In order to defeat one without pumping a dozen cases of shotgun shells or a few boxes of magnum rounds into it is to equip the semi-automatic rifle with the thermal scope and pick off all parasites under the skin of the offending Plagas motel.
"It's a regenerator, n00b. Lol."
There is also a sub-species called the 'Iron Maiden' which has spikes.
You can tell when one is coming by their ragged laughing breath.
Can only be killed with a rifle rigged with a thermal scope.
That dude: I know man! Here, give me the controller, I'll kill it! Goddamn Regenerator bit my head off! DAMN!