the flag [biol.] I consider misleading - the term is not specially used just here.

predacious I consider by far the most common spelling, in my experience, but predaceous does exist (though it is the second choice of all online dictionaries consulted that had the alternative at all)
Googling has a different picture with the -eous version getting double the hits of the -ious version - though many of these are dictionary entries of the type "difficult words"

On the other hand, there appears to be a preference for the -ious form in GB, here the relationships are switched

what to flag it?
I'd say either not at all, or [alternative spelling]
and don't consider it worthy of its own entry

supported as an addition, not as an entry in its own right