This blood-feeding fly sacrifices its sight after finding a host

Known as deer keds, these biting flies are found throughout Europe, Asia, Africa, and the Americas. As adults, they use both flight and vision to search for a suitable host, most often deer, though they sometimes target humans and other mammals.

Once a deer ked lands on a host, its lifestyle changes dramatically. The insect permanently sheds its wings and spends the remainder of its life moving through fur and feeding on blood.

Scientists from Aberystwyth University and the University of Florence have discovered that this major behavioral shift is accompanied by changes in the fly's sensory system.

Their findings suggest that after settling on a host, deer keds reduce investment in vision and redirect energy toward functions that are more important for life as a permanent parasite.

From Flying Hunter to Permanent Parasite

Dr. Roger Santer from the Department of Life Sciences at Aberystwyth University, who led the study, explained:

"Vision plays a vital role in animal behavior, but it is also energetically expensive. Evolution favors sensory systems that are efficiently matched to an animal's way of life. Some blood-feeding flies rely heavily on vision, while others live permanently on hosts and have little need for it. Deer keds are especially interesting because they switch between these two lifestyles."

To investigate how the insects adapt to this dramatic transition, researchers studied deer keds at different points in their life cycle. They examined winged adults that were actively searching for hosts and compared them with wingless adults collected from deer after they had adopted their parasitic lifestyle.

Visual Genes Become Less Active

The team focused on genes associated with visual sensitivity, known as opsins. By comparing gene activity before and after the flies shed their wings, the researchers were able to see how the insects' visual systems respond to their sudden change in lifestyle.

Dr. Santer said:

"We found that a flying deer ked's visual system is much like that of a tsetse fly, which famously hunt out mammal hosts in Africa. However, after a deer ked loses its wings and becomes an ectoparasite, activity of its opsin genes reduces to around half the previous level. This suggests that the flies do not lose vision entirely, but that their visual sensitivity is reduced. We think the fly might be sacrificing sight to conserve energy for functions such as digestion and reproduction."

The results indicate that deer keds do not become blind after finding a host. Instead, they appear to scale back their visual capabilities once they no longer need to search for animals from the air.

New Insights Into Parasite Adaptation

Published in the Journal of Experimental Biology, the study provides fresh insight into how parasites adjust their sensory systems when their lifestyles change dramatically.

Researchers say a better understanding of how deer keds and other biting flies use their senses could eventually contribute to improved monitoring and control strategies.