How do dobsonflies ward off their predators? Does their large size keep others away, or do these insects also fall prey to bigger animals and bugs? Here are some interesting dobsonfly defense mechanisms that are unique to them.
The Dobsonflies are one of the most fascinating aquatic insects, with over thirty species found in North America, Canada, and Mexico.Â
These large creatures (some of them can grow up to five inches) with scary-looking pincers on their front can be enough to make you run away from an average Dobsonflies.
But in their natural habitat, how do they protect themselves? In this article, let us explore the life and behavior of the Dobsonflies.
Dobsonfly Defense Mechanisms
Like any other type of insect or animal in the wild, Dobsonflies have a wide range of special defenses against predators.
These creatures are built differently, with pincers, jaws, and wings that help them survive and keep natural hunters away.Â
Their Large Mandibles
The first thing you will notice about adult male dobsonflies is their large mandibles in front of their head. These are shaped like sharp sickles.
These mandibles are used during mating or as a defense against other males. The mandibles make up almost the whole head and can grow up to 1 inch in length.Â
Adult males have mandibles larger than females. They use these to attract and hold the females during mating. However, these are not powerful enough to pierce animal skin.
On the other hand, the mandibles of the females are short and sharp. These do not contain any venom but are enough to inflict painful bites on predators, including unsuspecting humans.
Foul Odors
Dobsonflies have a chemical defense to their advantage, common to many other insects.
The insects have Malpighian tubules as part of their excretory system, which releases a foul-smelling anal spray.
This mechanism is often used as a last resort to ward off their enemies.
Their Size
Humans, as well as animals, are intimidated by the large size of these creatures. For natural predators of the Dobsonflies, their size itself becomes a defense mechanism.
These insects can grow up to 5 inches long, with a wingspan about twice the size of their bodies.
The larva of Dobsonflies, commonly called Hellgrammites, also grows between 2-3 inches.
These insects are considered one of the largest insect predators in the water, eating worms, different types of flies, and small fish.
The size of Dobsonflies is one of the reasons that most predators stay away from hunting them.
Hellgrammite Defense Mechanisms
Hellgramites are the larval form of Dobsonflies. These are comparatively smaller than adults but are still one of the largest aquatic insects.
The larvae have their own defense mechanisms, which are effective in protecting themselves from their predators.
Eggs laid out like bird droppings
Birds are one of the major predators of Dobsonflies and Hellgramites, so the insects have found a unique way to protect themselves in plain sight.
Dobsonflies lay eggs in clusters, arranged in three layers, and the mass is covered by a clear fluid that turns white over time.
The eggs resemble bird droppings which most birds or predators ignore. Therefore, making it the perfect hiding spot for the eggs and newly hatched larvae.
Sharp Pincers
Hellgramites resemble adult Dobsonflies in terms of the structure of their mouth. These insects have very sharp mouthparts that can easily pierce the skin of animals.
Like adults, the male larvae do not have sharp pincers to pierce. Female hellgramites have pincers that can pinch, cause painful bites to animals, and even draw blood.
Frequently Asked Questions
Can a dobsonfly hurt you?
Yes, there is a chance that female dobsonflies can hurt you if you handle them incorrectly.
These insects have sharp pincers that can pierce the skin of humans and animals.
Female dobsonflies are the only ones that have these sharp mandibles, however, and can cause painful bites. The males cannot do it.
How does the dobsonfly fight?
Dobsonflies use their large mandibles if they have to defend themselves against other potential mates of their love interest.
For females, the mandibles are the greatest defense mechanism they have. They use these to keep away any threat and pierce the enemy, causing painful bites.
What do dobsonflies turn into?
Dobsonflies are the final life cycle of the insect. They hatch into larvae called Hellgramites which live underwater for two to three years.
After pupating for a brief period, they hatch into winged insects called Dobsonflies. The adult dobsonflies live for only about a week, and their only purpose is to mate and produce their offspring.
Why dobsonflies are called hellgrammites?
There is no specific answer to the etymology of Hellgrammites.
