Bot Fly, aka Torsalo or Dermatobia hominis

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Anterior Orbital Myiasis Caused by Human Botfly (Dermatobia hominis)

Capt Randall L. Goodman, USAF, MC; Col Michael A. Montalvo, USAF, MC; Maj J. Brian Reed, USAF, MC; LTC Frank W. Scribbick, USA, MC; Chad P. McHugh, MPH, PhD; Randall L. Beatty, MD; Ricardo Aviles, MD

A 5-YEAR-OLD boy with inferior orbital swelling and an erythematous mass arising from the inferior cul-de-sac of his right eye (Figure 1 and Figure 2 to the right) was seen by an Air Force Mobile Ophthalmic Surgical Team working in a rural area of the Republic of Honduras. The respiratory pore of a late-stage larva of the human botfly (Dermatobia hominis) was located in the anterior orbit. The larva was gently removed under general anesthesia through a small incision in the conjunctiva (Figure 3, Figure 4, and Figure 5 to the right).

Figure 1. Five-year-old Honduran boy with right inferior orbital swelling and erythema.

Figure 2. Examination under anesthesia, demonstrating right eye chemosis and inferior cul-de-sac mass.

Figure 3. A large white larva being removed from the right anterior orbit through a conjunctival incision.

Figure 4. Complete late-stage human botfly larva immediately after removal.

Figure 5. Based on the morphology of the anterior and posterior spiracles and the exterior spines, the larva was determined to be a mature larva of the human botfly (Dermatobia hominis).


Ophthalmomyiasis refers to the invasion of the lids, conjunctiva, cornea, and rarely the orbit or globe of the mammalian eye by fly larvae (order Diptera). The sheep nasal botfly (Oestrus ovis) is the most common cause of ophthalmomyiasis.1 The human botfly (D hominis) is the most common cause of cutaneous myiasis in Central and South America, but few cases of external ophthalmomyiasis and no previous case to our knowledge of orbital invasion have been reported.2

The female botfly glues her eggs onto the abdomen of a captured mosquito or other common fly. When the carrier insect lands on a human, the larva, or bot, hatches, burrows into the skin, and positions itself "head down" to feed, breathing through caudal respiratory spiracles. A furuncle with a central pore develops as the bot matures, molting twice until reaching 18 to 24 mm. The larva withdraws through a central punctum, falling to the ground and pupating before emerging as a mature botfly.3 Chloroform or lidocaine to anesthetize the bot may facilitate surgical removal as does occluding the breathing hole with ointment, beeswax, chewing gum, or pork fat.4


Capt Randall L. Goodman, USAF, MC
Col Michael A. Montalvo, USAF, MC
Maj J. Brian Reed, USAF, MC
LTC Frank W. Scribbick, USA, MC
Chad P. McHugh, MPH, PhD
San Antonio, Tex

Randall L. Beatty, MD
Pittsburgh, Pa

Ricardo Aviles, MD
Tegucigalpa, Honduras


1. Savino DF, Margo CE, McCoy ED, Friedl FE. Dermal myiasis of the eyelid. Ophthalmology. 1986;93:1225-1227.

2. Wilhelmus KR. Myiasis palpebrarum. Am J Ophthalmol. 1986;101:496-498.

3. Lane RP, Lowell CR, Griffiths WA, Sonnex TS. Human cutaneous myiasis: a review and report of three cases due to Dermatobia hominis. Clin Exp Dermatol. 1987;12:40-45.

4. Elgart ML. Flies and myiasis. Dermatol Clin. 1990;8:237-244.

By Johany DeMarco

            There’s an insect nominated as the most disgusting, most vile, most revolting insect ever to fly on the face of this planet.  And it comes straight to you (I mean that literally) from the tropics of Central and South America.  You might want to keep a fly swatter nearby.  After you read this, it might really come in handy.


It cheerfully burrows way under your skin

Where it wiggles, lays eggs, its hooks sure do pinch!

Sooner or later its bound to come out

Out pops the maggot, how many?  You lose count!


It’s Bot Fly.  It’s Bot Fly

The worst of its kind

It’s Bot Fly.  It’s Bot Fly

You’re in for a bind

It’s Bot Fly.  It’s Bot Fly

They’re the worst of its race

I’d rather have pimples all over my face.

