Living organisms are known by scientific names. These binomial names can vary greatly in length, and some can be very short; genus or species names composed of only one letter are not allowed by any of the nomenclature codes, but any combination of two letters and above can be valid if it has not been previously used. This list of shortest species names lists the scientific binomials with the fewest letters. The longest scientific species names can be found in the List of long species names.
4 letters
Ia io Thomas, 1902 – Family Vespertilionidae. The great evening bat is the largest vespertilionid bat, reaching a wingspan of just over half a metre. It occurs in tropical Asia where it lives in limestone caves. Apart from being the shortest scientific name of a living organism (and one of the shortest possible, since anything below 4 letters would not be allowed), it also has the peculiarity of being composed only of vowels. The specific name probably refers to Io, a woman of classical mythology, viewed as "flighty;" and the genus Ia (ἰά) is a Greek term for a shout. †Yi qi Xu et al., 2015 – Family Scansoriopterygidae. This was a Jurassic theropod dinosaur that had an elongated finger which supported a patagium, akin to those of bats, which enabled the animal to glide between trees. The name is derived from Mandarin Chinese (翼 yì and 奇 qí, pronounced "ee chee"), meaning "strange wing".
5 letters
Aha ha Menke, 1977 – Family Crabronidae. This species of Australian wasp was named as a joke by entomologist Arnold Menke. He mentioned later that it was named for his exclamation "Aha, a new genus", when he first saw the specimen, with fellow entomologist Eric Grissell doubtfully responding "ha". It is found in the Kununurra region in Western Australia. Foa fo D. S. Jordan & Seale, 1905 - family Apogonidae. Known as weedy cardinalfish, this is a marine fish species of Indo-Pacific distribution, the type locality being the Philippines. Both the genus and species name derive from the word fo, Samoan for "cardinalfish". Ja ana S. Ueno, 1955 – Family Carabidae. This is a blind carabid from the Ja-Ana Cave near Gifu in southern Japan. However, the original genus Ja has been reclassified as a subgenus of Jujiroa, so its valid binomial name is currently Jujiroa ana (11 letters).