Historically, fishermen are known to call aquatic bait hellgramites.
These insects are used to this day as effective bait to catch fish. However, the origin of their names is unknown.
Wrap Up
Whenever we find a scary-looking insect, our first resort is to get them out of the way and avoid them. It works as a defense mechanism against something we consider a threat.
Similarly, a threatening appearance or chemical release is the defense mechanism for creatures like the Dobsonflies.
The important thing to remember is that it is all part of nature’s fascinating way of protecting every creature in its unique manner.
Thank you for reading, and look out for bug bites around the water!Â
Reader Emails
Many of our readers have reached out to us to learn about the defense mechanisms of the humble dobsonflies over the years.
Read the emails below to understand the interest.
Letter 1 – Another Dobsonfly Pupa
I live in Elkhart Indiana ; I found this in a park in Goshen Indiana & I couldn’t find anything on the net about it, what could this be. Obviously it dead, we couldn’t keep it alive. I like your site, keep it up.
Joe McKalips
Hi Joe,
This is the second Dobsonfly Pupa photo we got in two days. It is dormant and will emerge, probably very soon. The adults are quite frightening looking.
Letter 2 – Another Dobsonfly Drawing?
Mary Hoeper
Hi Mary,
We believe your fabulous drawing and descriptive text is representative of a Dobsonfly, probably a female.
Letter 3 – A Pair of Dobsonflies
Letter 4 – Andean Dobsonfly from Peru
Letter 5 – Dobsonfly
Reader Emails
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Hellgrammite
I don’t know what kind of larvae this is but I never saw one quite so big. He is about 4 inches long and about ? inch thick. I live in South Central Pennsylvania USA. I am near water if that helps. This guy was crawling along my basement floor and I thought maybe you would know what he turns into or what he is? Thanks,
John
Hi John,
You have discovered a Hellgrammite, the larval form of a Dobsonfly.
Letter 2 – Hellgrammite
Hello!
I saw this critter on the side of the Virgin River in Zion National Park in southwestern Utah, heading for the water. What is it? Unfortunately, my picture came out blurry, and I didn’t put anything in the pic for scale, but he was about 4-6 inches long. My coworker guessed it was a beetle larva. Thanks!
Sarah
Hi Sarah,
This is a Hellgrammite, the larva of the frightening looking, but harmless Dobsonfly.
Letter 3 – Peruvian Hellgrammite
Hi I took a picture of this strange bug in southern Peru (near Machu Picchu). My professor says it is a rove beetle, but I think it moved in an "inch worm" fashion, so I am not convinced. What do you think?
Heather
Hi Heather,
We would love to know what the locals in Peru call the Hellgrammite, the larva of a Dobsonfly.
Letter 4 – First Hellgrammite of the Year!!!
This is a picture of a bug that we found while camping in west Georgia. We found 3 of these creepy fellows and not really sure what they are. It looks like they have six legs, and several other spikes pertruding from their body behind their legs (at first it looked as though they had 20 legs).
This is our first Hellgrammite photo of the year. The Hellgrammite is an immature Dobsonfly and a choice bait for fishermen.
Letter 5 – Emily's Hellgrammite Metamorphoses into Pupa
Hello again, Bugman!
I decided to keep my hellgramite. It is enjoying its indoor pupal chamber quite well. It has begun to pupate, but becomes very active when I lift the flat rock it’s under to check on it. Do you think it will hatch into adulthood before winter hits? Thank you!
Emily
Hi Emily,
Thanks for sending us documentation of your Hellgrammite’s metamorphosis. We aren’t really sure how long the pupa stage lasts.
Letter 6 – Hellgrammite
Hello again, Bugman!
I found this beauty today. My first hellgramite, and about three inches long. It was in a pupal chamber in sandy soil, under an overturned card table near the Missouri River. It copped an attitude pretty fast when I tipped the table up (I was hoping for a snake!). Anyway, I noticed you didn’t have any hellgramite photos on the page. I’m sorry the lighting is so bad. I decided to put it in a bowl of water for one shot, to get some of the sand off. I think I’ll let him go tomorrow. Thank you,
Emily
Hi Emily,
Long, long ago when we set up our website, we created separate pages for the larval Hellgrammites and the adult Dobsonflies. You can find other Hellgrammite images on their own page.
