Anything that can climb onto the top of your house can come down the plumbing vent pipe...frogs, snakes, bugs, etc. If they come into your bathroom and choose the shower the larger stuff, e.g. frogs & snakes, can't get past the drain gratting. But the bugs can. The frogs and snakes can get into the how through the toilet though. Had our first scorpion in the house this summer, Coweta area. May have hitched a ride with one of the dogs. We have the house sprayed for bugs now, every month, mainly due to the tremendous number of spiders this year. The yard is full of every spider you can immagine, no tarantilas yet thank goodness. Unfortunatly we are overrun with black widows. Anything outside that you need to pick up we turn over first! And the spider in your work boots. We've gotten into the habit of stepping on our shoes to smash any spiders in them prior to putting the shoes on. Very sad deal man.
