An el kamtzah is a type of locust. The word kamtzah in Aramaic means locust, and the expression el kamtzah – 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 MosheRabbenu – Moses’ cow).
The Torah lists a number of locusts that are tahor – they are kosher and permissible to eat (see Vayikra 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 el kamtzah had a different appearance than other kosher locusts, which is why there was a specific need for testimony that would establish its kashrut.
Yossi ben Yo’ezer ish Tzreda was the first head of the pairs of scholars who are mentioned at the beginning of Masechet 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, Yossi 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 Alkiyos, who was an evil kohen, and died a martyr’s death.
He was known as the hasid she-bakehunah – 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 halakhah, in other fields he was known to be lenient – so much so that he is sometimes referred to Yossi sharya – “Yossi, the one who permits.”