            Bot Flies not only make great songs to sing around a campfire on a cold and crispy night, but they also come in all sorts of varieties to meet your every individual need.

            There’s the Nose Bot Fly, also known as head maggots, which can’t get enough of sheep's and goats and other hoofed animals.  This grayish fly, about 15 millimeters long, deposits living maggots in the nostrils of sheep's.  The larvae, or maggots, crawl up sheep’s noses and remain in the sinuses for 8 to 10 months where they’re sneezed out of sheep’s nostrils.  The larvae pupates into an adult in the soil with the pupal period lasting 3 weeks or more, depending on the temperature outside.  Adults then emerge from the pupa and may live as long as 28 days.  Sheep's under attack from Bot Flies will run, gather in groups with heads down and rub their noses on the ground to prevent Bot Flies from laying their eggs.  These repugnant flies can cause blindness, severe head shaking, teeth gritting, and loss of appetite on these poor and innocent sheep.

            Then there’s the Horse Bot Fly.  These Bot Flies favorite pastime is laying their eggs on horse’s knees, lip hairs, jaws, cheeks, and horse’s food.  When the horses eat the egg-infested food, maggots hatch inside the horse’s stomach and intestines where they irritate the mucous linings of the intestines, rectum, and anus, making horses restless.  Some of the maggots crawl their way up the horse’s throat and into the horse’s mouth where they happily invade the tongue, gums, and mouth lining of the horse.  These happy little maggots party like there’s no tomorrow for 7 to 10 months on a major food binge!

            But the winner of the prestigious “Revolting Insect of the Year Award” goes to our dear friend, the Human Bot Fly, for its sincere demonstration of love and compassion towards the human race.  These pesty flies are very good at what they do.  They’re the Navy Seals of the insect world.  Human Bot Flies are not your average housefly.  They are scientifically classified as Dermatobia hominis, or myiatic flies.  You’re probably asking yourself what in the world does myiatic hominis mambo jumbo mean?  I don’t think you’ll be thrilled to know, but hey, because I’m such a nice person, I’ll tell you anyway.

            Since these guys are myiatic, they don’t waste time frolicking in your garbage cans.  They go directly to the source, and yes my dear friends, their favorite food on the menu is you!  In this article we will discover together the wonderful world of Human Bot Flies.  You will share in the joys of maggot birth and the miracle of puberty as these magnificent flies eject ceremoniously from underneath your skin and open their eyes for the very first time.

            Human Bot Flies are not tiny flies.  They’re pretty large and are nearly the size of bees.  They have a yellowish head, huge bluish-black thorax or body, with orange legs and brown wings.  These flies have an extremely powerful urge to reproduce.  If they were to fly towards you, not only would you hear their annoying buzz and notice how big they are, but you also would immediately try squashing them with your shoe.

            As you’ll soon find out, Bot Flies are not only cunning, they’re gifted with an IQ equal to Einstein.  They know the impending doom that awaits them if they’re seen flying in your home, let alone near you.  So what do they do?  They fly out and seek a mosquito or tick.  The lower their IQ count the better.  The Bot Fly then holds the mosquito’s wings to prevent it from escaping.  It then glues about 15 to 30 eggs at a time on the abdomen of the bloodsucking mosquito.  When the Bot Fly lets go of the mosquito’s wings, the mosquito flies away carrying the Bot Fly eggs.  The mosquito then prepares for landing on your warm body.  As the mosquito sucks on your blood, your body heat begins to hatch the Bot Fly eggs on the abdomen of the mosquito.  Once the eggs hatch and the mosquito takes off to find more blood to suck on, the tiny baby maggots burrow into your skin.  It takes about 5 to 60 minutes for these baby maggots to burrow completely under your skin, either through a hole they make for themselves or through the bite hole made by the mosquito.  You won’t even feel a thing, not yet anyway.

            These baby maggots position themselves head down inside your skin with 2 oral hooks which they use to tear your tissue while they feed on you.  The rows of curved spines along their body help anchor the maggots onto your skin.  While the maggots feed on you they make a hole in your skin so they can breathe and excrete waste.  For 6 to 8 weeks the maggots begin to grow big and strong, munching deliciously away on you.  As they mature, you’ll begin to develop sores that itch like crazy.  These itchy sores will then develop into egg-size painful boil-like sores that house the growing maggots and often ooze.  You will then feel a stabbing painful feeling due to the maggots tearing off your tissue while feeding and from their spines irritating your tissue as they squirm around.  You’ll be able to see and feel the maggots move and wiggle under your skin.  How gross!  Once the maggots grow fairly large, they will eat their way out of your skin where they fall to the ground and continue to pupate into adult flies.  The entire horrible life cycle, from birth to adult, takes around 3 months.

