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The eggs hatch inside the female abdomen (one at the time ;)) and the larva is fed it the female abdomen. As soon as the larva is full-grown it will be deposited in a proper place (as 'pre-pupa') and pupate immediately. Then the next eggs will hatch and the cycle starts again.
It may seem laborious and little productive, but acually larval survival may be higher in Hippoboscidae than in many 'regular' species, where there can occur high mortality aong eggs and larvae because of predators, parsites and parasitoids, let alone infections of fungi. Remember, you only need two reproducing descendants (preferably a male and a female ;)) to keep the species surviving.