How can the Melocho of דש – Extraction – apply to the Murex snail?

Some have objected to the Murex as a candidate for the חלזון of תכלת , as follows:

• The amount of dye extracted from one murex snail is minimal.
• The Gemara (cited in the previous question) assumes that one can be culpable of transgressing the Melocho of Dosh – extracting liquid, when extracting the dye from one .חלזון
• The Rambam (above) seems to state that the minimum amount of liquid needed to be extracted to be culpable for Dosh is a גרוגרת – the bulk of a dried fig. Since the amount of dye normally extracted from a murex is presumably less than that, the murex cannot be the חלזון of .תכלת

There are a number of flaws in this argument:

It is not at all clear from the Gemara that it is speaking specifically about extracting dye from one single חלזון . The Gemara is not discussing the שיעור for the Melocho. In principle, it may very well be that more than one חלזון is necessary for the שיעור to be reached.

Furthermore, the assumption that the minimum amount for the Melocho of Dosh is a גרוגרת is also far from clear. In fact the Yerushalmi says this שיעור only in regard to food 194.

The Raavad explicitly states that the שיעור changes based on the type of liquid we are discussing. He compares this to the Melocho of -הוצאה carrying, where the amount one needs to carry to be culpable changes from item to item, based on how much is considered a useful amount 195. Hence, it would be logical to say, that when discussing a dye that every single drop was considered priceless, the שיעור would be much less than a גרוגרת – perhaps even as little as one drop.

Pliny: “…the Tyrian dibapha 131, which could not be bought for even one thousand denarii per pound.”196

Theopompus: “Purple for dyes fetched its weight in silver at Colophon.”197

Even the Rambam, that does require the שיעור of גרוגרת for extraction of blood, is only speaking about a wound. It is likely, as explained, that even the Rambam would agree that in a case where the blood is intrinsically valuable, the שיעור will be much smaller 198.

Bottom Line: The Melocho and Shiur of דישה certainly apply to the Murex, where each drop of dye was priceless.