The different species of the Simulium damnosum complex are identified by their chromosomes, and Simulium yahense is one such species.
The Bioko form of Simulium yahense was discovered in 1990, and is unique to the island of Bioko - part of the Republic of Equatorial Guinea - off the coast of west Africa.
It differs chromosomally from mainland populations. This makes the island populations genetically distinct and they are probably a different species.
However, this was never confirmed - the test for different species is that they do not interbreed and are genetically distinct where they live together. In this case, the 2 chromosomal ‘forms’ lived on the mainland and the island of Bioko respectively.