Fatigued is good (IIRC, that stacks with itself to become exhausted, etc). Maybe after 2 consecutive days of insufficient feeding, it starts taking Con damage? Should we add something like this to a normal peltast? I think we just left the feeding as flavor text.
Blood Feeding (Ex): A greater peltast must feed on blood each day; it may do so by biting a living creature, in which case it must do 3 hp of damage per day to sustain itself. A greater peltast may also gain sustenance from the blood of dead creatures, and it can lap up the equivalent of 1 hp from each creature of at least 1HD. If a greater peltast is able to feed on more than the equivalent of 3hp per day, it gains the remainder as temporary hp (max 10), which last for 24 hours.
If a greater peltast does not feed sufficiently for a day, it becomes fatigued. Starting on the 3rd consecutive day that it does not feed sufficiently, a greater peltast takes 1 point of Con damage per day, which cannot heal naturally until the greater peltast has fed sufficiently at least one day.