![]() Our field experiment was performed in the Hungarian Hortobágy National Park, on the shore of Hagymás-basin marsh (47☃3′29″ N, 20★5′29″ E 10×10 km Universal Transverse Mercator (UTM) grid code: DT 96) characterized by patchy vegetation with a rich and diverse aquatic insect community. Considering water insect protection in wetland habitats, we discuss the question: what is the environmentally friendly colour of cars? We show that the visual deception of aquatic insects by red cars can be explained solely by the reflection–polarizational characteristics of car-bodies. On the basis of these field experiments and polarization measurements, we provide here a novel solution to the previously perplexing question of why red cars attract aquatic insects. Since aquatic insects detect water by means of the high and horizontal polarization of light reflected from the water surface ( Schwind 1991, 1995), we measured the reflection–polarizational characteristics of red, yellow, white and black cars in the red, green and blue parts of the spectrum. ![]() To reveal the visual ecological reasons for this phenomenon, we monitored the numbers of aquatic beetles (Coleoptera) and bugs (Heteroptera) attracted to horizontal shiny red, yellow, white and black plastic sheets. 2001 Günther 2003 Torralba & Ocharan 2003 Wildermuth & Horváth 2005) have been observed to swarm above cars, in particular the landing of water insects on red cars has drawn the attention of the community of researchers studying water insect migration ( Jäch 1997 Nilsson 1997 Vondel 1998). Although different insect species associated with water, especially dragonfly species ( Wyniger 1955 Svihla 1961 Watson 1992 Wildermuth 1998 Stevani et al. Coleoptera and Heteroptera) often swarm in large numbers, mate above and land on the roofs, bonnets and boots of black or red cars and Ephemeroptera and Odonata females often lay their eggs en masse on these car surfaces ( figure 1). 2001), which was explained by the shiny appearance or the red colour of the car-body ( Jäch 1997 Nilsson 1997), or was considered enigmatic ( Vondel 1998). The visual deception of aquatic insects by cars can be explained solely by the reflection–polarizational characteristics of the car paintwork.Īquatic insects are frequently observed to land on red cars ( Jäch 1997 Nilsson 1997 Kriska et al. ![]() Consequently, yellow and white cars are unattractive to polarotactic water insects. The p of light reflected from the horizontal surfaces of yellow and white cars is low and its direction of polarization is usually not horizontal. Thus, the horizontal surfaces of red and black cars are highly attractive to red-blind polarotactic water insects. In the blue and green, the degree of linear polarization p of light reflected from red and black cars is high and the direction of polarization of light reflected from red and black car roofs, bonnets and boots is nearly horizontal. The reflection–polarization patterns of black, white, red and yellow cars were measured in the red, green and blue parts of the spectrum. Monitoring the numbers of aquatic beetles and bugs attracted to shiny black, white, red and yellow horizontal plastic sheets, we found that red and black reflectors are equally highly attractive to water insects, while yellow and white reflectors are unattractive. We reveal here the visual ecological reasons for the phenomenon that aquatic insects often land on red, black and dark-coloured cars.
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