Falscale are large bugs that parasitize dragons in a most unusual way. You see, they take off a dragon's scales and take their place. There are two ways this could work:
A Falscale takes off a dragon scale, attaches it to their back (essentially grafting it to their own body), and then settles into the niche the scale once occupied
A Falscale removes and eats a dragon scale, settles into the scale's former location, then grows layers of protective chitin on its back. These extra layers will incorporate the consumed scale, therefore resulting in decent protection for parasite and host
I'm not sure which method is the most effective or feasible, but the idea is that Falscale will attack a dragon like a swarm of locusts, take the scales off the unfortunate victim, then take the scale's place on the dragon's body.
My question is therefore: Under What Conditions Could This Trait Develop?
In other words, what would it take to get a species of bugs that will attack dragons in swarms, remove its scales, and then take the place of said scales?
EDIT: Since it has been pointed out to me that I must explain my dragon's origins, I will do so now. Dragons in Alendyias are descended from lizards, which thanks to certain Enchantments gained their current from. More on that can be found here. Because of this, Falscale are almost certainly going to evolve from bug parasites and use Mimicry to achieve the desired effect (ie. replacing dragonscales).
To make things clear, Falscale use the two methods specified above to not only remove scales, but to incorporate them into their own bodies for additional protection.
The 1st method basically grafts a scale onto the Falscale's back, protecting it after it embeds itself into the skin so it can leech nutrients and oxygen from its host's blood. The 2nd method is more complicated; the Falscale removes a scale, eats it, and incorporates the scale into the chitin on its back, essentially forming a protective plate atop the embedded parasite. Either way, you get parasitic armor.
"But, what's the benefit?" This is the twisted genius of this strategy; after the swarm has landed and settled in, it has essentially become the dragon's skin. Would you tear your skin off? No, that's ridiculous-and thus the parasite assures it will not be removed.
Additionally, thanks to the Mimicry Enchantment, it's actually perfectly feasible for Falscale to do what they do; all they're doing is replicating the consumed scale (or the removed scale's attachment to the body). And because the Mimicry enchantment is so integral to dragons, it's not exactly hard for the Falscale to gain it from their host.