Dobsonfly Prey: Helpful Facts

What ends up being dobsonfly prey, as adults and larvae? What kind of food do they prefer? How do they hunt in the water as larvae? We look at all this in the article below.

Corydalus cornutus, more commonly known as the Eastern Dobsonfly, is a common insect found in eastern North America, Canada, and Mexico.

These soft-bodied insects are found near a body of water, making them a form of aquatic flies. Here are a few things you should know about these fascinating creatures.

Dobsonfly Prey: Helpful Facts

Do Dobsonfly Eat Anything?

If we look at adult dobsonflies’ life cycle, the most interesting thing is their eating habits. Adult forms live for only about a week, in which they solely mate and reproduce. 

You might find them flitting around near rivers and streams in late spring up to mid-summer.

The food they store in their pupal stage gives them the nourishment to stay alive for the few days of their adult life.

Dobsonflies are known for their sharp pincers and huge size (some can even grow to five inches long!), which makes people think they might bite or cause damage.

But in contrast to their appearance, they prey on other creatures only in the larval stage. The adult dobsonfly doesn’t eat anything at all.

While the females might take some nectar once or twice, the adult males are absolutely focused on only one thing – reproduction.

What Do Dobsonfly Larvae Eat?

Dobsonfly larvae are more popularly known as Hellgrammites. These larvae are two to three inches in size and actively hunt a large variety of insects.

These larvae are found in fast-moving water currents, eating almost anything they can find at the surface or just under it.

Some of the common things that hellgrammites eat are insects and small fish. They also eat insects, arthropods, worms, and other invertebrates available.

Interestingly, what they eat depends on what is available to eat. They are generalist predators and are content with eating whatever is available rather than picking and choosing.

As the larvae grow bigger, the size of their prey goes up. Larger larvae do not eat the smaller prey, even if it is easily found around them.

Hellgrammites are in fact, one of the largest predators in the water by the time they grow up to pupate.

As they grow bigger, they can feed on larvae of other species, such as net-spinning caddisflies, blackflies, chironomid midges, and mayflies.

Dobsonfly Prey: Helpful Facts

How Do Hellgrammites Catch Their Prey?

Dobsonflies have one of the longest larval stages among insects. They spend almost their entire lives as hellgrammites, living in rapidly moving waters of rivers and streams.

The hellgrammites stay under rocks underwater, where they wait to catch their prey. They have very strong pincers that they use to bite and slowly chew them.

One adaptation that these insects have evolved is a hook-like appendage near their posterior end, which helps them cling on to a surface in rapid waters.

This is useful because they can easily stay still while prey floats by. Hellgrammites are most active in a fast current, as there are a lot of smaller insects that get carried along with the water.

Another unique thing that helps these larvae survive and hunt in the water is their ability to swim in both directions, backward and forwards.

They have sensory and chemical ways to detect the presence of their prey and changes in their surroundings, helping them to hunt in deep waters. They also have eyes, which help them somewhat in their hunt.

What Eats Hellgrammites?

Found mostly near water bodies, hellgramites are the natural prey for many different types of fish. Bass is one of the common fish that feed on these larvae, inside and on the surface of the water.

Once they grow, dobsonflies become easy meals for birds and small animals.

Since fish like feasting on them, hellgrammites are often used as bait for them. These bugs are appropriate as bait for plenty of fish of different sizes.

Dobsonfly Prey: Helpful Facts

Frequently Asked Questions

What does a dobsonfly eat?

Adult dobsonflies have a very short lifespan during which they do not hunt or feed or anything. They get the required nutrition from the food they store as a pupa.
In their larval stage, these flies are known to hunt small creatures on the surface of water, including insects, fish, and larvae of mayflies and blackflies.

Do dobsonfly bites hurt?

Though dobsonflies are not considered as dangerous to humans, their bites can be painful. While the males do not bite, females can and will do so if you try to handle them.
The larvae have large and sharp pincers that can pierce the human skin, causing skin irritation, bleeding and painful swelling.
The effects of a bite will not last very long, but it has to be taken care of at the earliest to reduce the swelling.

Do fish eat dobsonflies?

Yes, their larvae are very common prey for different types of fish. Bass is one kind of fish that is particularly fond of dobsonfly larvae.

In fact, anglers often use the larvae as bait for fishing. As adults, they are also consumed by birds and other small animals.

What does Fishfly larvae eat?

Fishflies are underwater, carnivorous flies that are known to feed on small aquatic insects.
They feed on insect larvae, tadpoles, clams, and worms that they find underwater. The larvae of these flies are also large enough to feed on tadpoles and minnows.

Wrap Up

The ecosystem of aquatic animals like the dobsonfly and its larvae is quite interesting.