The legendary explorer Colonel Percy Harrison Fawcett, who ventured into the unknown tropical wilderness of South America, wrote about these Human Bot Flies.  The natives called them “Sututus.”  Let us allow Colonel Fawcett to relate his encounter with the Sututus.

            “Sututus were another trial for some of us: these are the grubs of a moth or mosquito which, after hatching from eggs left on the shirt, immediately bury themselves under the skin-usually on the back.  The little brutes could not be extracted until the sore they made was “ripe,” and even then it was an art to get them, for on being molested they clung to the flesh with sharp mandibles.  Tobacco juice sometimes helped, but killing them under the surface could bring on blood poisoning.  Later on, the Indians undertook the cure in their own way.  They would make a curious whistling noise with their tongues, and at once the grub’s head would issue from the blowhole.  Then the Indian would give the sore a quick squeeze, and the invader was ejected.”

            There’s a wonderful site on the Web where people who’ve had encounters with the Human Bot Fly can post their horrible stories.  Brenda and Mark Johnstone officially started the website after Brenda’s husband Mark was bitten not once but twice in the scrotum.

            On November 24th, 2000 Mark and Brenda remember traveling to Costa Rica to observe the magnificent Volcano Arenal eruption from the Los Lagos observatory.  At night, while Mark is changing his clothes, he feels a mosquito bite on his scrotum.  Right away he begins to experience a strange pain in his scrotum.  When he mentions it to Brenda they both talk about what on earth it could be, whether it’s a spider bite or an infected mosquito bite.

            Brenda remembers reading something in the guidebook Explore Costa Rica by Harry S. Pariser, from their first honeymoon trip to Costa Rica.  The author mentions in the book a strange bug called the “Bot Fly (Dermatobia hominis), whose larvae mature inside flesh.  An egg-laden female botfly captures a night-flying female mosquito and glues her eggs on to it.  When the mosquito is released and bites a victim, the host’s body heat triggers an egg to hatch.  It falls off and burrows in.  The larva secures itself with two anal hooks, secreting an antibiotic into its burrow, which staves off competing bacteria and fungi.  Its spiracle pokes out of the tiny hole, and a small mound forms which will grow to the size of a goose egg before the mature larva falls out.

            Should you be unfortunate enough to fall prey to a larvae- an extremely unlikely occurrence for the average visitor- you have three cures available.  One is to use acrid white sap of the matatorsalo (bot killer), which kills the larva but leaves its corpse intact.  Another is to apply a piece of soft, raw meat to the top of the air hole.  As the maggot must breath, it burrows upward into the meat.  A third is to apply a generous helping of Elmer’s glue or cement to the hole.  Cover this with a circular patch of adhesive tape; seal this tape with a final application of glue.  Squeeze out the dead larva the next morning.  The only other alternative is to leave it to grow to maturity, giving you an opportunity to experience the transmogrification of part of yourself into another creature.  It only hurts when the maggot squirms and if you swim, presumably because you are cutting off its air supply.  Don’t try to pull it out because it will burst.  Part of its body will remain inside and cause an infection.”

            Brenda knows right away what is bothering Mark.  They go online to find more information on the Bot Fly with no success.  When they return home Mark begins to notice 2 lumps in his scrotal skin, causing him severe and intense shooting pain throughout his scrotum and perineum.

            Brenda makes Mark an appointment with their general doctor.  After looking Mark over, the doctor says Mark has lice and prescribes him lice medicine!  An 8 year old can tell you the difference between lice and something that isn’t!  If it’s tiny, hops around and does cartwheels on your skin, then yeah, it’s probably lice.  Lice do not cause excruciating throbbing pain.  People with Bot Fly larvae embedded under the skin have not only been misdiagnosed by doctors, but also labeled as crazy and told they watch too much Sci-Fi on TV.  Doctors should really listen to their patients and educate themselves on this matter

On December 17th, 2000 Brenda brings Mark to the emergency room after a painful episode.  While Mark sits on the examining table, a lady doctor picks up Mark’s chart and says, “I’m not touching that!”   Wait a minute.  I thought it was lice?

