The case of the missing unborn flies may have a solution: prenatal cannibalism.
Females of the small fly species Emblemasoma auditrix deposit their larvae on cicadas, insects on which the youngsters feed for about 5 days. Those larvae hatch from eggs while still inside their E. auditrix mother. While Mom carries a brood of some 38 wriggling larvae equipped with sharp mouthparts, she deposits only one larva on each cicada that she finds.
Since the mother fly's hunt for cicadas lasts several weeks, some of the larvae face a long wait for food, says Reinhard Lakes-Harlan of the Justus-Liebig-University Giessen in Germany. To study what happens during that wait, he and his colleague from Germany, Thomas de Vries caught pregnant female flies in Michigan.