For people losing snakes, here’s some advice:

1. Visiting Friends
On some of your friend visits, you hear a hissing sound. And on some visits you hear an extra “hiss” – the same hiss you hear when snakes are spawning in your own town. But in a friend’s town, it means that snakes are released from your inventory – and that all the snakes you see in your friend’s towns are all yours. If you have a Whacking License, you’re able to tap on them – and that’s in addition to the snakes you’re able to tap with your license. Although you may get some eggs back, you’ll get most of your snakes as well as the 5 or 10 you’re allowed to tap. Also, tap on them all in one visit and don’t go back in again, because if you lost them once in that town, you’re almost guaranteed to lose them again.

This really means, if you don’t have a Whacking License yet, it’s better to hold off on visiting friends until you do.

2. Lisa’s Task
For Lisa’s β€œRelease Snakes from Another Town” task, if a friend chooses your town it removes snakes from your inventory (it seems to be 5 rather than 3). BUT although you lose 5 snakes, there are also 5 new snakes are available to be tapped in your town. Again, although you may get some eggs back, you can still re-tap these snakes and put them back in your inventory.

That also means that if you really want to be a good neighbor, send Lisa to the Other Springfield to release the snakes!

Thanks to kD1909 for this.