After finding a host and shedding its wings for good, a blood-feeding fly appears to sacrifice some of its vision to better support its parasitic lifestyle.
Researchers from Aberystwyth University and the University of Florence have discovered that this major shift in behavior is accompanied by a significant change in the insects’ sensory systems.
Deer Keds Reduce Investment in Vision
After establishing themselves on a host, deer keds appear to redirect resources away from maintaining highly sensitive vision. Scientists believe this may help conserve energy for functions that become more important once the flies stop flying and begin living as parasites.
Dr. Roger Santer from the Department of Life Sciences at Aberystwyth University, who led the study, said:
“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.”
Comparing Flying and Wingless Deer Keds
To investigate how the insects adapt to this transition, the researchers examined deer keds at different stages of their lives. This included winged adults captured while searching for hosts and wingless adults collected from deer after they had adopted their parasitic lifestyle.
The team focused on genes involved in visual sensitivity, known as opsins. By comparing gene activity before and after the flies shed their wings, the scientists were able to see how the insects’ visual systems respond to such a sudden lifestyle change.
Vision Declines After the Flies Find a Host
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 findings suggest that deer keds retain the ability to see after settling on a host, but their visual sensitivity becomes much lower than it was during their host-seeking stage.
Published in the Journal of Experimental Biology, the study offers new insights into how parasites adjust their sensory systems when their lifestyles undergo dramatic changes.
Researchers say a better understanding of how deer keds and other biting flies use their senses could eventually contribute to improved monitoring and control methods.
Reference: “Visual adaptation of a biting fly that permanently foregoes flight” by Roger D. Santer, David C. Wilcockson, Martin T. Swain, Annalisa Andreani, Anita Nencioni and Patrizia Sacchetti, 31 May 2026, Journal of Experimental Biology.
DOI: 10.1242/jeb.251571
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