The King Crabusses are the biggest and strongest species of Crabus that exist in the present, being "nerfed" versions of the Emperor Crabusses. Why did they evolve into these forms? In the past, the planets where they lived had more resources, allowing them to have forms that also required more resources to survive. As these started to decrease, the Emperor Crabusses needed to adapt into lighter forms, thus after millions of years they finally became King Crabusses.
They have "King" in their name because smaller Crabusses often tend to be close to groups of King Crabusses, as a way to be safer agaisnt predators. They commonly have a dark red / dark orange color scheme.
There has been recorded cases of some King Crabusses having more similitude with their primitive forms rather than their newer forms. They act like leaders of the King Crabusses, commonly being stronger and bigger than the others. This also means that like their predecessors they need more food in order to survive, thus making them more agressive.
If a King Crabus / a normal Crabus dies or gets harmed to the point of no return, King Crabusses will feast on them, with the main priority being the leaders / Emperor Crabusses.
The reason king crabusses are much less stronger than their predecessors is because of pollution. the more the air is polluted, the less oxygen there is in it, more oxygen = bigger lungs = bigger size and strength, so they evolved this way to not die from hypoxia.