Marcia... You can adjust the size of the hole if you need to. I have mine under my awning of my house so predators would have a really hard time getting to them... so far so good. We really don't have too many snakes etc. here. The only thing I have to deal with is I have occasionally had wasps build nests in them after the birds leave. I just take the jug down and throw it way in that case.
TY Vickie... a snake would have to crawl up the side of my house and across the supports of my awing to get into ours... not saying one couldn't if it really had the desire though!! LOL