A simple experiment folks!
1. Invest in one pack of slug nematodes.
2. Collect some slugs.
3. Mix nematodes to the label recomended dilution.
4. Obtain a small propagator and add about 3 cms of moist soil to the base.
5. Place slugs in the propagator with a few lettuce leaves.
6. Drench the slugs and the compost in the nematode solution
7. Close the propagator lid.
8. Observe the slugs on a daily basis
9. Ask for your money back on the nematodes if you are not impressed by the result (or lack of it!)

QED!