Letter 7 – Hellgrammite
Please identify this bug. We saw it on a bike path next to the New River in Virginia today.
Ashby Hopkins
Here are more pictures. I thought it might be a Coach Beetle at first, but it did not have long antenae. Thank you,
Jim Hopkins
Hi Ashby and Jim,
This is a Hellgrammite, the aquatic larva of the Dobsonfly. The winged adult males have frighteningly large mandibles, but they are docile and harmless. The females, on the other hand, will use their smaller mandibles to bite, but a harmless pinch is all that will result.
Letter 8 – Hellgramite
Found in an old building situated next to a stream!!! I’ve never seen anything like this……… What is it???
Greg in NJ
Hi Greg,
This is a Hellgramite, the larval form of the Dobsonfly and favored bait of fishermen.
Letter 9 – Hellgrammite
Hello,
My name is Josh, I will attach a picture of a bug that I found this weekend while walking down the side walk, it was in the area of Ceder Falls Iowa, I was with in less than a 1/4 mile of a river and the area I found it in is a little bit swampy as well, I am wondering if you could tell me what kind of bug it is? the first picture of it is sitting on the ground, the next it is hanging from a stick by it’s jaws, in the second picture of it you can see the bottom of it, thanks again, and I’ll await your response,
Josh
Hi Josh,
The Hellgrammite is the larval form of the equally fierce-looking, winged Dobsonfly.
Letter 10 – Hellgrammite
Letter 11 – Hellgrammite
My kids and I found these bugs in a damp, walking tunnel in Central Wisconsin. They were 3-4 inches long and had big, sharp pinchers that they used violently to defend themselves. They are very prehistoric looking. My guess is that it is some type of larvae. What are these, and are they usually lightning fast and deadly poisonous (LOL)?
Thank you,
Tom Curiouski
Hi Tom,
If you think the Hellgrammite is frightening, you should see the adult male winged Dobsonfly. Both larvae and adults are harmless. Hellgrammites are a choice bait for fishermen.
Letter 12 – Warning to Fishermen!!!!!!!
Hellgramites
Hello,
I know I just emailed you about a wasp but I was reading your hellgramite section and was thinking that you might think of warning novice fisherman about those pincers. My husband and I love to fish (he handles the bait… yes I am too squeamish, and in the case of hellgramites, I am afraid of being pinched!). Whenever we catch hellgramites for bait, he always takes a pair of pliers and snaps off the business end of those pincers before attempting to use them as bait. He neglected to do so once… I have never heard him yell so loud! I laughed so hard I could hardly fish (at the time it was hilarious). I thought that people who aren’t familiar with using hellgramites as bait but would like to try it might want this useful tidbit of information.
Mande Hyre
Letter 13 – Hellgrammite
I was hiking at McConell’s Mills in Western Pennsylvania and happened across this bug sitting in the middle of the street. It appears to me to be some sort of beetle larva, but it’s SO big. It also had this fancy move it did when we touched its head with a stick – it would curl its tail under [which was soft like a catepillar’s body] to quickly launch itself backward a few inches. Here it is pictured with my boyfriend’s finger [who, for scale, is 6’4″]. And here is another better picture of its face. I also have a video i took of it walking and doing its cool backwards launch maneuver, which you can have if you’re interested. PLEASE tell us what kind of bug this is. We’re absolutely dying to know. I almost regret not taking it home with me! I just hope it didn’t wander back into the middle of the road. Thanks!
Jen and Glenn
ps. We also found a bunch of these really pretty red and black millipedes, which i’ve included a picture of. They were about 4 inches long.
Hi Jen and Glenn,
You have just encounted a Hellgrammite, the larval form of the Dobsonfly. These curious larvae are prized by fishermen as bait.
