The name Nairobi fly or Kenya fly is applied to two species of beetle

Beetle

Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...

 which live in East Africa

East Africa

East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...

, Paederus crebinpunctatus and Paederus sabaeus. They are species of the rove beetle

Rove beetle

The rove beetles are a large family of beetles, primarily distinguished by their short elytra that leave more than half of their abdomens exposed. With over 46,000 species in thousands of genera, the group is the second largest family of beetles after the Curculionidae...

 genus Paederus

Paederus

Paederus is a genus of small beetles of the family Staphylinidae . Due to toxins in the hemolymph of many species within this genus, it has given its name to paederus dermatitis, a characteristic skin irritation that occurs if one of the insects is crushed against skin...

, and are black and red in colour, and about 6–10 mm long. They live in rotting leaves where they lay their eggs.

The beetles neither sting nor bite, but their haemolymph

Hemolymph

Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...

 contains pederin

Pederin

Pederin is a vesicant toxic amide with two tetrahydropyran rings, found in the haemolymph of the Paederus genus of beetles, including the Nairobi fly, belonging to the Staphylinidae family. It was first characterized by processing 25 million field-collected P. fuscipes. It makes up approximately...

, a potent toxin that causes blistering and Paederus dermatitis

Paederus dermatitis

Paederus dermatitis is skin irritation resulting from contact with the hemolymph of certain rove beetles, a group that includes the genus Paederus...

. The toxin is released when the beetle is crushed against the skin. People are advised to brush or blow the insect off their skin to prevent irritation.

Heavy rains, sometimes brought on by El Niño events, provide the conditions for the Nairobi fly to thrive.Outbreaks have occurred in 1998 and 2007.