To attract insect or animal at a great distance powerful odours are necessary, such as our grosser senses can perceive.

Then the exploiters of the odorous substance hasten from afar off and from all directions.
If for purposes of study I require specimens of such insects as dissect dead bodies I expose a dead mole to the sunlight in a distant corner of my orchard.

As soon as the creature is swollen with the gases of putrefaction, and the fur commences to fall from the greenish skin, a host of insects arrive--Silphidae, Dermestes, Horn-beetles, and Necrophori--of which not a single specimen could ever be obtained in my garden or even in the neighbourhood without the use of such a bait.
They have been warned by the sense of smell, although far away in all directions, while I myself can escape from the stench by recoiling a few paces.

In comparison with their sense of smell mine is miserable; but in this case, both for me and for them, there is really what our language calls an odour.
I can do still better with the flower of the Serpent Arum (_Arum dracunculus_), so noteworthy both for its form and its incomparable stench.

Imagine a wide lanceolated blade of a vinous purple, some twenty inches in length, which is twisted at the base into an ovoid purse about the size of a hen's egg.