Letter 14 – Hellgrammite
I live in Austin, Texas and just found this nasty looking bug outside on my patio, clinging to the wall in the early morning below my porch light.
It has a large set of mean-looking pincers on the front of the head. The forward half of the body is dark, and the rear half is light tan and caterpillar-looking. I had to take the picture through the yogurt jar I captured him in. He is about 3.5 inches long.
I leave most outdoor bugs alone but was concerned that if I ran across him later accidentally, I might get a nasty bite. He aggressively threatened me as I repositioned the jar to get the photo.
If anybody wants him, come and get him!
Thanks!
Patty Pritchett
Dear Patty,
He is beautiful. He is an adult Dobson Fly, the larvae of which are known as Hellgrammites. The male has the formidable jaws which are used during the mating ritual in what humans might consider spousal abuse. They will not harm humans. We have additional information on our site.
Letter 15 – Hellgrammite
What is this thing? Michael
Dear Michael,
Definitely a Hellgrammite, the larva of the Dobson Fly. We have photos of adults on our site, and would love to post your photo with the letter. I just received another letter from someone who spotted one at her cabin in Virginia, but I had no image to show her.
Letter 16 – The Creatures
Hello Bug Person,
I saw your site and thought maybe you could help me and my roommate out. We have creatures. That’s what we call them, because they are unlike anything we’ve ever seen. In the last three places we’ve lived, we have seen the Creatures in our basement. They are similar to centipedes in that they are long, have many legs, and are creepy. But that’s where the similarities end. Centipedes are flattened with legs that look like this ^ with one joint, but these Creatures have 2 joints, like spider legs. They don’t have as many as a centipede but definitely more than 8. The legs are generally the same size too, not different lengths like a house centipede. they don’t have the front "fangs" like a centipede but a mandible similar to a spider’s – no antenae no little butt feelers. And they come in 3 different colors. I’ve seen very large ones (4-5 inches), black with white spots; others were just as big but dark brown; and just the other day, in our new duplex, we found a little one maybe 2-3 inches long and light brown. They are very fast and i even hit one with a book, cutting off its lower half, and the rest of it got away. Yeah, these things are evil. Nobody knows what these things are. We’ve had hunters, floridians, Arizonians, and other self-proclaimed bug experts, but we always get the same thing: a hideous blank stare and lonely nights in our basement. Can you tell me what the creatures are?
Alex,
Be afraid. Be very afraid. Scream Alex, scream for your life. You have Tinglers living in your basement. Barring the possibility that the horrific monster from the 50’s horror flick starring Vincent Price is in your basement, following you from house to house, I can think of several additional possibilities, though none seems to exactly fit your description.
Possibility #1 is the hellgrammite, the larval form of the dobson fly. These four inch long creepy crawlies normally live in or near streams, but we have heard reports of them being found in basements. Check out this website to see if the hellgrammite is your culprit. http://www.watersheds.org/blue/nature/gallery2/
pages/hellgramite.htm
Possibility #2 would be a sun spider or wind scorpion from the family Solpugidae. They move quickly, and can be found in basements, though I haven’t heard of any American species quite as large as the creature you describe. They are closely related to other arthropods called vinegaroons.
Possibility #3 would be a different type of centipede. Scolopendra polymorpha is a six inch long species of centipede that resides within the continental U.S. You can locate a photo of it and of the sun spider on this website. http://www.angelfire.com/oh2/USInsects/
Arthropods.html
I shudder to think that we here at What’s That Bug have entered the ranks of hunters, floridians or Arizonians with blank stares, but without more concrete information, perhaps a photograph or a drawing, and some hint of your coordinates on the globe, we’ve run out of possible id’s.
