quick facts for kids Dobsonfly |
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| Corydalus cornutus | |
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| Unrecognized taxon (fix): | Corydalinae |
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See Dobsonfly Homes |
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Dobsonflies are fascinating insects known for their impressive size and unique life cycle. They belong to a group called Corydalinae, which is part of the larger Megalopteran family Corydalidae. You can find their young, called hellgrammites, living in streams. The adult dobsonflies often stay near these streams too. There are nine different types (genera) of dobsonflies found across the Americas, Asia, and South Africa.
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The Name Game: Where "Dobsonfly" Came From
The name "dobsonfly" has been used for a long time, at least since 1878. People aren't entirely sure where the name came from. Back then, the larvae (hellgrammites) had many different nicknames. These names were especially popular among fishermen who used them as bait. Some common names included "Dobson," "Helgramite," "The Crawler," and "Stone Crab."
Dobsonfly Appearance: Adults and Larvae
Adult dobsonflies are some of the largest insects in places like the United States and Canada. Some species, like those in the Corydalus group, can have wingspans up to 18 centimeters (about 7 inches)! The Asian Acanthacorydalis fruhstorferi is even bigger. It can have a wingspan up to 21.6 centimeters (about 8.5 inches). This makes it the largest dobsonfly and one of the biggest aquatic insects in the world.
Their wings can be grayish or clear, depending on the species. They fold neatly when the insect is resting. Even with such large wings, adult dobsonflies are not very strong flyers. Their bodies are soft and can be yellow to dark brown. They usually grow up to 7.5 centimeters (about 3 inches) long. However, the largest Asian types can reach 10.5 centimeters (about 4 inches).
Spotting the Differences: Male and Female Dobsonflies
Male dobsonflies in many species are easy to spot. They have long, curved mandibles (mouthparts that look like pincers). For example, males of Acanthacorydalis, Corydalus, and Platyneuromus have these large mandibles. In some species, like Corydalus cornutus, these mandibles can be up to 4 centimeters (about 1.5 inches) long! Males use these long mandibles to compete with each other for females. Interestingly, these long mandibles are too long for males to bite effectively.
Female dobsonflies, on the other hand, have shorter, stronger mandibles. They can deliver a powerful bite if they feel threatened.
Some male dobsonflies also offer a special "nuptial gift" to females. This is a package of nutrient-rich food that the female eats after mating. Scientists have noticed that males with very large mandibles often give smaller or no food gifts. Males with smaller mandibles tend to give larger food gifts. The antennae of male dobsonflies are also usually longer than their mandibles.
Meet the Hellgrammites: Dobsonfly Larvae Underwater
The larvae of dobsonflies are called hellgrammites. They are perhaps more famous than the adults because they are easier to find. The famous entomologist John Henry Comstock wrote in 1897 that they are "very interesting to students of Nature study."
Hellgrammites are unique because they live underwater but can also breathe air directly. They take in dissolved oxygen from the water using special gills on their abdomen. They also have small holes called spiracles that let them breathe air when they are above water.
Hellgrammites have eight pairs of side "processes." They also have special hooks at the end of their bodies. These hooks help them hold onto rocks and other surfaces underwater. Their body color is typically black or dark brown.
Dobsonfly Homes: Where They Live Around the World
There are about sixty different species of dobsonflies. Scientists group these into nine main types, called genera. These different types live in various parts of the world:
- Some, like Neurhermes and Protohermes, are found from Northwest India to Indonesia, China, and Japan.
- One type, Chloroniella, lives only in South Africa.
- Others, including Acanthacorydalis, Nevromus, and Neoneuromus, are found from Northwest India to Southeast Asia.
- The Platyneuromus, Chloronia, and Corydalus types live from southern Canada all the way down to northern Argentina and south-east Brazil.
Dobsonfly Habits: What They Eat and How They Act
Hellgrammites live on the rocky bottoms of streams. They are mostly active during the night. They are ambush predators, meaning they hide and wait for their prey. They eat other aquatic insects like young mayflies, caddisflies, stoneflies, and chironomid midges.
Even though hellgrammites spend most of their lives underwater, people in places like Virginia and Pennsylvania have reported seeing them crawl out of the water during thunderstorms. This event is sometimes called "hellgrammite crawlings."
Adult dobsonflies are also active at night. During the daytime, they hide under leaves in the canopy of trees. They don't live very long, only about a week, and are not known to eat anything as adults. However, some have been seen drinking sweet liquids when kept in captivity.
Dobsonflies are sometimes attracted to mercaptan. This is a chemical added to natural gas and propane to give it a smell. This means they could act as an "animal sentinel," warning people if these gases are present.
The Dobsonfly Life Cycle and Reproduction
The metamorphosis from larva to adult in dobsonflies is a fascinating process. It begins with a special courtship dance.
Courtship and Mating Rituals
Male dobsonflies compete with each other to win over females. They aggressively flutter their wings. They also try to flip their rivals into the air using their long mandibles. After a male wins, he approaches a female and gently touches her with his antennae. At first, the female might seem a bit aggressive, moving her head and opening her mandibles. But then, she allows the male to come closer. He places his mandibles over her wings in a specific way. They stay like that until the female signals she is ready to mate.
During mating, the male gives the female a special, nutrient-rich food package. The female then eats this package.
Laying Eggs: The Start of a New Generation
Female dobsonflies lay their eggs at night, usually on rocky walls near streams. In the Corydalus group, this happens from May to September. They deposit coin-sized egg masses. Each mass contains about a thousand tiny, gray, cylindrical eggs. The female covers these eggs with a chalky, white substance. This coating likely protects the eggs from drying out and getting too hot. Females often lay their eggs in groups at a few specific spots.
From Tiny Egg to Adult Dobsonfly
About one to two weeks after the eggs are laid, they hatch. The first instar larvae either fall directly into the stream or quickly find their way to water. There, the larvae live for a long time, up to five years. During this time, they shed their skin (molting) 10 to 12 times as they grow.
When a hellgrammite is fully grown, it leaves the water. It finds a safe spot, like under a rock, a log, or even human-made debris. This spot is typically close to the stream, but sometimes they travel up to 40 meters (about 130 feet) away. There, they build a small chamber for pupation. They spend several days to several weeks as "prepupae" before shedding their exoskeleton.
Then, they become a pupa for about one to two weeks. The pupae are yellow-orange with dark spots on their back. They are covered in minute hairs. Although the males have a slightly wider head than the females, their mandibles are not as noticeably long as they will be in the adult stage. Finally, the adult dobsonfly emerges from its chamber, leaving behind its old larval and pupal skins.
Why Dobsonflies Are Important
Hellgrammites are very popular as fishing bait for anglers. Their large size, toughness, and active movement in the water make them especially attractive to fish like smallmouth bass. Fishermen often catch them by placing a net downstream and disturbing rocks upstream to make the hellgrammites float into the net. Because they are so popular, they can be quite expensive at bait shops. This has led to concerns about over-collecting in some areas, and their sale is regulated in certain states. Some anglers prefer to use artificial lures that look like hellgrammites instead.
Hellgrammites are also important because they are sensitive to polluted waters. This means they can be used as indicators of good water quality. If you find many hellgrammites in a stream, it's a good sign that the water is clean!
Adult dobsonflies are strongly attracted to lights. Because of this, scientists and collectors often use special lights, like black lights or mercury-vapor lights, to catch and study them.
Images for kids
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Protohermes grandis
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Corydalus cornutus
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Nevromus austroindicus
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A hellgrammite, the larval form of Corydalus cornutus.