             Hours go by.  A doctor finally arrives and Mark and Brenda tell him their horrible story.  The doctor stares skeptically at them and asks, “What other doctors are you seeing?  Are you on any kind of medication?”  The doctor then excuses himself and tells them he has to make a call to the Urologist concerning the matter at hand.

            What does the doctor really do?  He hurries to his computer and types the word “Bot Fly” on the Internet search engine.  Brenda sneaks up behind him and says,” There is a lot more information on the net if you want me to show you where it is at!”

            The doctor, taken by surprise, turns around and defends himself saying the Urologist is on his way.  It’s obvious the doctor did not know what Mark had.  If doctors don’t know they should say so.

            Dr. Michael Rashid, MD Resident of Urology, enters the scene shortly after.  Dr. Rashid believes Brenda and Mark’s story, even though he is somewhat skeptical.  They set an appointment for Tuesday, December 19.  When the day comes, Dr. Gabriel Rodriguez, MD and Assistant Professor of Urology, examines Mark.   Off they go to the operating room where vasectomies are usually performed.  Brenda is allowed to be with Mark during the operation.

            After Mark is prepped for surgery, the doctor, with Mark’s consent, takes photos of the sores.  Dr. Rodriguez tells Mark he has to cut deeper into the tissue.  All of a sudden, Dr. Rodriguez’s jaw drops open in surprise.  He exclaims, “It’s alive!” and tells the attending nurse to get a container and drop the Bot Fly maggot inside.

            While the nurse is checking out the maggot, Mark tells the nurse, “I read on the internet that those things can jump 6 feet!”

            The nurse quickly slams the lid tight on the container and sets it down.  Brenda takes the container and brings it over to Mark.  They both watch the large maggot squirm and wiggle about.  The doctor closes up the area in Mark’s scrotum and begins to get ready for Bot Fly #2.

            When they extract Bot Fly #2 it is still alive, obviously enraged that it was taken out of a cozy and warm environment.  All this reminds Brenda and Mark of the movie Alien.  Brenda says how one day Mark is complaining on how uncomfortable the stitches are.  She simply tells him, “Well now you have a little knowledge of what childbirth is like.”

“Yes, but I had twins!” Mark replies.

            Mark has healed and is doing fine.  They even have a special poem written to the version of “Twas the Night Before Christmas” by Bryan Springer about their ordeal.  Their website on Bot Fly stories is a must read!  It helps educate the unknown public about these vicious pests.

            If you ever find yourself traveling to the tropics of Central and South America and you feel a Bot Fly maggot crawling under you skin, here are some proven remedies that will help get rid of your new friend.

HOW TO GET RID OF YOUR BOT FLY (without doctor intervention)

1)       Pray that God reverse time so when you wake up in the morning this terrible nightmare never took place.

2)       Try super glue, not Elmer’s school glue.  One person who was bitten by the Bot Fly on his head used Elmer’s glue and found these maggots could eat and still breathe through the dried glue.  He and his partner suggest you try superglue instead because when you slob it on it dries fast.  When they peeled back the superglue they found part of the maggot sticking out trying to gasp for air.  They advice the surest way to get them out is to squeeze them out.  One maggot shot 2 feet into the air after being squeezed!   5 maggots were squeezed out from this person’s scalp through the superglue application.

3)       Take a little tobacco or heavy camphorated oil soaked in a small cotton ball and place it over the maggot vent hole with tape.  When the worm comes out 8 hours later pull off the tape and the worm comes out with it.

4)       Apply Tiger Balm to every mosquito bite.  Tiger Bam is rich in camphor.

5)       Epsom Salt.  One person infected by Bot Flies soaked in a tub of very hot water with Epsom salt for 45 minutes before going to bed.  To his surprise, the next morning the 2 bites he thought were spider bites had dead maggots sticking out, making it easier for him to extract them.

6)       Injecting Hydrogen Peroxide on the bite forces the little critters to come out.

7)       One person bitten by the Bot Fly says applying Icthamol, also known as pine tar, works great.  She says after you apply the pine tar, bandage the area and remove it in 2 days.   2 maggots were drawn out this way.