Several months back, this column tried to identify a bug based on an inquiry from Deb. Here is her letter:
Hi,
I almost had a heart attack last week as I saw the biggest bug I have ever seen! I work as a therapist in an upstate New York School. My office is in the basement. As I rounded the corner to answer the phone, something huge
was slowly crawling across the doorway on the floor. It was blackish grey, about 4 inches long with a flattish body. The head looked as large as my thumbnail. It appeared to have short spikey hairs on its body, and 6 legs protruding from its middle segment. The abdomen was very large and trailed behind the legs. I didn’t notice any antennae, but it may have had pincers on the mouth. Thank God for a brave custodial worker!!! Later in the day, another co-worker said that he collected those bugs for trout bait, and that they sprout wings and fly around. Please! That was the stuff of nightmares!!!!!!!! I swear that I have seen miniscule versions of this bug in my own yard and want to know if they are the same. Could I have these prehistoric monsters flying in my back yard???!!!
—Deb
Embarassingly, I misidentified the culpret as a large roach. It turned out, in fact, to be a hellgrammite, the larval form of the dobsonfly, which you have photographed. Locally, the California Dobsonfly (Neohermes californicus) can be found near streams, generally at higher elevations, hence the frequent use of the larva as trout bait. The hellgrammites are aquatic and are found in swift streams where they prey on other insects, but they can pass dry spells under rocks and debris in the damp stream beds.
Dobsonflies are members of a primitive order of insects known as nerve-winged insects, which includes other oddities like the ant lion and lacewings. All adult nerve-winged insects, including the dobsonfly, are feeble fliers and are predaceous upon insect pests, so they are beneficial.
Letter 17 – Hellgrammite in Natural Habitat
Letter 18 – Hellgrammite
Letter 19 – Hellgrammite
Letter 20 – Hellgrammite
Letter 21 – Hellgrammite
Letter 22 – Hellgrammites for Bait
Letter 23 – High School Science Experiment produces unknown Larva!!!
I live on the Delaware River and each year we have the hellgramites crawling up to our house, sometimes even in our house (we have found them in our bed).Someone left the screen on the slider open a crack. The way this man described the crawling is exactly as we see it each year, and then when they metamorphasis into the adult dobsonfly is a sight to behold, hundreds of these creepy critters flying in the night. As I write this letter I have a dozen adults on the side of my house. AS WE SAY EACH YEAR THERE HERE!!!
The mandibles are very megalopteran (like a dobsonfly or fishfly), but it’s difficult to decipher the appendages that should be at the end of the abdomen. Definitely need more info on the kind of water the leaf pack was placed in, where the leaves came from, etc. Megalopterans need oxygen from flowing water, so this critter may actually be an aquatic beetle larva of some kind, which can tolerate lower oxygen levels.
Thank you for your input. We never received any further information, and we are still quite curious what this “experiment” was expected to produce.
Great info – thanks. We found a large female on our garage door – we live in Northern Virginia near DC. I remember a huge swarm of these on my grandparents farm in Monroe County, WV and also recall them when we fished at Smith Mt Lake, but this is the first one I’ve seen in the DC area. Our house backs to a Potomac River tributary with a dam but it does have moving water. Should we anticipate a large hatch of these coming out of the water this summer? Hoping not.
Thanks again!
Kristy
Insect populations vary from year to year, but if conditions are right, you can experience large numbers.
Great info – thanks. We found a large female on our garage door – we live in Northern Virginia near DC. I remember a huge swarm of these on my grandparents farm in Monroe County, WV and also recall them when we fished at Smith Mt Lake, but this is the first one I’ve seen in the DC area. Our house backs to a Potomac River tributary with a dam but it does have moving water. Should we anticipate a large hatch of these coming out of the water this summer? Hoping not.
Thanks again!
Kristy
that bug is giant
What time of year can these be found in the meramac river in Missouri
Is it rare to find in durham nc? Have pics if needed. Weirdest thing ive seen in awhile. Tyvm for the info. Very helpfull
North Carolina is well within the range of the Dobsonfly.
looking to purchase hellgrammites, do you sell them and ship to places in wisconsin?
what do you charge if you do sell and ship them?
looking to purchase hellgrammites, do you sell them and ship to places in wisconsin?
what do you charge if you do sell and ship them?