Tarantula's have Chemo-receptors in their pedipalps and front legs that they use to sense their surroundings and food. Taste and smell would be their closest comparison to human senses. If we were talking about reptiles it would be like the tongue and jacobson's organ.
It's true, they have chemosensory organs on their legs and palps that let them "taste and smell". This is why you might get grabbed while working in the tank by a snoozing T that suddenly noticed a disturbance near it but you will only very, very rarely be bitten. The T grabs you and realises it's just some big ape and not food and lets go.