As stated in the ICZN Appendix B, specific names always begin with a lower case letter, simple as that. And technically no sentence should begin with a specific name. From ICZN (International Code on Zoological Nomenclature) Appendix B:
6. The scientific names of genus- or species-group taxa should be printed in a type-face (font) different from that used in the text; such names are usually printed in italics, which should not be used for names of higher taxa. Species-group names always begin with a lower-case letter, and when cited should always be preceded by a generic name (or an abbreviation of one); names of all supraspecific taxa begin with an upper-case (capital) letter.