[Lewis Thomson (OP)]

Donald is curious about this conundrum

"Apparently, there is interspecies variation in the olfactory receptors, for example the smell of asparagus in urine.  Obviously, dogs and ants must have different receptors and sensitivity. Which species is the best at smell, or sight, or touch, or hearing, or taste based on density, sensitivity and variety of receptors?"

What do you think? Leave your answers in the comments below...

[Eternal Student]

Hi.

   It is an interesting question and thanks for submitting it.

   Regrettably I think it would take too much space here to list everything and all the contenders for animals with "the best senses".

    There's reasonable information in this article:
https://www.sciencefocus.com/nature/amazing-animal-super-senses/
    There's also hours of popular science videos about animals and their amazing senses.   This series was quite good, if you can still get hold of it  (I'm sorry but free access has timed out from this link):
https://www.bbc.co.uk/programmes/b04fhp70       "Super Senses:  The secret power of animals" by the BBC.

   There is endless amounts of information.

   Exactly as you stated,  there is considerable variation in sensory capabilities between species.    So it's not as simple as saying   "which species has the best sense of smell?",   some species are generally very good at odour detection,  e.g.  dogs,  but they can be quite oblivious or unaware of one type of molecule.   That might be a molecule that some other species uses as an important odour marker and that other species might be extremely sensitive to.   As such our presumed best overall sniffer  (the dog) is effectively "blind" to one odour that someone in the animal kingdom thinks is very important.    We also have a problem if we take one animal out of its natural environment and put them in some other.   For example, a dog can't smell very much at all when they are in water but a shark is a completely different thing and can smell blood in the water from a quarter-mile.

    I notice that you have been extremely precise and tried to specify some criteria you would use to determine which animal was overall "the best"...

...based on density, sensitivity and variety of receptors?

    However, even that is still difficult to answer.   How much importance do you want to put on each of those things?   For example, is the ability to detect electric fields so amazing that having that ability tops the score for "variety of receptors"?

    It's usually said that every animal is well adapted and it is often the very best it can be for the niche it occupies in the overall ecology.   It doesn't matter if its senses seem unimportant to another animal, they are important for this animal in this niche.

Best Wishes.

[Bored chemist]

"Which is the best animal has the best senses?"
The one which developed microscopes, radar and spectroscopy.