It’s pretty interesting how volume covers each of the main four is on have their own specific animal on them. At first it seems like nothing more than an artistic choice but it could actually have more to it than that as it helps with the characterization of each of the main 4
Morena plays a similar role to the ant queen,both are able to spawn an army of extremely dangerous people/creatures capable of using nen and are also capable of starting their own faction. They also both stay in their hideouts producing more warriors 
