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.
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.
Mating
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.
Eggs
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.
Larvae
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.
Pupa
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.
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!
Reader Emails
Our readers have always been fascinated with the transformation of these bugs from eggs to hellgrammites and completely different-looking dobsonflies. Read on to learn more about their experiences with this bug at various life stages.
Letter 1 – Dobsonfly
WHAT IS THIS CREATURE??
Mon, Jul 9, 2007 at 6:59 AM
Dear Bug-Guys,
I saw this creature outside my job today. I work in Jamaica, Queens, NY — I
have never seen this bug anywhere before – EVER! I didn’t even try to google
it or anything — I just turned to you guys.
Its about 4″ long, with large wings covering its body up to its head. Its
got two bulging eyes that were looking right at me while I was taking its
picture. Let me tell you it knew I was there and it didn’t look happy! I
think it was hurt because it didn’t attack or fly away — it just kept
circling around to look at us. Its got two antennae and two very large
pincers near its jaws.
Please help identify this thing.
Oh, and just so you know, we didn’t kill it. My coworker and I got it to
climb onto a stick and we moved it off the sidewalk and onto a grassy patch
by the LIRR train station so it’d be safe. Thought you’d appreciate that.
Have a good one,
Pete from Brooklyn
Hi Pete,
Actually, from May through July, this is one of our most common identification requests. This is a male Dobsonfly, a perfectly harmless creature. The female Dobsonfly has much smaller, but considerably more formidable mandibles. The big mystery for us is why your email from nearly two years ago just entered our inbox today.
Letter 2 – Dobsonfly
lantern fly?
Thu, Jun 18, 2009 at 7:56 PM
I found this weird bug outside by the light on the side of my house in the appalachian foothills of NC. We live out in the country and see some strange bugs/moths, but this is super weird!! Any thoughts?
Sarah
Nebo, NC
Hi Sarah,
This is a Dobsonfly, and it is one of our most common summer insect ID requests. It appears that your specimen is a female, though the angle does not allow us to fully view the mandibles. the mandibles of the male Dobsonfly are much longer and formidable looking, though the female is more inclined to bite. Though the bite may pinch, it is harmless. A few days ago we received another image of a Dobsonfly, but have not managed to post it yet. Perhaps we will hunt for it now.
Letter 3 – Dobsonfly
HELP! Darth Vader bug (what is it?)
Mon, Jun 15, 2009 at 6:08 PM
We were on vacation in the mountains of North Carolina, staying at a cabin in the woods. Every night, insects would come out of the forest and land on the outside walls around the porch lights, Mostly moths of various kinds (Including 2 luna months), but these two bugs were bizzarre!
We don’t have any idea what they are. Can you help?
I am sending you pictures of both of them.
FIREHAWK
The Globe, near Blowing Rock, NC
Dear FIREHAWK,
We don’t like to post letters with unrelated insects as it compromises our archiving system. This is a female Dobsonfly, and it is the second example we are posting today.
Letter 4 – Dobsonfly
Would like help identifiying this insect
July 27, 2009
My husband took these photos in early to mid June on the side of our garage. He said this critter seemed very interested in the wasps nest that was up under the overhang. I have never seen such a thing and out there, i have seen some crazy looking “bugs”. There are cornfields nearby and a small spring fed creek on the property (however, its 150 yds from where this was taken)
Ann Matlock
Central Indiana, USA
Hi Ann,
We just finished posting an image of a California Dobsonfly, and our response mentioned the eastern Dobsonfly, Corydalus cornutus, and then we opened your letter, only to find an example. Your photos are of a formidable looking but harmless male Dobsonfly. Dobsonfly larvae known as Hellgrammites are aquatic and are prized by fisherman.
Letter 5 – Dobsonfly
mystery bug in Virginia
June 3, 2009
About 10 years ago in Amelia, VA I found a bug outside our camping tent. I did not have a camera at the time, so my description may be very vague. It was brown, about 3 inches long, and had large pinching mandibles that might resemble those of a stag beetle. Its wings were rather large, covered most of its body, and (if I remember correctly) were laid flat on its back in a triangular shape. They were not transparent and had a brown and black color pattern to them. I only got a brief glimpse of this scary-looking insect before I ran from it (I was only 9 at the time). I do recall seeing a preserved specimen of this same species at a zoo, and I think the name attached to it might have started with the letter D. As I’ve said before, my description is based off of a 10 year memory of a bug that I’ve only seen once. Any kind of identification or suggestion of what it could have been would be greatly appreciated, as I have been trying to find it online for the past few years.
Megan
Amelia, Virginia, USA
Hi Megan,
Both your excellent description and your drawing indicate that you saw a Dobsonfly ten years ago. We are sorry we were unable to respond when you wrote in June, as we were in Ohio visiting Mom. Upon our return, we had so much mail we ignored most of it until the past few day when we are responding to some requests at random. We are posting your letter and drawing to What’s That Bug?
Letter 6 – Dobsonfly from Burma
Subject: Unknown bug
Location: Northeast India/Burma boarder
May 5, 2014 9:18 pm
found this guy in Northeast India on the Burma boarder.
Signature: Wayne
Hi Wayne,
This looks like a female Dobsonfly in the family Corydalidae to us, but North American species are not this colorful. Male Dobsonflies have much larger mandibles. Piotr Naskrecki has an image of a yellow Dobsonfly from Costa Rica on his Smaller Majority blog. Your individual may be
Nevromus austroindicus based on this Wikipedia posting.
