One of the most annoying mobs in my opinion, the spider runs and attacks the player at a much quicker pace (pauses a lot - take advantage of that!), almost always requiring an obstacle to get away. The spider can ruin the life quest without a spear.
Its special ability is to trap players for 2–3 seconds allowing the spider to catch up and deal massive damage. The time between webbing seems to be random. However, it can only trap you if you are relatively close to it (sword range close). The longer a fight with one, the more dangerous it is. Make sure when fighting a spider to have at least a wooden sword. Fighting spiders can be deadly if there are other hostile mobs nearby.
The spider gives 2 thread, which is used to make bandages, earmuffs, coat, and many other useful items. The Spider doesn't do as much damage as the wolf, and it has much less hp then the wolf, plus you can kill a spider with only a wooden sword, even if the spider goes on top of you, meaning a wolf is stronger.
An emergency way to escape a spider is to put an obstacle between you, forcing the A.I. to de-aggro and leave. This tactic also lets you hit a spider with a spear behind a wall without taking damage (if you stay there it continues to aggro).
If you're wearing the Lava Helmet you are completely invulnerable to spiders attacks!
Try to avoid wolves when in a spider fight, because they can trap you and may even kill you with the help of the wolf.
If there is a large group of them, avoid at all costs. If you really need the thread, try lure one away so you can fight 1v1.
The spider was added in the 'Attack If You Dare' update, being the 3rd ever mob to be added.