This is a concept from 2007 but I never had gotten around to painting it.
The 'borer' is exclusively used by the megacorporation URSYN as an area denial and anti insurgency weapon; thousands may be seeded in key areas whereupon they can lie dormant for months.
Borers are activated when a person or unlucky animal steps on it; the borer will rapidly tunnel up the flesh of the victim and attempt to detonate in the cranium. Even in the event that it doesn't reach the head; the borer can cause debilitating damage from the tunneling alone and is a potent psychological weapon.
Some will easily recognize parasitic worms as the borer's source of inspiration.