Snails are of two types, land snails and sea snails. Land snails come under the same heading as “insects and vermin” which have no blood that flows. Sea snails come under the heading of shellfish, which are sea animals.
In al-Mawsoo’ah al-‘Arabiyyah al-‘Aalamiyyah it says:
The snail is a invertebrate sea animal, and it is a kind of shellfish. Most snails have an external shell; some snails have a small flat shell above or under the skin, but most do not have a shell at all.
Land snails have a pair of antennae, with an eye at the end of the longer antenna. The large sand snail is regarded as a harmful pest, because it has a voracious appetite for plants. Its length reaches 10 cm. End quote.
With regard to the ruling on eating snails:
1. Land snails come under the ruling on eating “insects”. The majority of scholars are of the view that it is haraam. Al-Nawawi (may Allaah have mercy on him) said in al-Majmoo’ (9/16): The view of the scholars concerning land insects … our view is that it is haraam. This was the view of Abu Haneefah, Ahmad and Dawood. Maalik said: it is halaal. End quote.
Ibn Hazm (may Allaah have mercy on him) said:
It is not permissible to eat land snails or any other “insects and vermin”, such as geckos, cockroaches, ants, bees, flies, wasps, worms, lice, fleas, bedbugs, mosquitoes or anything else of that type, because Allaah says (interpretation of the meaning): “Forbidden to you (for food) are: Al‑Maitah (the dead animals)” and “unless you are able to slaughter it (before its death)” [al-Maa’idah 5:3]. And there is sound proof that slaughter can only be done in the neck or upper chest, so if it is not possible to slaughter it, then there is no way one can eat it unless it is dead i.e., not slaughtered properly, so it is haraam. End quote.
Al-Muhalla (6/76, 77).
The Maalikis did not stipulate that a creature which has no flowing blood should be slaughtered, rather they included it under the same ruling as locusts, and its slaughter is by boiling, roasting, or piercing it with a stick or needle until it is dead, whilst saying the name of Allaah over it.
In al-Mudawwanah (1/542) it says:
Maalik was asked about something in the Maghreb (North Africa) which is called a snail, that is found in the desert on the trees – can it be eaten? He said: I think it is like the locust. If it is taken alive and boiled or roasted, I do not think there is anything wrong with eating it, but if it is found dead, it should not be eaten. End quote.
In al-Muntaqa Sharh al-Muwatta’ (3/110) by Abu’l-Waleed al-Baaji (may Allaah have mercy on him) it says:
If that is proven, then the ruling on snails is the same as the ruling on locusts. Maalik said its slaughtering is by boiling or being pierced with a stick or needle until it dies, and the name of Allaah should be mentioned whilst doing so, as it is mentioned when cutting off the heads of locusts. End quote.
2. Sea snails are halaal, because of the general permission with regard to eating seafood. Allaah says (interpretation of the meaning):
“Lawful to you is (the pursuit of) water game and its use for food — for the benefit of yourselves and those who travel”
al-Bukhaari narrated that ‘Umar ibn al-Khattaab (may Allaah be pleased with him) said: “Water game means what is hunted, and its food is what the sea throws out (onto the shore).”
al-Bukhaari narrated from Shurayh, the companion of the Prophet (peace and blessings of Allaah be upon him), that he said: “Everything in the sea is madhbooh (slaughtered).”
But we have not seen any hadeeth which suggests that the Prophet (peace and blessings of Allaah be upon him) ate snails.
To sum up:
The permissibly of eating snails applies to both types, both land and sea snails. If they are cooked alive there is nothing wrong with that, because land snails have no blood so that it might be said that they must be slaughtered properly and the blood extracted, and sea snails come under the general permissibility of sea game and food.
And Allaah knows best.