This depends a great deal on what type of spider! Spiders are extremely diverse, and frankly, a lot of them are not particularly 'agile'... When I think of agility and reflexes, though, I tend to think of jumping spiders (salticidae) first thing. It's generally agreed that they have the best vision of any spider and can probably see in color-- they hunt by stalking and pouncing on prey, so they have to be very very quick and accurate. Some species can leap up to fifty times their body length. They're also somewhat hard to catch, because their vision and response times are so good :P
I'm not sure how to specifically quantify 'agility and reflexes', though. I can tell you that they are sufficiently agile and have quick enough reflexes to regularly catch and eat flies, leaf hoppers, other spiders, etc, but without more specific parameters I don't really know what kind of hard facts I can quote to support this?
Active hunting (non-web-weaving) spiders, in general, will tend to have better reflexes. This would include jumping spiders, wolf spiders, fishing spiders, and crab spiders. Wolf spiders also hunt visually, although their vision is probably not as good as jumping spiders. Fishing spiders place their front feet on the surface of a body of water, and sense by vibration when potential prey is passing underneath. They can catch aquatic insects and even small fish, so their reflexes have to be fast. Crab spiders hunt by sitting and waiting, often in flowers; they grab insects that come to collect nectar. This often includes bees, so you can imagine these spiders are very strong, fast, and have great reflexes to avoid getting stung to death.
Web-weaving spiders, in general, tend to be less agile, just because the web does so much of the work for them. Their vision tends to be quite poor and they navigate by touch, sensing prey by feeling vibrations in the web. While they can move very quickly and skilfully within the web, most web-spiders are pretty wobbly when you get them walking on a flat surface, because their bodies are not really designed for it. They still need to have enough agility and reflexes to avoid getting hurt by dangerous prey, like bees or ants that might get caught in the web, and to react quickly when they catch something so that it doesn't get away.
There's a lot of variation! In general I would say that spiders, as a whole, have excellent reflexes and many of them can be quite agile, but again, there's no standard unit of agility measurement so I dunno how to be more specific than that ;)
How good are their agility and Reflexes? State facts please..
