Dobsonfly Life Cycle: From Tiny Eggs To Hellgrammites And Fearsome Flies!

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What is the dobsonfly life cycle like? Why is it so hard to find these bugs around you? Where do they live in their larval stage? Let’s find out.

Dobsonflies are aquatic insects living along streams and flowing water sources. Adults have a very short life span. Most of their lives as spent as larvae, also known as hellgrammites.

Dobsonflies belong to the Corydalidae family of the Megaloptera order. Nine genera of these insects have been discovered to date and are geographically distributed across America, Asia, and South Africa. 

Dobsonfly Life Cycle

According to biomonitoring studies, these insects live only in clean and unpolluted waters. They are unable to handle even the slightest bit of pollution in the water.

A beneficial insect for a healthier river ecosystem, dobsonflies are the primary predator for various aquatic species. 

The larvae are crucial in keeping the larvae of black flies and other pests in check and help control the breeding of these harmful insects. 

In this article, we look at the lifecycle of these huge insects and why they live almost their entire lives in the water.

Courtship Rituals

The male Dobsonflies are known for their distinctively large sickle-shaped mandible. For a long time, the mandible’s exact function was unknown. 

However, based on studies, adult male dobsonflies primarily use mandibles to fight with other male competitors during courtship. 

Most of the time, the male adults compete ferociously until one of them is severely injured or dead.

Once they win over the other competitors, they lay claim to the female by placing their elongated mandibles on the female. 

What makes this episode more interesting is that the mandible is placed perpendicular to the longitudinal axis of the female wings

They remain in this position for quite some time until copulation or unless another male dobsonfly arrives. 


As observed in numerous studies, male dobsonflies attach their spermatophore to the female genitalia during mating. 

The spermatophore contains a gelatinous mass that helps feed the female fly after the copulation.

Many even call the nutrient-rich content a “nuptial gift” that helps transfer the sperms into the reproductive tract of the female dobsonflies. 

Dobsonflies are short-lived insects; hence they can mate less frequently than most insects in this genera. 

The male adult flies live for 3 to 4 days, while the females have a lifespan of 7 to 9 days. Hence even single insemination has enough sperm to fertilize all female eggs. 

Dobsonfly Life Cycle


Female dobsonflies lay their eggs on the water surface almost immediately after mating. 

To prevent the eggs from being attacked by other predators, they hide them amidst leaves, branches, and other such areas with shade. 

They select spots in overhanging water streams that are difficult to access or see by other predators. 

According to Mangan’s study conducted in 1992, females lay up to 3 masses of egg clusters containing up to 1,000 eggs. 

These masses are laid in 1 to 5 layers and coated in a white protective sheath that prevents the eggs from overheating. 

The females have an unusual distribution pattern of laying eggs in patches. The eggs are left to incubate for 2 to 3 weeks, then they liquify to hatch, and the new larvae emerge. 

The larvae usually crawl into the stream immediately after dropping, probably due to their inborn affinity toward the water.


The hellgrammite larva is unique because dobsonflies have one of the longest larval stages among the insects of this family. 

Exclusively aquatic during this stage of their life cycle, the dobsonfly larvae cannot survive anywhere else other than the cool and clean running water of a stream.

The larval stage can last anywhere between one to five years, depending on the environmental condition they live in. 

During the entire lifespan, dobsonfly larvae can undergo molting at least 10 to 12 times. 

Molting is the process of shedding the outer skin. The larvae can grow up to 4 inches in size before pupating.

Anatomically, the dobsonfly larvae look very similar to centipedes. The head has a pair of distinctive pincers that they can use to deliver painful bites. 

The thorax segment of the body has three pairs of legs, followed by a segmented abdominal section with eight pairs of leg-like appendages known as prolegs. 

Dobsonfly larvae have gill tufts at the body’s base to help them breathe in water, along with a pair of anal prolegs (leg-like appendages) at the lowermost end of the body. 

The anal prolegs are like hooks that help stabilize the larvae’s body and prevent it from being swept away by the water current. 

Dobsonfly Life Cycle


During the pre-pupa stage, the larvae leave the water surface to reach soil near the river bank and pupate. 

They find a cool and wet area hidden under tree barks and crevices and create a hollow chamber for themselves.

They inhabit this chamber for 2 to 4 weeks before finally emerging as adult dobsonflies. The pupa has wings, antennae, and leg-like structures that are still developing. 

Adults can grow anywhere between one to five inches in size. They emerge from the pupa after approximately four weeks when the outer temperature is conducive. 

The soft-bodied insects have glassy wings with blotching patterns all over. Dobsonflies have three pairs of eyes and a pair of long antennae. 

One of the most distinctive features of a dobsonfly is the foul-smelling anal spray that they use as a protective mechanism when they detect danger. 

Frequently Asked Questions

Can a dobsonfly hurt you?

Despite the large mandible in adult male dobsonflies and the frightening size of the insect, the bite of a male dobsonfly is harmless to humans. 
They cannot penetrate the skin to cause any damage. Female bites, however, can be painful.
The larvae have finer pincers and can also give you a painful bite. These bugs should be handled carefully.

Are Dobsonflies rare?

Though Dobsonflies are not endangered insect species, they are a rarity in the wilderness. 

Found exclusively around flowing streams, they are specific to the geographic locations of North America, South Africa, and Asia. 

If you don’t live near a stream of running water, it is unlikely that you will ever see a dobsonfly. Moreover, the adults don’t live beyond a week, so it is hard ever to see them.

What time of year do dobsonflies hatch?

The Dobsonflies mate and lay their eggs during the summer and spring seasons. 
It can take between 2 to 3 weeks for the eggs to hatch. However, the process entirely depends on the optimal weather condition of the surrounding area.

What does a dobsonfly eat?

While the larvae are predators and feed exclusively on the stream invertebrates like worms, mollusks, and arthropods, the adult Dobsonflies don’t share this love for food. 
The female adults feed on nectar from flowers, while the male does not feed on anything during their short lifespan.

Dobsonfly Life Cycle

A Living Marker of a Thriving Biosphere!

Often used as bait by fishermen, the Dobsonfly larvae are crucial in keeping the freshwater streams free of pests and pollutants. 

The adults are beneficial insects and are helpful in pollination. They are a natural enemy of unwanted predators in the water and also a sign of a healthy aquatic ecosystem.

Thank you for reading!


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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