Biting flies and warm “targets”

This may give some horse owners and explanation for what they are seeing and some ideas of how to mitigate the problem of biting flies in the pasture.
DrO

PLoS One. 2020 May 13;15(5):e0233038.
Why do biting horseflies prefer warmer hosts? tabanids can escape easier from warmer targets.
Horváth G1, Pereszlényi Á1,2, Egri Á3,4, Tóth T1, Jánosi IM5.

Author information:
1. Department of Biological Physics, ELTE Eötvös Loránd University, Budapest, Hungary.
2. Department of Zoology, Hungarian Natural History Museum, Budapest, Hungary.
3. MTA Centre for Ecological Research, Danube Research Institute, Budapest, Hungary.
4. Evolutionary Systems Research Group, MTA Centre for Ecological Research, Tihany, Hungary.
5. Department of Physics of Complex Systems, ELTE Eötvös Loránd University, Budapest, Hungary.
Abstract

Blood-sucking horseflies (tabanids) prefer warmer (sunlit, darker) host animals and generally attack them in sunshine, the reason for which was unknown until now. Recently, it was hypothesized that blood-seeking female tabanids prefer elevated temperatures, because their wing muscles are quicker and their nervous system functions better at a warmer body temperature brought about by warmer microclimate, and thus they can more successfully avoid the host’s parasite-repelling reactions by prompt takeoffs. To test this hypothesis, we studied in field experiments the success rate of escape reactions of tabanids that landed on black targets as a function of the target temperature, and measured the surface temperature of differently coloured horses with thermography. We found that the escape success of tabanids decreased with decreasing target temperature, that is escape success is driven by temperature. Our results explain the behaviour of biting horseflies that they prefer warmer hosts against colder ones. Since in sunshine the darker the host the warmer its body surface, our results also explain why horseflies prefer sunlit dark (brown, black) hosts against bright (beige, white) ones, and why these parasites attack their hosts usually in sunshine, rather than under shaded conditions.