Nicaragua is home to many exotic animals; however, which animal you may be close to depends on where you want to live. I live on the Pacific Coast which is very dry and seems to be home to many animals that would live in arid climates. While humidity is still high (which breeds all of the fun insects), we also have the joys of scorpions, snakes, ants, iguanas and frogs.
I've been stung several times by the scorpions, and while they are unpleasant creatures, the ones we have here are not too poisonous. I have never seen a poisonous spider. The creatures that bother me the most are the mosquitos and ants. We have a lot of varieties.
I've had dengue once (same as West Nile Virus in the U.S.). It is carried by mosquitos, and there is no medication for it. You just have to drink a lot of fluids and deal with the pain in your bones.
You don't have to worry about the big ants. They are harmless. The little black ants bite hard and leave a toxin that itches worse than a mosquito bite. It makes gardening very challenging!