Short Answer
Very few hyphenated specific epithets (i.e., species' names) exist due to the regulatory body (the ICZN) that governs the nomenclature code for animals. The code has multiple rules preventing hyphens and other marks/punctuation from being included in animal binomial names. If such marks originally existed when the species was first described, the ICZN code even recommends removing/updating those marks in all but 1 instance.
Hyphens are only allowed if they separate a letter used to describe some physical characteristic of the animal and the letter needs to be separated from some other word describing the letter.
- Example: Polygonia c-album is retained because this butterfly has a white ("album") shape on its wing shaped like the letter "c."
Long Answer
According to the International Code of Zoological Nomenclature from the International Commission on Zoological Nomenclature (ICZN), usage of a hyphen or other marks is not generally accepted in a specific epithet. There is 1 specific instance in which hyphens are permissible.
See relevant excerpts from the Code below (with bold text being my emphasis):
Article 27. Diacritic and other marks:
No diacritic or other mark (such as an apostrophe), or ligature of the letters a and e (æ) or o and e (œ) is to be used in a scientific name; the hyphen is to be used only as specified in Article 32.5.2.4.3.
First, let's look at Article 32.5 more broadly to see its scope in removing characters followed by some sub-articles demonstrating common instances in which hyphens are not appropriate.
32.5. Spellings that must be corrected (incorrect original spellings)
32.5.2. A name published with a diacritic or other mark, ligature, apostrophe, or hyphen, or a species-group name published as separate words of which any is an abbreviation, is to be corrected.
32.5.2.2. In a compound species-group name published as separate words that are deemed to form a single word [Art. 11.9.5], the component words are to be united without a hyphen.
32.5.2.3. In a compound species-group name published as words united by an apostrophe or a hyphen, the words are to be united by removing the mark concerned (but see Article 32.5.2.4.3).
32.5.2.4.4. If the first element is a Latin letter or group of Latin letters not identifiable as fitting into the preceding three categories, punctuation (if any) must be deleted and the components united.
Etc.
Finally, Article 32.5.2.4.3 indicates the only instance that hyphens can be used:
32.5.2.4.3. If the first element is a Latin letter used to denote descriptively a character of the taxon, it must be retained and connected to the remainder of the name by a hyphen.
- Example. c-album, in Polygonia c-album, so named because a white mark on the wing of the butterfly is similar to the letter c.
BONUS: Plants
Note: hyphens in plant scientific names is more common.
- E.g., Carya carolinea-septentrionalis, Smilax bona-nox, Ribes non-scriptum
The reason? The International Code of Nomenclature for algae, fungi, and plants doesn't have as strict of rules preventing their usage. For example:
60.11. The use of a hyphen in a compound epithet is treated as an error to be corrected by deletion of the hyphen. A hyphen is permitted only when the epithet is formed of words that usually stand independently, or when the letters before and after the hyphen are the same (see also Art. 23.1 and 23.3).
20.3. The name of a genus may not consist of two words, unless these words are joined by a hyphen (but see Art. 60.12 for names of fossil-genera).
23.1. The name of a species is a binary combination consisting of the name of the genus followed by a single specific epithet in the form of an adjective, a noun in the genitive, or a word in apposition (see also Art. 23.6). If an epithet consisted originally of two or more words, these are to be united or hyphenated. An epithet not so joined when originally published is not to be rejected but, when used, is to be united or hyphenated, as specified in Art. 60.11.
