How do some T's differentiate prey items?

[Bread]

I understand T's have poor eyesight and hunt by vibration via the hairs on there bodies/legs, but how do they differentiate prey items from non-prey?

I ask because I've been watching my Balfouri's tonight, and they were literally walking on top of one another and the guy at the bottom doesn't even flinch?
If i drop something in with any other T BOOM! they go straight for the disturbance?

 

[MetalMan2004]

Its baffling to me as well. Add to that the fact that some Ts are picky eaters. How do they know that you dropped a cricket in front of them and not a roach?

 

[Envoirment]

Their hairs are also able to "taste"/"smell" via chemoreceptors - so are able to distinguish between different prey items and other tarantulas that way. There's not been much if any research done into pheromones of tarantulas, but it is likey they have some sort of chemical signature to distinguish themselves from prey items. Not to mention that each species is different. A lot of tarantula species would happily cannibalise or attack each other (even if mating!) and there's only a small number of species known that would tolerate a communal set up (even then cannibalising sometimes takes place if not set up right).