Headlines and Titles of Works

Q. I work on science textbooks and science trade books (I wonder why I’ve never needed to ask this question before) and have this question: Does one capitalize “sp.” (or “spp.”) in titles? For example: “Dinarda Spp.: The Sneaky Thief.” Unabbreviated, the word “species” would be capitalized. However, were it the actual species name, it would be lowercased. It does look odd capitalized, since it is never so in text, but I’m leaning toward capitalization as being correct. Possibly the answer to this question lies within (within CMOS, that is), but if so I’ve not been able to find it. What say you?

A. CMOS comes close to answering this question. According to paragraph 8.159, which outlines the principles of headline-style capitalization (a.k.a. title case), the second part of a species name is always lowercase in a title, even if it’s the last word in the title or subtitle. So,

Dinarda dentata: A Sneaky Thief”


Dinarda maerkelii: Another Sneaky Thief”

And though we don’t quite say this in CMOS, more than one species of the genus Dinarda would follow the same pattern, even when the abbreviation “spp.” (species, plural) stands in for the names:

Dinarda spp.: The Sneaky Thief”

In sum, use lowercase for “spp.” (and for the singular “sp.”) wherever it occurs in a title or heading. Thanks for giving us this opportunity to clarify our rule.