This is a close-up of a back leg of a Black widow spider. As you can see, it's covered with little bristles. These are used for combing large swaths of silk from their spinnerets and tossing it quickly over a victim to ensnare it. They also use these combs in the building of their webs.

There are over 2000 species in the Comb-Footed spider family (Theridiidae), found world-wide. Most are fairly harmless, with exception of the Widow spiders, some of which are among the most venomous in the world.

These spiders are also known as cobweb or tangleweb spiders because they create dense webs of disorganized, sticky threads to capture their victims. These webs are enlarged over time and a single touch will alert the lurking spider.

Did you know that spiders have up to four types of silk? They can place these strands at will depending on what is needed at the moment! Each type of silk comes out of its own spinnerets, and the link here will show you a magnified image of a spider's spnnerets with silk strands being pulled out!

If you would like to know more about Comb-Footed spiders, Wiki has a nice page here: Wiki: Theridiidae. For more information about spider silk, this is a wonderful source! Spider Silk