I know, then people starting talking about why they -can't- be right?
Besides we'd need a walking version of these, be it in their -trap door- tunnels (Like the radscorpion nest?) Or simply drawing them out into the open. How else would you combat them?
Gamgee: Whats implausible about what I said? The best way to combat Cazadores are to slow them down, obviously the spiders would have had to evolve a way of doing so.. they do -come- with a naturally sticky substance built in.. There is no need to reduce the debate into childishness or take it off topic.
Almost everything in new vegas seems to have evolved or mutated from an existing stock. Cazadors have mutated from tarantula hunters, the wasps that lay eggs in spiders. Or they share a great deal in common with. Deathclaws from experimentation/lizards ect. Most things don't seem to get new traits from the base species. Just enhanced and supremely powerful.
I can't see the spiders somehow magically developing poison resistance over night, or a sticky coating, and the worse offender is the sticky ball shooting. Maybe... like a line to catch prey, or drop a net from above which some spiders CAN do. Adds a sense of realism to the creature. Also I was using sarcasm to enhance my argument. Sorry if it came off as mean. As it is I can't see spiders adapting anything they already have to fight off cazadors. Hence evolution would make any existing species more proliferous in large colonies of eggs/young lings. Mother spiders being the largest and only the size of a medium dog. This way cazadors can't just wade into the colonies and expect to live, but at the same time anything passing by these webbed spires is ripe for hunting and being dragged back to the nest or even stupidly blundering into it for some loot.
We can even have some sub genus of the trap door spider live in a minefield around this place. The "hunters" of the colony that make sure to stay out of sight of Cazadors since they don't have the numbers to back themselves sup when outside of a colony. Once the spider colony get's to a certain size a chunk of population breaks off and goes out into the wasteland to look for another area/structure to infest.
So trap door spiders crossed with jumping spiders, and the swarmy nature of ants. Good god run away now.
Edit
You could design a whole mission around fending off an invasion of gigantic spiders looking to infest the town. The best option is have the cazador come in while the spiders are in a relatively vulnerable state without a base of operations, but then you have Cazadore in the town to deal with. The alternative is to try and fight back the infestation with human power.