Do slugs eat insects

100% yes.

Until last night I assumed slugs only ate plants but I was wrong. Each night as I lose my dogs out the back to do their business I always notice huge Spiders on my White House walls. I dispatch the spiders as they crawl through the vented Windows.

Upon letting the dog back in I witnessed a slug eating the dead spider that was stuck to the wall. I took photos of it to prove. All that remained were the legs.

So there you go. Slugs are omnivore's.