8)       Apply a very thick layer of Vaseline.  When the maggot’s body is poking out of the hole, quickly grab the maggot by the base and tug it out in one large movement.

9)       Squeezing the maggot out without killing it first is a bad idea because these nasty creatures have hooks that hold it strongly in place.  You also run the risk of splitting the maggot in half.  If that happens, the chance of you getting an infection is high.

10)     The Coke bottle suffocation method.  Light a cigarette.  When you blow the smoke into a Coke bottle hold it over the breathing hole and wait for the larvae to poke its head out of the hole to get some fresh air.  Once you see its head poking out place your thumbs around the hole, apply intense pressure, and push like there’s no tomorrow.   Watch out though.  These maggots are known to shoot 6 to10 feet or more into the air when they’re squeezed out!  You can also use forceps or large tweezers to extract the maggots out.

11)    And the best way to remove Bot Fly maggots is not to remove them at all!  Let it complete its life cycle and fall out on its own!  There have been obsessed Entomologists who have purposely placed Bot Fly maggots on themselves in order to get a good specimen of an adult larvae, which is rarely captured, for their collection.  This might be taking their profession a little too far, what do you think.

Every year returning tourists from the tropics of Central and South America

unknowingly bring home with them a new friend.  Think of it as a free souvenir.  Air travel has been the best way for Bot Flies to sneak into other countries and by-pass metal detectors at the airport without being suspected.  People could be in another part of the world before the maggot has completed its breathtaking life cycle.  As a result, this can cause the accidental introduction of an exotic species of fly into that country.  What a great way to make new friends!

            How do you protect yourself from Bot Flies?  You can place a sterile plastic bubble around you and your home and never venture outdoors, but that wouldn’t be much fun now, would it?

            The Centers for Disease Control and Prevention suggest you do the following in avoiding mosquito bites, which remember, can carry Bot Fly eggs!

1)       Apply 30-35% DEET insect repellent to exposed skin every 3 to 4 hours when outdoors.  You wouldn’t want one of those eggs hatching on your nose.

2)       Wear long-sleeved clothing and long pants if you are outdoors at night.  And don’t forget to wear a hat.  You wouldn’t want to suffer sleepless nights due to maggots squirming and moving under your scalp!  It has happened.

3)       Spray an insecticide or DEET repellent on your clothing.  Mosquitoes are known to bite through thin clothing.

4)       Spray the insecticide Pyrethrin or something similar all over your bedroom before going to bed.

5)       Use a mosquito net over the bed if your bedroom is not air-conditioned or screened.  Spray the net with the insecticide Permethrin for additional protection.

Next time you travel to Central and South America, please don’t forget to carry your bug spray, unless you’re looking to make new friends.  Carrying a fly swatter with you at all times is not a bad idea.  If you don’t you never know.  The one fly you shooed away after it bit you could have been carrying Bot Fly eggs.  Surprise!  In a couple of weeks you might be giving birth to a beautiful pair of healthy twins!  Welcome to parenthood!


Fawcett, Colonel Percy Harrison.  Lost Trails, Lost Cities.  Funk and Wagnalls Company, 1953.

Wilkins, Harold T.  Secret Cities of Old South America.  Adventures Unlimited Press, Illinois, 1952.


Campos Pereira, M.  University of Sao Paulo:  Institute of Biomedical Sciences, Department of Parasitology.  1 March 2003


Department of Natural Resources, State Michigan.  Warbles.  3 March 2003


Goodman, R.M. Montalvo, B. Reed, F. Scribbick, C, McHugh, R. Beatty, and R. Aviles.  Casado Internet Group.  Bot Flies, aka torsalo or Dermatobia hominis.  26 February 2003>.

Oklahoma State University College of Veterinary Medicine.  Order Diptera.  4 March 2003>.

Department of Medical Entomology.  Exotic Myiasis.  Non-Biting Flies.  2 March 2003



Vandevelde, Alexander G. M.D.  Malaria Prevention: A Serious Matter for the Tropical Traveler.  February 1997.



Johnstone, Brenda and Mark.  Home Page.  <>.

Botfly Stories. <>.

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Several parts of this story and the photos are from Brenda Johnstone,, or for more stories about botflies click here. You can email Brenda at Much thanks to her for her information and her permission for us to use it.

And for Brenda's "Botfly Stories", CLICK HERE.
For links to other bot fly and related websites, CLICK HERE.

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