Most people who know me are aware of my fascination with parasites, and I know I’m not the only one. When I worked as an interpreter at the Bell Museum of Natural History in Minnesota, I found the best way to win the attention of a group of unruly kids was to show them something they all thought was disgusting. My calm command over the live snakes, spiders, scorpions and giant cockroaches invariably earned me the stunned respect of the students. Children love what is weird and creepy. They love what scares them. Adults might act more dignified, but they are no different. That’s why I know that secretly you want to hear about my botfly, Dave.
I acquired Dave while living in Honduras. It is no surprise to me that after a couple of months spent in a hot, humid environment at close proximity to cattle I had gotten infected. Nearly all terrestrial vertebrates get botflies from time to time, although some species are more commonly found with them than others. Typically each type of vertebrate host is infected only by its own specialized species of botfly, but as luck would have it, the so-called human botfly Dermatobia hominis is most commonly found in cows, and humans are just an accidental host.
Botflies infect their hosts by means of a vector, as the adult flies have no mouthparts or other organs by which to deposit their eggs on their host. Instead they place their eggs on a smaller blood-feeding insect, usually a mosquito, housefly or sometimes a tick so the botfly eggs can enter their host through the insect bite. Once inside, the botfly makes itself at home and will spend the next eight to twelve weeks growing and preparing itself for life as an adult fly.
As fond as I was of Dave, botflies are arguably one of the most revolting animals on planet earth. As adults they are a large, but relatively innocuous looking fly, but during their larval phase that they are undeniably repulsive. Before their metamorphosis they’re bulbous egg-sized monsters featuring several rings of back-wards pointing black hooks circling their amorphous bodies that hold them indelibly inside their host, a pair of black fangs near the mouth, and a long fleshy periscope that they use as a breathing apparatus coming out of the rear. Of course, if you are lucky enough to actually have a botfly, you probably won’t see most of this, because they spend the majority of their lives underneath the surface of their hosts’ skin. The only visible signs are usually an ever-growing lump with a tiny breathing hole at the center and an occasional twitch as they make themselves comfortable.
Other than his little periscope tail, the only time I ever saw Dave was during his third instar molt when he came up order to shed his skin. I did feel him, however. The vast majority of the time the botfly was entirely painless, and I was able to ignore it completely. Very rarely, however, I would have a sudden, brief flash of pain so intense that I would find myself standing up and yelling before I realized what was happening. These sudden bursts made me seem slightly insane, and the explanation of having insects in my skin didn’t really dispel this notion. I have heard that they will cause pain when something affects their breathing tube, but for me the pain seemed to occur at random, and I suspect it was simply the moments when the feeding worm came across a larger nerve.
Although occasionally painful, botflies are virtually harmless if left alone. Once they finish developing inside their host they simply leave to complete their lifecycle, and the hole heals with remarkable rapidity. Because of their ability to keep the immune system at bay, it is only when they are killed but not properly removed that they pose a risk of infection. Still, removal is simple. All that is required is to cover their breathing hole in order to suffocate the worm and then to squeeze out the dead fly once its hooks disengage.
The reason I decided to put up with this painful, filthy nonsense for nearly ten weeks was so I could see Dave in all his glory when he finally matured (and so I could keep him in a vial and use him to weird out friends during dinner.) I wanted to see what would happen; it was a science experiment. After awhile, however, I grew attached to Dave on some sort misguidedly sentimental level, and I was excited to see him. I mean, hell, I did name him.
The problem is, botflies are evolved to exit their host as painlessly as possible so they can begin their pupation without being smashed or put into vial. Just as nature intended, Dave escaped from my leg without me even noticing. I simply returned from work one day with a hole in my life. I was genuinely depressed for a couple of days at losing my science experiment and pet. I’d like to think he’s at least grown up into an adult fly, but since I had moved to an arid climate since my infection, I doubt he’s had much luck in completing his lifecycle. …but who knows? Cattle are everywhere. I wish him the best.