The Torah commands in Parashat Shemini (11:44), “Ve’lo Te’tame’u Et Nafshotechem Be’chol Ha’sheretz Ha’romes Al Ha’aretz” – that we must not “defile” ourselves by eating creatures which crawl on the earth. The Sifra (Halachic Midrash on the Book of Vayikra) explains this verse as referring specifically to creatures which are produced on their own from refuse – such as spoiled food – as opposed to being produced from the mating of a male and female. The Rambam writes that the Torah used here the verb “Romes” (“crawl”), rather than the verb “Shoretz,” because “Romes” refers specifically to creatures produced through spontaneous generation. Thus, the Torah here introduces the prohibition eating such creatures.
The Ramban disputes the Rambam’s reading, demonstrating that the verb “Romes” is occasionally used even in reference to creatures which are produced through mating. Regardless, the Sefer Ha’hinuch follows the Rambam’s understanding of this verse as referring specifically to creatures produced through spontaneous generation.
This prohibition, of course, applies in all times and places, and to both males and females. One who intentionally eats a whole creature (“Beriya”) belonging to such a species is liable to Malkut regardless of its size. If the creature one consumes is not whole, then he is liable to Malkut only if he eats the quantity of Ke’zayit.