Shoot the actual body of the snail! Not the shell. The shell is like a plate of armor. Once you shoot it once with a dart it will go into its shell. Shoot from behind under the shell at its butt. Only eats vegetable cake! Once tamed you can harvest its slime as cementing paste!
Starve taming doesn't work too well for 2 reasons
1. It's food bar may be small, so it may start losing health before it even gets close to tame time.
2. The cool down gap for eating cake, means that you need to factor in the eating time.
Hope this helps