SMELL FIELDWORK AND EXPERIMENTS 99 



birds, and so on. The corpses are used as food stores for the 

 larvae which will hatch from the eggs which are laid on or 

 near the body; but before depositing the eggs, the beetles 

 — often in numbers — excavate a "grave" by scraping away 

 the soil from underneath the corpse. This being done, a pair 

 will usually take possession and lay their eggs. However, it 

 is with the location of the carrion that we are concerned. 

 The beetles themselves will find a suitable dead animal 

 from a long way off. At times they will use their delicate 

 powers of scent when on the wing, or they may travel over- 

 land. In either case, their smelling abilities must be most 

 efficient. 



As I have already stated, scents are used by some insects 

 for defensive purposes, and good examples of this can be 

 observed in the ladybirds and those plant pests known as 

 "shield bugs". These both excrete an offensive smelling 

 liquid (which even our own noses can detect) and this serves 

 as a protective warning to predators. 



Fishes 



In fishes the sense of smell in some families is marked ; and 

 these fish are either attracted or repelled by odours diffused 

 through the water. Anglers have known this for hundreds 

 of years, and even today anglers who go in for coarse-fishing 

 often scent their bread paste bait with aniseed in the hope 

 of attracting fish more easily. Many put far too much aniseed 

 or other sweet-smelling substances in their bait and so defeat 

 their own object. Only a very little is required to make a 

 scented bait more attractive than unscented. Aquarium 

 fishes may be used to test this, and if small pellets of plain 

 paste are fed to the fish in addition to some that are scented, 

 the fish will go first for those which smell. Care must be taken 

 in such experiments to see that the unscented pellets are 

 dropped into the tank well away from the place where the 

 scented ones are put. The plain pellets must be made up 

 before those which have the scented substances added, or it 

 will be found that one's hands — even after washing — will 

 carry some scent, thus spoiling the experiment. 



Sharks are, perhaps, the fishes that can smell most keenly, 



