Cobweb

The cobweb is a new item introduced in Beta 1.5. It was previously found in the terrain.png file, but had no block ID assigned to it. It is not generated or crafted in any way. Current thoughts are that spiders will nest in it, shoot the web at you to slow you down, or drop it as loot.

Moving into a cobweb limits your movement abilities. When you are "inside" the cobweb, you will move at a speed equal to about 15% of the normal walking speed. Additionally, jumping will vibrate the player, akin to jumping in a 2 block high space. Unlike water, however, falling into a cobweb will not prevent fall damage, although it will be delayed until you make contact with the ground.

It currently has no use, placing it in a crafting table has no effect, nor is it craftable from String.

History
Notch originally planned for spiders to produce webs.

Trivia

 * Cobweb blocks can be used as air pockets in the same manner as Sugar Cane.
 * Cobwebs can be placed on cobwebs.
 * Items thrown on the cobweb are also slowed and will fall down after about 20 seconds.
 * A block of Sand or Gravel which falls or is shot into a cobweb, will slow down, then be destroyed and become a resource after about 4 seconds. Primed TNT seems to be not affected by this phenomenon, as it doesn't disappear and will eventually explode destroying the cobweb.
 * Animals that walk into the cobweb will slow down, even spiders.
 * Minecarts treat it as a solid block, like glass mixed with wool.
 * Players are unaffected by cobwebs when in a minecart, except when they are in the way of the cart. This allows creation of a mob-slowing tunnel that can be ridden through with ease, making safe rooms even safer.
 * Signs and paintings can be placed on cobwebs.
 * Ghasts will not see players in or behind cobwebs.
 * Cobwebs do not stop chests from being opened.
 * Jumping from as little as one block above a cobweb, onto it, will induce half of a heart in fall damage.
 * A shot Arrow cannot pass through cobwebs and will not slow down.
 * Any kind of mechanism (excluding Dispensers and Note Blocks) can not be placed on top of cobwebs.
 * Players are unable to jump while in a cobweb.
 * Cobwebs can be placed on Sugar Cane and in Water.
 * When falling into a cobweb, if a player gets into a minecart or boat before hitting the ground, they will not take the fall damage until they exit the cart/boat.
 * Cobwebs have proven to be useful particularly in water-filled moats 3 blocks in depth. Adding a layer of cobweb to the bottom of the moat will render any mob (or players) stuck. It is possible to get out (granted you will lose health from a near drowning experience) but most mobs will drown. This is a particularly efficient method of repelling creepers from hiding around the corner of your house entrance.
 * Cobwebs seem to not be able to make the terrain biome recognizable, confirmed on SMP, while riding a minecart falling into a cobweb with water below.
 * For example, the biome was a forest, which was supposed to make it rain, instead there was snow.
 * In SMP, the particles given off when breaking a cobweb may slow down whilst falling, as they appear before the cobweb block disappears. This also seems to cause them not to fly outwards, but just drop directly downwards after the cobweb disappears. This phenomenon only seems to happen if there is a considerable amount of lag on the server.
 * Placing cobwebs on ice will increase the slowing effect of the cobweb.
 * Cobwebs can be used as "quicksand", but it cannot suffocate the one who enters it. In 1.6.4 webs will suffocate players
 * As of 1.6.4, walking into a cobweb at head height will now suffocate the player. This is considered a bug though.