The Torah lists eight sheratzim (creeping creatures) all of whom will render someone who touches them to be tameh (ritually defiled), if they are dead – see Sefer Vayikra 11:29-30. In Masechet Menahot (daf, or page 29a) the Sages taught that although their names are specified in the Torah, even Moshe was unable to identify each of them definitively. The Maharsha explains that this is because there are many such species and the differences between them are relatively small, to the extent that identifying them is difficult.
Even the broad term sheretz is subject to different interpretations. In his commentary on the Torah, Rashi suggests that this is a term that encompasses all fine, small animals that crawl on the ground. The Ramban quotes Onkelos as explaining that the fact that these animals are constantly in movement is what gives them this distinct name.
The Mishnah on today’s daf discusses those animals whose skin is considered to be flesh, i.e., it is soft and tender, so that with regard to the laws of ritual defilement they are treated like flesh. Such creatures include, for example, the skin of human beings, skin of the domestic pig, the skin of the hump of a young camel, and the skin of the head of a young calf. Rabbi Yohanan ben Nuri includes all eight of the sheratzim mentioned above, but the Tanna Kamma (=first) limits this rule to four of them – the anakah, the ko’ah, the leta’ah and the homet.
As noted above, we cannot be certain of the identification of these animals. Nevertheless, most of the commentaries agree that they are reptiles. Common identification suggests that –