Bot flies, particularly the human bot fly, are insects whose larval stage can develop within the skin of mammals, including humans. These flies are primarily found in tropical and subtropical regions of the Americas, extending from southern Mexico down to northern Argentina. The female bot fly does not directly bite humans; instead, she lays her eggs on other blood-feeding insects, such as mosquitoes. When the carrier insect lands on a warm-blooded host, the body heat encourages the bot fly eggs to hatch, and the tiny larvae then burrow into the host’s skin, often through the bite wound or a hair follicle.
Identifying a Bot Fly Bite
The initial sign of a bot fly infestation, known as cutaneous myiasis, appears as a small nodule or bump on the skin. This lesion often resembles a boil, appearing raised and red, and it usually features a central pore or opening. This opening serves as a breathing hole for the developing larva to access air. Fluid, which can be yellowish, bloody, or clear, may periodically discharge from this central opening. Individuals might report a sensation of movement beneath the skin, particularly as the larva grows. While infestations can occur anywhere on the body, common sites include exposed areas like the limbs, scalp, neck, back, and breast. The presence of a firm, tender lump with a visible central pore and potential fluid discharge is a significant indicator of a bot fly larva.
Progression of the Lesion
Once the larva has entered the skin, it continues to grow within the subdermal cavity for six to ten weeks. As the larva matures, the nodule will enlarge, forming a pronounced, boil-like swelling often referred to as a “warble.” This growth can lead to increased discomfort, pain, and itching at the site of infestation. The larva possesses spines and hooks that help it anchor within the tissue, causing irritation. While secondary bacterial infections can occur if the site is not kept clean, bot fly larvae often secrete antibiotic substances that can reduce the risk of such infections. After completing its development, the larva will exit the skin.
Next Steps After Identification
Upon identifying a lesion that suggests a bot fly infestation, it is important to seek professional medical attention. Healthcare providers can confirm the diagnosis and determine the appropriate course of action. Self-removal of the larva is not recommended, as attempting to squeeze or forcibly extract it can cause the larva to rupture, potentially leading to complications. Medical procedures for removal often involve either surgical excision or occlusion methods. Occlusion, which entails covering the breathing hole, aims to deprive the larva of oxygen, encouraging it to emerge to the surface. Surgical removal ensures the complete extraction of the larva and proper wound cleaning. Following removal, appropriate wound care is advised to promote healing and prevent complications.