Is a Snail an Insect? No — Here Is What It Actually Is

No. A snail is a mollusc, and insects are arthropods — two different phyla. In terms of relatedness, a snail sits closer to an octopus, a clam or an oyster than to any beetle, ant or fly in your garden.

The comparison that settles it

What a snail actually is

Phylum Mollusca → class Gastropoda.

Molluscs are one of the largest groups of animals on earth: slugs, snails, clams, mussels, oysters, squid, cuttlefish and octopus are all in it. Gastropods — “stomach-foot” — are the biggest class within that, with roughly 40,000 or more species living in the sea, in fresh water and on land.

What makes a gastropod a gastropod:

• Movement on a single muscular foot, on a layer of secreted mucus
• A radula, a ribbon covered in thousands of microscopic teeth used to rasp food
• A mantle, the tissue that secretes the shell
• Torsion during larval development, which rotates the body so the gills and anus end up over the head — a genuinely strange feature nothing in the insect world does

“Bug” is a separate question

Strictly, a true bug is an insect of the order Hemiptera — aphids, shield bugs, cicadas, leafhoppers — with piercing-sucking mouthparts. A beetle is not a true bug. A snail is not even in the running.

In everyday speech “bug” just means “small creeping thing”, and calling a snail one hurts nobody. It stops being harmless the moment you buy something to spray.

Why the distinction has teeth

What actually works on molluscs:

• Ferric phosphate pellets — a molluscicide, and much safer around pets and wildlife than the old metaldehyde products, which are now banned outdoors in several countries
• Phasmarhabditis nematodes, watered onto the soil — a parasitic nematode specific to slugs, and one of the few controls that reaches the ones feeding underground
• Hand collection at night with a torch, after rain — still the most effective single method
• Beer traps, sunk to the rim
• Predators: frogs, toads, hedgehogs, slow-worms, thrushes and ground beetles
• Watering in the morning, so the surface is dry when they are active

A few things a snail has that no insect does

• A radula with thousands of teeth on a conveyor-belt ribbon, continuously replaced.
• A shell that grows with the animal rather than being moulted — which is why a snail shell has growth lines, like a tree.
• Eyes on stalks, on the tips of the upper tentacles in land snails, retractable into the head.
• Blue-ish blood, because the oxygen carrier is copper-based haemocyanin rather than iron-based haemoglobin.
• Hermaphroditism — most land snails are both sexes at once, and two snails meeting can both end up laying eggs. Which is a large part of why there are so many of them.