What effect does the bite of Horse flies and Deer flies have?

The bite of horse flies and deer flies is particularly notable for promoting a considerable flow of blood. These flies are known for their biting habits; their mouthparts are adapted to cut through the skin of their host, which results in not just skin irritation but also an actual wound that can lead to blood loss. The mechanism of their bite is such that they feed on blood, and during this process, they trigger a response that results in increased blood circulation to the area.

Furthermore, this increased blood flow can be attributed to the inflammatory response initiated by the body to deal with the injury caused by the bite. This reaction is the body’s way of delivering immune cells and other healing factors to the site of the bite. While the irritation and potential for infection can also occur due to the bites, the immediate and characteristic effect observed with horse and deer fly bites is the substantial blood flow induced by their feeding behavior.

The other choices relate to secondary outcomes or effects that follow the initial and significant response of blood flow during the biting process.