Why the enormous, globular (phragmotic) head on this termite soldier? Soldiers protect the hive primarily against ant incursions. The mandibles are obvious. But the large head comes into effect as stoppers. They can literally plug their head into an opening and block unwanted entry.
I've got a large cranium. Maybe I'm phragmotic. Maybe I'll style myself as a 'human soldier,' a member of that elite caste of humans capable of jamming his head into openings to prevent burglaries and home invasions. I'll try it out the next time an unwanted solicitor tricks me in to opening my front door.
Photo source: Rundstedt B. Rovillos