How to stop snails and spiders getting into plastic storage boxes?

[enginestar]

I have large plastic container boxes in the garden. These are great for storing things.

Problem: snails! And to a lesser extent spiders.
They leave what I assume is snail excrement.

How do I keep them out of the plastic storage containers? How do they get in? The boxes aren't air tight, but designed to stop water getting in. The size of the snails has got me confused, there's no way they can get in - do they get in when really small? But then... how do they feed to them get bigger?

Thanks.

 

[DirtMechanic]

Maybe a cloth or foam strip glued about the lip of the lid to seal the air gap.

 

[Oliver Buckle]

Perhaps you should re-define them as useful storage boxes/snail traps
Seriously, it is good to have the snails where you can find them and get rid of them rather than eating your garden. Spiders I never mind, I would rather have them than what they eat.

 

[garden man]

Spiders I don't mind too much but you're right, so many snails in the plastic gardening stage containers!!
Some copper tape around the outside about 2" down from the lid and also a strip around the lid. Copper does not kill the snails but gives them a bit of an electric shock, thus deterring them. Remember though, their excrement is excellent plant food so you might want to harvest it instead for all those lovely Spring flowers.

 

[Sheal]

Are the eggs of the snails/spiders already in the boxes, possibly introduced by the items in there? Fiddly - but cling film might work if you create a seal with it.