What do both male and female stable flies primarily feed on?

Stable flies, both males and females, primarily feed on blood, which is essential for their reproductive processes. The females require blood meals specifically to develop their eggs, as the proteins and nutrients in the blood support egg maturation. Males, while they also partake in blood feeding, tend to feed more on sugars from nectar as well. However, when it comes to the primary nutrient source for reproduction, blood is the essential element for both sexes.

The other options do not represent the fundamental dietary habits of stable flies. While stable flies may be seen around plant nectar, this is not their primary nutritional source related to reproduction. Carnivorous insects and fruits do not constitute a significant part of their diet, making blood the only correct choice when it comes to their feeding habits.