Tzeida – Trapping a Chillazon on Shabbat
תנו רבנן: הצד חלזון והפוצעו אינו חייב אלא אחת (שבת ע”ה.)
The Rabbis taught: One who traps a ḥilazon and breaks its shell to remove its blood for the dye is liable to bring only one sin-offering (Shabbat 75a)
Clearly, the chillazon requires trapping. Due to the fact that the Murex trunculus – a slow moving snail – is ostensibly easily caught, there is concern that it fails to meet this criterion. To understand if trapping the Murex trunculus would, in fact, violate the biblical prohibition and the creature would therefore remain a candidate for the mysterious chillazon[source of Tekhelet dye], an investigation into the labor of trapping is required. Such an investigation requires examining the scientific nature of the specimen in question as well as that of the myriad other creatures mentioned in the Torah and Talmud that are said to either require the labor of trapping or, on the contrary, to be exempt from such labor.
(R. Mois Navon, Threads of Reason)
Click to read the full article: Ha-Zad Chillazon – Trapping the Murex trunculus
Catching the Murex is done today the same way as in ancient times. Baited baskets are lowered to the sea floor and after a few days they are collected, full of snails. The ancient Roman naturalist, Pliny the Elder put it this way: Baskets were “cast into the sea, and in them cockles are put as bait…. In this way, victims to their own greediness, they [the snails] are drawn to the surface hanging by their tongue.”