WHAT IS THAT ODD BULGE?
As a biologist, I sometimes judge the quality of my day by the wildlife I observe. I had been complaining about just that (only one box turtle and two indigo buntings noted) when my luck changed. While I was checking my live traps (small rodent traps which are designed to keep them alive), my wonderful assistant and I noticed some odd bulges in the genital region of the deer mouse we were measuring. I know this requires explaining and you are dying to know why I had live traps, why anyone would want to catch a rodent alive, and what kind of measurements were we taking? Perhaps I’ll explain later, but for now you should focus on the odd bulges in the genital region.
The odd bulges seemed to have an opening in the skin. Something was moving in there! We could see teeth-like structures moving back and forth. Instantly we recognized it. Botflies. Since we hadn’t ever seen one in real life, we decided to do some botfly removal. I zipped off to retrieve my dissecting kit from the truck (doesn’t everyone keep a dissecting kit handy?). The kit contained a narrow set of fine-nosed forceps. FYI, forceps are tweezers but you don’t get much scientific street cred for using tweezers. I often tell my students that “Tweezers are for eyebrows. Forceps are for science.” I like to propagate that kind of scientific snobbery sometimes and it is a subtle way to encourage grooming, Bonus.
Back to the odd bulges. I inserted the forceps through the opening and tried to grab the botfly. It wasn’t easy. As I pulled, the botfly extended its hooks to help it remain within its host. With a gentle tugging and pushing down on the bulge, the botfly slid out. It was huge! How did that little mouse possibly move? Not to mention the fact that the botfly was feeding on the mouse, eating it alive. We decided to place some antibiotic on our mouse friend (who looked relieved to be rid of its botfly) and let it go. I’d like to believe that little mouse is home; resting; glad to have met us; and telling his little mouse friends about the friendly giants. We went on to remove six more botflies from other mice.
So what’s the deal with botflies? Botflies that affect rodents (like our little mice friends) lay their eggs at the openings of mouse houses and runs. The mice walk past the eggs. The eggs stick to the fur and hatch when they feel the mouse’s body heat. The hatched larva enters into the mouse’s body through the anus, nose, mouth or other opening. It develops a bit and then apparently migrates to the preferred location. Apparently, the preferred location of a deer mouse is the genital region (inguinal area/groin). The botfly feeds on the mouse’s tissue and gets larger and larger and larger.
The botfly larva has rings of curved spines that allow it to remain within the host. It breathes from tubes (spiracles) that it sticks out of a small hole in the mouse’s body. It will remain there for a few weeks, before leaving the mouse. One source indicated this could take 10 hours. Imagine that mouse conversation! "Dude – you have something sticking out of your groin. It’s getting bigger. Dude – did you just poop that out? That is the biggest poop ever. Bob, come see this! Dude just made the biggest poop ever. EVER!" In my imagination, this mouse conversation occurs with a thick Jersey accent. That isn’t fair. It really should be a southern accent and would play out differently like this: "Darlin' – you have something sticking out just right there. No there. Oh, it’s out sweetie. Oh, bless your heart. You need to eat less fiber."
That botfly will drop out of its host, burrow into the soil and pupate. It will emerge as an adult and the circle of life will continue with or without accents.
