February 3, 2010
February 3 - Dermatobia hominis
The tórsalo or human bot fly, Dermatobia hominis, undergoes larval development in the skin of a vertebrate host. They frequently infest cattle, but can use primates, sheep, and other domestic and wild animals. The method by which larvae reach a host is unique among the family Oestridae. Adult female botflies catch a porter, which is commonly a mosquito, and lays eggs on it. This porter then transports the eggs to a vertebrate host during the course of its natural behavior (e.g., blood-feeding). The eggs hatch while the porter is on the vertebrate host, in response to body heat. First stage larvae gain entry to the host through the arthropod bite or hair follicles. In the host, larvae develop through three instars over 1.5 – 2.5 months. The boil-like lesion caused by the developing larvae stays clean through bacteriostatic action in the larval gut. After development, the maggot exits its host, drops to the ground and pupates in soil, emerging 1 – 3 months later as an adult fly.
In the tropics, where botflies are common, people specialize in popping bots (like American teenagers pop a zit). Massaging the site and knowing just when to press is a skill. Some people prepare the area first by applying an oily paste (e.g., petroleum jelly) to the site for several hours; this causes the bot to retract the cuticular spines it uses to hold itself in place and move closer to the surface as they breathe through a respiratory siphon that exits at the skin surface. Although some think that putting a steak on the furuncle caused by the bot will cause the maggot migrate to the other, more attractive, meat source;, the bot only emerges because it's suffocating. So, use petroleum jelly -- it's cheaper than steak! Prior to the extraction in the video, the site was kept under Vaseline and bandages for over a day, which is probably why it came out so easily. Please do not attempt extracting a bot by yourself – see a doctor. You could rip off the respiratory siphon of the larva causing it to die inside of you, where it might become infected - and then you'll have more serious problems than a baby fly temporarily using you as its home.
Contributed by Holly Tuten.
Video by Brandon Mellin, Clemson University.