Most years I'll see a few slugs and have some minor plant damage from them. Last year, dampest on record they say, brought forth more slugs than all the previous years put together! My plants were decimated, I was killing slugs wholesale, and still the next day I'd find half a dozen or more of the slimy critters ambling across the lawn in full daylight, bold as brass.
Afraid they would have bred an even larger army for this year I decided to try a more pro-active approach. I applied one packet of these nematodes at the start of April, probably rather more generously than required (you can't keep the stuff, so you may as well use it). You're supposed to re-apply every couple of months, but I have not done so.
I haven't seen one single slug this year whatsoever. :)
This might be coincidence, it has after all been quite dry. However, none of my plants have slug damage, not one sign of slimy trails, and this is now September. I have seen the usual number of snails, but these don't seem to cause the same scale of damage I see from slugs.
It's a fairly costly way to control garden pests, especially if you re-apply per the instructions. One rating star is knocked off to reflect this huge premium. I've used slug pellets before, which are enormously cheaper, but have never liked the damage they do to the other local wildlife. I'll definitely buy another packet of nematodes next spring.