OK, so ainulindalenya‘s post on Quenya insect orders got me thinking about Giant Eagle lice, and because I wanted to be able to sleep last night, I worked out whether they would present an issue for hobbits escaping Mordor.
TL;DR - Yes, yes they would.
Golden Eagles, which are big freaking eagles, harbour a common species of louse called Laemobothrion maximum (Scopoli), which, according to this paper, can get to be at least 10mm long. There may be larger eagle lice, but this is a nice round number.
Golden Eagles have a wingspan of about 7′8″, which is huge. But, Thorondor, the greatest of the Great Eagles, was reported to have a wingspan of 30 fathoms, or 180′, which is just plain silly, but I digress. Assuming everything scales proportionately between real eagles and Tolkien’s Great Eagles, and that Middle-earth had a higher atmospheric oxygen concentration than we do, in theory, Thorondor could have been home to feather lice that were roughly 12″ long.
Now, assuming that regular Giant Eagles are ~¾ the size of Thorondor, that would make their lice about 8″ long. For reference, Frodo was rumoured to be almost 4′ tall, and taller than most hobbits. Even still, Great Eagle feather lice would conceivably be the size of his thigh.
I’m no expert when it comes to eagle jockeying, but I would expect that with an injured hand, at least a mild state of shock, and the emotional and physical exhaustion that comes from saving the world from evil (after being at least partly consumed by said evil), having a louse the size of his thigh crawling across him would probably freak Frodo (and equally, Sam) right the hell out, and potentially cause him to fall off his eagle steed.
But, having the hero survive the quest into Mount Doom only to be killed by a wayward eagle louse would make for a pretty anti-climatic ending to an epic trilogy, so I don’t blame Tolkien for delousing his eagles. I guess.
Now to figure out which wood-boring beetles were responsible for chasing the Entwives away…