The infamous botfly, which can actually EAT YOUR BRAINS!

Scientifically known as Dermatobia hominis the Human Bot Fly only happens to be able to parasitize humans, it can actually attack and occupy any number of large mammals and includes primates as well as humans.

The human botfly eggs have been shown to be vectored by over 40 species of mosquitoes and muscoid flies, as well as one species of tick;the female captures the mosquito and attaches its eggs to its body, then releases it. Either the eggs hatch while the mosquito is feeding and the larvae use the mosquito bite area as the entry point, or the eggs simply drop off the muscoid fly when it lands on the skin. The larvae develop inside the subcutaneous layers, and after approximately eight weeks, they drop out to pupate for at least a week, typically in the soil. The adults are small gray flies resembling a blowfly, but easily recognized because they lack mouthparts.

This species is native to the Americas from Southeastern Mexico  to northern Argentina, Chile, and Costa Rica though it is not abundant enough (nor harmful enough) ever to attain true pest status.

once  entered the skin of its victim. These particular insect larva have many adaptations to remaining into the skin. First and foremost there are the backward facing spines on the body. These anchor the stout body into place as it feeds. Also most of the body mass is below the narrow breathing tube which allows for the natural constriction of its hole to keep it in the host. Another more peculiar adaptation is under some debate, it appears the Bot Fly larva produces some sort of antibiotic that helps to keep the wound bacteria as it feeds.

As mentioned above, It is rare for patients to experience infections unless they kill the larva without removing it completely. It is even possible that the fly larva may itself produce antibiotic secretions that help prevent infection while it is feeding.

The larvae can grow anywhere in your body, it just depends on where the eggs wind up. Which could end up with you having a fat wormy thing in your tear duct. Or your brain. We know, because that's happened.