In my world there is a trading city in the middle of a vast stretch of wild, untamed forest. It was built to serve as an in-between for merchants as there is a peaceful kingdom both north and south of it. The city is on the banks of a north-south flowing river.
My giant spiders have evolved over the last million years in several different branches. The main branch is the giant Wood Spider. The second (and why there needs to be a safe in-between for trade) is the giant Water Spider. The one I am dealing with is a minor branch, the giant Flying Spider.
They don't actually fly, but more like glide between trees like Flying Squirrels. They hunt by swooping out of the air and grabbing whatever they are hunting (anything from Giant Wood Spiders to Humans and Wildlife like deer).
1.) How might these three extremely different species of giant Spider evolve to hunt one another within the confines of a single forest the approximate size of the Sahara Desert?
2.) Is the evolution of a "gliding" arachnid possible? If so how could this happen.
For the purposes of this question use the Jba Fofi as a model and work from there. Make sure the spiders are agile and deadly as they have to fight my town and pose a threat.
While I don't want to invalidate existing answers, I feel the need to mention that answers should not use extreme handwavium and should have some base in a precedent. No magic or "it just is because it is" answers please. Thanks :)