Humans have 10 hearts.

Spiders have 8 hearts.

Why do arachnids have 7 hearts? A total of eight would be the same as a spider, and nine would be halfway between human and spider. Why seven?

Not really a bug, but a curiosity. An extra heart wouldn't do much for gameplay, but would resolve the strange inconsistency.

technically you are not a spider but a type of arachnid so there is no inconsistency.

Or maybe instead reduce fall damage, the only real problem in having only 7 hearts is that it is really easy to die from fall damage while climbing IMHO.