Big baby, little mother: tsetse flies are exceptions to the juvenile small size principle

While across the animal kingdom offspring are born smaller than their parents, notable exceptions exist. Several dipteran species belonging to the Hippoboscoidea superfamily can produce offspring larger than themselves. In this essay, we focus on the blood-feeding tsetse flies. We suggest that the extreme reproductive strategy of this fly is enabled by feeding solely on highly nutritious blood, and producing larval offspring that are soft and malleable.
This immense maternal investment may have evolved to avoid competition with other biting flies. Tsetse flies also transmit blood-borne parasites that cause the fatal diseases called African trypanosomiases. We discuss how tsetse life history and reproductive strategy profoundly influence the type of vector control interventions used to reduce fly populations. In closing, we argue that the unusual life history of tsetse flies warrants their preservation in areas where human and animal health is not threatened.