There is a large variety of spider in RR, but very few specific description. What we know is that almost each of them is described as dangerous predator to players.
They are the largest order of arachnids and rank among the top monster in total species diversity in RR.
Spider are monsters from small to learge. But they all have in common to be air-breathing arthropods that have eight legs and fangs that can inject venom.
Anatomically, spiders body are usually into two parts, the cephalothorax and abdomen, and joined by a small, cylindrical pedicel. Other than that any color or size is possible.
They have a centralised nervous system. Means they can be affected by almost any type of magic.
Their abdomens bear appendages that extrude silk from up to six types of silk glands within their abdomen. Spider webs vary widely in size, shape and the amount of sticky thread used.
Their limb extend by hydraulic pressure, and not by muscle. They do not have antennae nor true jaw. In fact, spiders' guts are too narrow to take solids, and they liquidize their food by flooding it with digestive enzymes and grinding it.
A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration to co-operative hunting and food-sharing.
They are spiders all over the Continent. They adapt to almost any climate and places, except for the Sea. Other than that you can find them hunting outdoor or indoor.
First appearance indoor in the spider dungeon (v1c10). Then another large type outdoor in the Bar Khu Mountain range (v3c1), in Todeum (v12c7), Boss type spider in the Kramador dungeon (v15c4)
More to come
Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and some hunters show signs of intelligence in their choice of tactics and ability to develop new ones.
Special attack Edit
Fangs with venom
Trample and charge for the larger type
Various type of special attack/defense, depending of the subspecies (jumping, spiting poison, etc.)
Weak to fire
Weak to magic
If you have the adequate skills, they can be hunted for their silk or their venom, which can be very useful. For example, Spider silk provides a combination of lightness, strength and elasticity that is superior to that of any synthetic materials. For tailor, it should be tier 1 material.
Tori and vampires are known to have the power to summon spider with strong web producing skills (v12c7).
External source: Wikipedia