We are based in the countryside, about 16km outside Chiang Rai city. It is the countryside (yes, I've said it again... to let it sink in a little), not the city. As such, we are surrounded by trees, forests, streams, hills, fields, and all other things natural to the countryside. In this setting, animals live, of all shapes, sizes, numbers, colours, and degrees of cuteness/annoyance/scariness/danger.
Animals range from: dogs; cats; geckos; ants; spiders; mosquitoes; mice; rats; cows, horses; birds; beetles; snakes; fish; and multitude of insects not already mentioned. Some you'll see every day, some you may never see during your entire stay (rats and snakes are a rarity, but they do turn up from time to time).
Certain animals appear at specific times of the year, for instance: although ants are around all year, they will appear more frequently during rainy season (or before rain storms arrive); during May-June, for 2-3 weeks, there is a particular flying ant which appears after dark, attracted by lights, dying in the hundreds and leaving the remains to be taken away by the ants.
How does this affect you, and the animals?
Well, hopefully it doesn't negatively - all the animals will be more scared of you than you of them. What it does mean though, is that you take precautions for comfort, and occasionally safety. For instance, always keep the mosquito screen doors and windows shut. If the light is starting to attract insects, turn it off before you get inundated. Everything that dies inside your room, as well as half-eaten snacks or opened cans of soft drinks, will attract ants. We can do nothing about this, and even if we were willing to exterminate everything for your added comfort, we don't wish to do so - it is for you to adapt to our environment, not us who should adapt to you.
Generally if you leave the animals alone, keep your living area clean, and close the screen windows/doors, you should have minimal problems. Please do not resort to an early volunteer's mantra - "I'm American - we kill it first, then find out if it was dangerous!", as he wiped the remains of a spider off his boot...