When it comes to pest species we spend a lot of time thinking about how they forage. Usually pest species cause most of their problems through what they eat. This generates a lot of research on either finding out what makes them stop eating something (to protect what they are eating) or finding out what makes them start eating (to get them to eat toxic baits). One such pest species is the wool-digesting carpet beetle (Anthrenocerus australis) which is one of the few organisms that can easily digest keratin, the main wool protein. Carpets are normally fairly resilient to our invertebrate friends but an infestation of these beetles will soon have your expensive wool carpet looking very shabby. Recent research suggests that the chemical propiconazole gives protection against the wool-eating beetle but it was not clear whether this is because the chemical is toxic to the beetle, and they learn not to eat the wool, or if the chemical repels the beetle, perhaps through odour, so that they will not eat the wool.
As has become clear to me lately, Tolkien brought a lot of biology into his works. Does he have anything to say about food aversion behavior. Of course he does! Tolkien doesn’t tend to talk a lot about food in his books. There are few descriptions of the various feasts the characters attend. But Tolkien understood that food is important, especially for Sam and Frodo and their journey into the Land of Shadow where it is a constant concern. Tolkien also demonstrates that he had an understanding of the different types of repellency. For example, Pippin and Merry are captured by orcs and are taken towards Isengard.
“There [Pippin] lay for a while, fighting with despair. His head swam, but from the heat in his body he guessed that he had been given another draught. An Orc stooped over him, and flung him some bread and a strip of raw dried flesh. He ate the stale grey bread hungrily, but not the meat. He was famished but not yet so famished as to eat flesh flung to him by an Orc, the flesh of he dared not guess what creature.”
Without even tasting the food Pippin is repelled. The likely origin of the meat, the smell, the appearance are enough to stop Pippin from attempting to eat, despite the fact that the hobbit is incredibly hungry. One type of food that Tolkien did write a great deal about was lembas, an elvish waybread (in fact the supplies of lembas carried by the fellowship were probably as important to the success of ring quest as anything else!). This highly nutritious ‘biscuit’ was also very tasty. Even Gimli, with his general dwarven dustrust of elves, was moved to say that lembas was “better than the honey-cakes of the Beornings, and that is great praise, for the Beornings are the best bakers that I know of.” However, when Gollum is offered lembas by Frodo and Sam as they struggle through the barren Brown Lands we find that not everyone approves.
“At the word hungry a greenish light was kindled in Gollum’s pale eyes, and they seemed to protrude further than ever from his thin sickly face. For a moment he relapsed into his old Gollum-manner. ‘We are famisshed, yes famisshed we are. precious,’ he said. `What is it they eats? Have they nice fisshes? ‘ His tongue lolled out between his sharp yellow teeth. licking his colourless lips.
`No, we have got no fish,’ said Frodo. `We have only got this’ – he held up a wafer of lembas – ‘and water, if the water here is fit to drink.’
`Yess, yess, nice water,’ said Gollum. `Drink it, drink it, while we can! But what is it they’ve got, precious? Is it crunchable? Is it tasty? ‘
Frodo broke off a portion of a wafer and handed it to him on its leaf-wrapping. Gollum sniffed at the leaf and his face changed: a spasm of disgust came over it, and a hint of his old malice. `Sméagol smells it! ‘ he said. `Leaves out of the elf-country, gah! They stinks. He climbed in those trees, and he couldn’t wash the smell off his hands, my nice hands.’ Dropping the leaf, he took a corner of the lembas and nibbled it. He spat, and a fit of coughing shook him.
`Ach! No! ‘ he spluttered. `You try to choke poor Sméagol. Dust and ashes, he can’t eat that. He must starve. But Sméagol doesn’t mind. Nice hobbits! Sméagol has promised. He will starve. He can’t eat hobbits’ food. He will starve. Poor thin Sméagol! ‘”
Gollum, despite misgivings about the elvish taint to the food, is willing to try lembas but quickly finds it to be toxic to his system. Gollum doesn’t try to eat the hobbits’ food again (even later when it is a rabbit that Sam cooks up). So we have Pippin being repelled from orcan food simply by its dire smell and dubious look and Gollum from elvish food because it causes a reaction when he tries it. So are the carpet beetles Pippins or Gollums when it comes to propoconazole on wool?
Matt Sunderland and Rob Cruickshank (Lincoln University) have just published their findings in the Journal of Insect Behaviour. Matt and Rob set up several experiments with carpet beetles and propoconazole. One experiment placed a beetle in a Y tube where they could choose to approach a chamber with wool and propoconazole or one with just wool. The beetles did this equally. Another experiment placed beetles in a petri dish with half of the surface covered in propoconazole and the other with nothing. The beetle spent similar amounts of time on each surface. Carpet beetle larvae were exposed to propoconazole by it being dabbed onto their skin. This had no effect on them as larvae or their feeding preferences. It was only in experiments where the beetles ingested wool with propoconazole on it that the aversion arose. So the carpet beetles are not like Pippin with an inbuilt aversion to the chemical that they can detect before eating it. They are more like Gollums, willing to try the treated wool but suffering a reaction to the chemical from which they learn not to eat anymore.