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Why do blowflies resume feeding sooner when they use more energy?

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Two wild horses graze on tall grass in the open prairie of Theodore Roosevelt National Park, with rolling badlands visible in the background. — Feeding behaviour Wild horses graze in the Badlands of North Dakota.

Blowflies, such as the blowfly Phormia regina, regulate their food intake based on the nutrient concentration of their body fluids. This concentration is determined by the balance between the absorption of nutrients from the gut and the uptake of those nutrients by metabolizing tissues.1

When a blowfly exerts more energy, its metabolizing tissues consume nutrients from the body fluids at a faster rate. This increased consumption lowers the nutrient concentration in the body fluids, which in turn accelerates the rate at which the fly's crop is emptied. Because the threshold for the fly's sucking response remains high until the crop is completely voided, the faster emptying of the crop allows the fly to resume feeding sooner. This physiological mechanism ensures that the fly's food intake remains balanced with its caloric expenditure through the appropriate spacing of meals.1