It is neither a fly nor a bee but a rove beetle, distinguished by its short wing covers. This beetle does not bite or sting. It is however well known, and feared, for the burns or skin irritation that it causes on human skin.
The beetle has a corrosive ‘chemical’ known as pederin, which is contained in its haemolymph, the invertebrate equivalent of blood. Pederin is released when a beetle is unintentionally brushed against or crushed against flesh, leading to chemical burns on the skin. The production of pederin relies on the activities of a symbiotic bacteria that lives within the beetle.
Because of these burns, the Nairobi fly is sometimes referred to as a "dragon bug” or “acid-bug."
Adult beetles are predominantly black and red in colour, and measure about 1 cm in length. Their head, lower abdomen, and wing-covers are black, with the thorax and upper abdomen being red – enough warning.
The beetles live in moist habitats. Heavy rains provide the conditions for the Nairobi fly to thrive. The beetle lives in bushes surrounding houses, in which it hides during the day but at night it emerges attracted by fluorescent and incandescent lights and as a result, inadvertently come into contact with humans.
Severity of the skin irritation (dermatitis) depends on the affected individual, the dose of pederin and duration of contact. Mild cases result in a slight redness of the skin. Moderate cases will start itching which later develop blisters. More severe cases could happen if the toxin is more widespread over the body or the area becomes secondarily infected. Treatment involves washing the irritated area with cool soapy water.
Affected individuals may inadvertently transfer pederin to other areas of the body, such as the genitals, the face or eye. If the eye is affected, because of hand rubbing, it can cause conjunctivitis – also known as “Nairobi eye”.
The Nairobi fly should be blown or gently brushed off your skin if it does land there. It should not be squashed or crushed. Should the beetle fluids get into touch with your skin, wash the afflicted area with soap and water.
Despite its name, Nairobi fly is not only found in East Africa. It is found in most of tropical regions.
