An eil kamtza is a type of locust. The word kamtza in Aramaic means locust, and the expression eil kamtza – a “ram locust” – probably refers to the fact that this particular type of locust had a head and antennae that appeared similar to ram’s horns (in many languages we find that beetles and insects are called by names of larger animals, e.g. the Hebrew word for a lady bug is parat Moshe Rabbeinu – Moses’ cow).
The Torah lists a number of locusts that are tahor – they are kosher and permissible to eat (see 11:21-22). Since the Torah not only offers bodily indications of kashrut, but also gives the names of the locusts that are kosher, the Sages insisted that locusts could only be identified as kosher if there were additional signs that they fell into a kosher category. In many cases there was also an existing tradition with regard to their status. From its description in the Talmud, it appears that the eil kamtza had a different appearance than other kosher locusts, which is why there was a specific need for testimony that would establish its kashrut.
Yosei ben Yo’ezer ish Tzereida was the first head of the pairs of scholars who are mentioned at the beginning of Massekhet Avot, a student of Antigonos ish Sokho. At that time, scholars were not given titles and were simply called by their names. According to the Talmud, Yosei ben Yo’ezer, who was a kohen, lived during the period when the Jewish leadership in Jerusalem was made up of Hellenists. He was put to death by his nephew Alcimus, who was an evil kohen, and died a martyr’s death.
He was known as the ḥasid she-bakehuna – the righteous among the priests – because he was particularly strict about issues of ritual purity. It was he who instituted the Rabbinic ordinance declaring the lands of the Diaspora to be considered ritually defiled. Although he was known for his strict positions in this area of halakha, in other fields he was known to be lenient – so much so that he is sometimes referred to as Yosei sharya – “Yosei the Permissive.”