Which of the following flies remains with the animal at all times?

The horse fly is known for its persistent behavior of staying close to the animal it infests. Unlike many other types of flies that may land on livestock for only short periods, horse flies tend to remain nearby while actively pursuing the animal for feeding. This characteristic is tied to their feeding habits; they are aggressive feeders that require a steady host to obtain blood, which they do by biting into the skin of the animal.

In contrast, deer flies and black flies may also feed on animals but typically don’t stay as closely tied to them for extended periods compared to horse flies. Other flies, such as house flies, are more opportunistic and do not specifically target animals as hosts; they can be found in various environments and often move from one location to another.