While you may be scared of how large and fearsome a dobsonfly looks, you should remember that they are not really harmful to you.

They have a short lifespan and in all probability, you might never encounter one again. Thank you for reading! 

Reader Emails

Over the years, many of our readers have sent us emails to understand the dobsonfly better. Learning more about the prey of insects helps us understand what role they play in the ecosystem.

Do go through the exchanges below to understand the queries.

Letter 1 – Bring It On: Awesome Dobsonfly Photos promised


Hi Bugman,
I needed a picture of a Hellgrammite to send to a buddy. Yours are tops. I have long time experience with the hellgrammite.
We use them as bait for bass fishing. I have seen the adult Dobsonfly and it is larger and broader has a much stronger wing structure than your photos.
I will attempt to take some pictures of some local dobsonfly. The ones that you are showing wimpy.. Some of these hellgrammites are 4 to 5 inches in length.
Nice web site.
Best regards,
Joe B

Letter 2 – Dobsonflies and Fishflies


I was surfing around and found your site. Unfortunately, I do not have a picture of the bug that I am curious about, but it’s dimensions are etched permanently in my brain. I saw it in Tennessee and the most remarkable thing about it (to me) was just how large it was. The entire thing was slightly longer than 2" and as big around as my pinkie. It had two pairs of 1" wings on its abdomen (not the thorax region) that could well have belonged to a dragon fly, only they angled back like a fighter jet instead of straight out like a biplane. The thorax was used like a neck to articulate its head there were two round black eyes and very visible and pronounced mandibles that really looked perfect for biting my whole finger. It was way too big to splat. I put a jar around it and it stayed alive in there for days, following my every movement until I finally couldn’t take it any longer, mustered my courage, scooped the thing up (in the jar) and threw it into the pasture across the road. I’m hoping that, if you’ve ever seen anything like this, my words will be sufficient to help you identify it. I’d like to know what it is, its range of habitat and its function in our ecosystem. Thanks to you for your time and attention to this.
Very truly yours,
Jenna Casanova

Dear Jenna,
It sounds like it might be a male Dobsonfly.

Daniel~ By George, I believe you’ve got it! Thank you so much!

Letter 3 – Dobsonflies and Fishflies


Dear Bugman,
I was so thrilled to have a coworker identify this Hellgrammite and that I actually found your site to get further information. I live in the Harrisburg area and was quite amazed by this beautiful but scary thing perched on a patio chair around July 19. I thought this picture really showed him off well. He hung out a few hours on the back of the chair (I wasn’t about to chase him away!) and snuck away at some point. He was FOUR inches, and we live at least a mile away from the water (Susquehanna River and also Yellow Breeches creek), so I guess he lost his way. . . Thanks for being there

Dear Pat,
Wow, thanks for the awesome photo. We have recently gotten many letters, and most with photos, of Dobsonflies. We are soon going to update the website with a gallery of them. I can’t wait to post yours. He is a male, hence the enormous jaws. Thanks again.

Letter 4 – Dobsonflies and Fishflies


While walking with the kids by the river, I found the biggest bug I’ve ever seen. After I put in a cup and brought it home, we put it in a large jar. Then the task of looking up what the heck the bug was. Turns out, via your web site I found it, after about a half hour of searching google. Sure enough its a Dobson fly! Thank you so much for the information. The kids think its cool and scary at the same time, I’ve told them it’s harmless.
Judy Lillie,
Wausau Wisconsin

Yes Judy, the Dobsonfly is harmless. I’m so glad you found our site helpful. We have been getting numerous letters about Dobsonflies. Apparently, there was a dearth of information, or at least difficult to locate information on them before we went online. Have a nice day and keep appreciating insects for their amazing diversity and beauty. Might I recommend a video called "Microcosmos" that has amazing footage of insects, though unfortunately, no Dobsonflies. Have a nice day.

Letter 5 – Dobsonflies and Fishflies


Needless to say, we were all freaked out here at work when we saw this one. One of my coworkers found your site and we were finally able to name it. I thought this one came over on a boat from some foreign country… Nothin like anything i’ve seen before.
Thanks for the help!

Thanks for the amazing photograph.

Letter 6 – Dobsonflies and Fishflies


Thanks for posting a site that allowed me to identify this beautiful creature! I thought you’d like the photo as it is pretty nice. I’ve seen these all my life growing up in the Sierra Nevada mountains of California, but never knew what they were called (everyone else calls them ‘stone flies’) I also saw my first sun spider that same night. I think that is what it is, anyhow. It confused me with the appearance of having ten legs!
Thanks again, Anthony P.

Those Dobsonfly photos just keep coming.


  • 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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