• Emma Hodson

Bot fly blog: My unwanted souvenir from Peru

Updated: Oct 28

Ever wondered what it's like having a bot fly in your arm? Read more to find out what it's like...


If you are squeamish I would advise you read no further...


What is a bot fly?

Dermatobia hominis, also known as a 'tórsalo' in Latin America,is a species of fly whose larvae parasitise humans and other animals. This fly can either lay its eggs directly into a mammalian host or into an intermediate host like a mosquito or a tick. The eggs can subsequently be passed on when they take a blood meal from a human host. Once inside the warm tissues of its host, the eggs are able to hatch and develop into larvae which continue to grow. Looking back on my bot fly experience: I'm in the middle of the Peruvian rain forest; it's fantastically diverse, incredibly vibrant, ridiculously humid and there are insects everywhere you look, sometimes bigger than the span of your hand! I was captivated seeing so many different species every single day. Although, I have to say I wasn't the biggest fan when they found their way under the mosquito net above my bed and I'd wake up to something very large buzzing a little too close to my face for comfort. And then there's the ones that bite and sting, which is quite a lot of them! Every day I wake up with a new array of bug bites covering my entire body. The ankles seem to be the worst, I've now lost count of how many I have there. There's a new bite on my forearm as well- this is nothing out of the ordinary, it just looks a bit larger than the others. I've submitted to the fact that any amount of insect repellent I use ultimately has no effect at all. The insects of the Peruvian rain forest are truly relentless. Don't get me wrong, as a zoologist I love insects-they fascinate me and I have a deep respect for their role in our ecosystems and food chains. However, when they have managed to bite every inch of my body from head to toe and my skin is red and raw from scratching so much, I begin to question my love for these little creatures.



It's 4am and the persistent beeping of my alarm under my pillow marks the start of a new day. There are no walls here at the research center so I take a moment to listen to the chorus of the waking forest: the croaking of the frogs from the creek close by, the deep-throated call of the waking howler monkeys ringing across the forest. At this time it's relatively cool even though the air hangs heavy with humidity. This is the only time of day when there is a slight respite from the insects that will start to gather with the rising sun.


Several weeks have passed and my new bites are either open and raw, itching to the point of driving me to insanity or have partly closed over in an attempt to try and heal briefly before another one takes its place. The one on my forearm is slightly raised and feels hard to the touch but I think nothing of it. At least this one isn't itchy like the others so I couldn't really care less what it looks like!


Time catches up with you in the rain forest and the business and excitement of everyday slowly merges into a blur and all too soon my two months here in the rain forest are over and it's time for me to move on. It's with great sadness that I depart from this phenomenal, wild, relentless place which I've come to call home for this leg of my journey.


I'm now in Costa Rica, listening to the waking bustle of the farm. It's very different to the chorus of the rain forest but it's still comforting hearing the gentle neighing of the horse and the clucking of impatient chickens wanting to be fed. The goat bleats in the distance. My arm is still sore, all of last night I felt sharp pains in my forearm and it may just by my active imagination but it almost feels like something is moving around inside there. The bite I thought nothing of is now raised and hard, it looks a bit like a target with a red ring around the outside and in the middle as well.


I go about my day as normal, feeding the dogs in the morning, taking the goat up to feed on the hillside for the day and chasing the chickens out of kitchen. In the afternoon I go back to the house to rest when I feel another stabbing pain from my arm. I look down at my bite and I do a double take. Something white is poking out of the centre of it and as I pull my arm up for closer inspection, the white thing retreats into my arm. So turns out I wasn't imagining things, there is in fact something living inside my arm.


Removal attempt number 1:

Having previously monitored the macaws daily in Peru for parasites and regularly removing bot flies from them, it immediately occurs to me that I might have something similar myself. That evening, I sit for close to an hour on my bed with my head torch on and a pair of tweezers in hand. The little worm-like thing in my arm is predictable in its behaviours, surfacing regularly, pushing out a clear-coloured liquid as it does so. I find that by dabbing the area where the liquid is coming out of dries the area up, causing the larvae to surface more regularly. However hard I try, I cannot grab the larvae from my arm- it seems impossible to get hold of and is remarkably quick to dart back into the depth of my forearm.


I next try a technique which we used on the macaws- applying a layer of Vaseline on top of the hole, cutting off the supply of air and oxygen, forcing the larvae to the surface to breathe. I have no explanation as to why this didn't work on the larvae in my arm, as it partly surfaced but still not enough for me to grab hold of it. Looking back now, it did look quite different from the bot flies which the macaws had so I'm not entirely sure that's what it even was. It definitely wasn't responding in the same way. Another hack which people recommend is putting a layer of meat such as raw bacon on top of the hole which is also supposed to draw it out. However, given that I'm volunteering on a vegan farm, there isn't much of that about!



Time for a trip to the local 'doctor'

Given that attempted removal with tweezers and suffocation with Vaseline didn't work, I decided that a trip to the local 'doctor' was needed to decide on the best course of action. And you'll see why I say 'doctor' in inverted commas in a moment. Normally, this man I was going to see about my bot fly works in a bar. But if you let him know you are coming and go to his house, he changes into a white lab coat and takes you round the back of the house to this little annex that has been made into a waiting room and small doctor's office. There were cages of various birds and a couple of dogs out the back as well. It was all a very bizarre experience. The room which had been turned into a doctor's office was very sterile and clean, once you were inside you wouldn't have known you weren't in a hospital room!


What happened next is not for the faint hearted. To try and make the hole large enough to try and get anything out of it, he disinfected a needle which was then probed around in my arm. It was uncomfortable and painful and not sure that this achieved a great deal if I'm completely honest! The opening on my arm was sterilized, and we agreed that trying to squeeze it out would be the best course of action. Let me tell you now it wasn't pleasant. Lots of liquid of various different colours came out of my arm and to be honest the lump did get noticeably smaller. After all this, the larvae had still not come out but with the lump a lot smaller, my arm was bandaged up and I was prescribed a tablet from the local pharmacy which kills all parasites in your body. I'd grown up taking these regularly in Mexico so it wasn't too much of a shock to be taking it again.


My mistake:

Now here comes one of the biggest errors on my part. After all this ordeal trying to get rid of it, the larvae was no longer visible and it wasn't surfacing at the opening in my arm. So in my mind, I kind of assumed that it had died and that that was that. I assumed that with time the lump on my arm would close and it would be fine. However, the opening continued to produce liquid regularly, which was not helped by me thinking that squeezing it to get as much liquid out as possible was a good idea. Long story short, for the next 3 months, possibly more, I didn't do anything about the raised lump on my arm that continued to produce liquid.


Something I should have done many months ago: After having this thing on my arm for about for about 5 months in total, I was finally persuaded to go to a proper clinic in a larger town in Costa Rica. Here, I received a local anesthetic and the entire section surrounding the lump on my arm was cut open. All the scar tissue which had formed inside my arm was removed and the whole thing was stitched up. The sample from my arm was sent off to pathology for further analysis. The results of this was that there was no larvae or trace of the larvae in that sample at all. So to this day I have no ideal what happened to the bot fly that was in my arm. Maybe my body just broke it down, maybe it came out and I didn't notice; I will never know...


Now, all I have left of my bot fly is a large scar on my forearm and every time I look down at my arm I'm reminded of my time in the rain forest in Peru and all the ordeals that came in the months to follow. They say every scar has a story: this one certainly does.




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