Horseflies are often confused with deerflies because they look almost the same and go through their larval stage in much the same kind of environment. However, besides having unique features such as darker wings, horseflies also feed off other mammals besides deer, including humans. The female horsefly is the one that sucks blood from mammals, as male horseflies do not have a large protrusion on the mouth with the same razor-sharp teeth females use to tear into the skin of victims. A female horsefly must have at least one blood meal before she is able to reproduce, and the larval stage can take up to three years.
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Female horseflies lay from 25 to 1,000 eggs. Such a large number may require a lot of room, but the horsefly solves this space issue by laying her eggs in tiers. Horsefly eggs are a dark color and have a spindle shape. The eggs are laid on plants overhanging water, and they hatch in five to 12 days.
The horsefly larval stage takes place in the mud or similar wetland, just as the deerfly's does. The larval stage can last from one to three years. The larvae drop from the eggs into the mud or water and burrow down into the soil. The larvae may also drop into the water then be carried to dry land. The horsefly larva feeds on organic debris, insects and earthworms, as well as other horsefly larva. The larvae mature in the spring and enter the pupal stage.
The pupal stage for a growing horsefly usually takes place on dry soil. The pupal stage is also called the cocoon stage. Depending on the environment and the species, this stage can last from six to 12 days.
The adult horsefly will emerge from the pupae once the pupal stage is complete. This stage usually occurs during the late summer. Adult horseflies are strong fliers and will immediately seek out food as well as a mate. While females will search for a blood meal, the males will feed off nectar and plant juices.