debz - keep missing you lol
The lower case letters apply to all the creatures when MS uses them generically. ...flew a firefly and a beetle.... When MS says Beetle he is writing about the creature whose name is Beetle and so on. They appear to be the mates of the named creatures but with the exception of Snail whose husband is also named Snail (p 14), we don't know any mate names. Elsewhere MS caps them when they maybe shouldn't be - p 73 an example with Dragonfly
As to how they knew the flying formation - good question.