User blog comment:Kogath/Monster Hunter 4 Ultimate for the Nintendo 3DS/@comment-6050823-20150407034406

You guys remember that post I made about the Magalas below? Well, I was completely wrong about it though it shades a mystery that might've been plaguing people. It actually talks about why Shagaru Magala claim territories.

Shagaru Magala spread a mist of the virus around their territory to prevent Gore Magala from molting properly. Inside their mist is a new powerful strand of the virus that infects all creatures in their territory, eventually killing most of them. But there is something else in their virus... The virus contains their parasitic offspring, the Gore Magala. Magala reproduce asexually. Their offspring live in the host whether it is dead or alive though infected corpses act as nurseries for the babies. They get their nutrition and everything they need from their host. So Shagaru Magara fill the area with the deadly mist so they can claim a territory for themselves, prevent future rivals from appearing, and to bring forth the next generation of Magalas.

So basically as Pike said, Fungus Dragons!