Tumat Sheratzim - impurity of crawling creatures
Please note that the term "Sheretz" refers to a "Crawling Creature," here limited to those which communicate impurity, and that the pluralization of "Sheretz" is "Sheratzim."Defining a "Sheretz"
A serpent is not a sheretz: Eruvin 13b; Keritot 4bCommunication of impurity from a sheretzBeyond the Laws
There was an aged student in Yavneh who could provide 150 reasons why a sheretz should be considered pure: Eruvin 13b