A Spider Can Smell Anything It Touches.
Spiders learn about the world around them through their senses, including their sense of smell. While a spider does not have a nose, it does have a way of identifying the scent of other things, especially prey, through chemical receptors that are located on the spider's legs. This is why spiders sometimes release the prey insects that have become caught in their webs. Through touch, the spider can identify whether the prey is edible and safe to eat or whether it is something like a leaf that has simply blown into the web.
Hairy Legs Help Spiders Smell
Not a lot is known about spiders' sense of smell, except that they smell through touching things with their legs and all spiders possess a sense of smell. Spiders have specialized hairs along their legs that allow them to smell the objects they touch by interpreting the chemicals that make up the scent. These special hairs allow the spider to identify prey insects, other insects and even other spiders. This means that if a spider is crawling on you, then it can also smell you, thanks to its hairy legs that will be touching your skin.