Asphalt surfaces as ecological traps for water-seeking polarotactic insects: How can the polarized light pollution of asphalt surfaces be reduced?

Péter Malik, Ramón Hegedüs, György Kriska, Susanne Åkesson, Bruce Robertson, Gábor Horváth

Research output: Chapter in Book/Report/Conference proceedingChapter

1 Citation (Scopus)


The surface of dry or wet asphalt roads reflects partially linearly polarized light, the degree of linear polarization p of which depends on the darkness and roughness of asphalt: the darker and/or the smoother the asphalt, the higher the p of light reflected from it. If the asphalt is sunlit and the direction of view is parallel to the solar-antisolar meridian, then the direction of polarization of asphalt-reflected light is horizontal. In this case the asphalt surface can attract water-seeking aquatic insects, because they detect water by means of the horizontal polarization of light reflected from the water surface. This phenomenon is called positive polarotaxis. Polarotactic insects mistaking asphalt surfaces for water bodies lay their eggs upon dry asphalt after copulation, where the eggs perish due to dehydration. The polarization signal of the asphalt surface can be so strong that insects can actively prefer asphalt over water as an oviposition site. This phenomenon is well studied for mass-swarming mayflies, but other polarotactic insects, such as dragonflies, caddisflies, stoneflies, water beetles and aquatic bugs can also be deceived by and attracted to asphalt roads near natural water bodies. We refer to the negative survival and reproductive consequences of artificial sources of polarized light on polarotactic organisms as polarized light pollution. Highly and horizontally polarizing asphalt roads are sources of polarized light pollution that can create ecological traps for polarotactic insects when they become more attractive than natural habitats. Trapped populations are predicted to have a high probability of extinction, and so paved surfaces may threaten populations of endangered aquatic insect species. An ecological trap for water insects can further trigger a secondary ecological trap for other vertebrate species that prey upon the water insects attracted to the asphalt: these insects and the carcasses of vehicle-killed polarotactic insects can attract different insectivorous vertebrates, especially birds, which can also be run down by the cars. In this work we study the polarizing characteristics of asphalt surfaces as functions of the surface features (roughness, darkness, painted with white striates or not), the illumination conditions (sunny or shady), and the direction of view relative to the solar meridian. On the basis of these data we suggest some possible strategies to mitigate the severity of polarized light pollution produced by asphalt. In areas with gravel roads, for example, change of the gravel to the more insect-attracting asphalt should, if possible, be avoided. We show how the degree of polarization p of asphalt-reflected light can be reduced under the threshold of polarization sensitivity of aquatic insects: the roughness, brightness and white-striateness of the asphalt surface should be increased in order to reduce p, and thus the attractiveness to polarotactic insects. We propose the use of these remedies on asphalt roads running near emergence sites of endangered aquatic insects, especially in the vicinity of wetlands, rivers and lakes. Conservation biologists may effect substantial benefits for aquatic insects and their ecosystems by working with asphalt road planners to reduce the attractiveness of asphalt surfaces to polarotactic species.

Original languageEnglish
Title of host publicationAsphaltenes
Subtitle of host publicationCharacterization, Properties and Applications
PublisherNova Science Publishers, Inc.
Number of pages39
ISBN (Print)9781607414537
Publication statusPublished - Dec 1 2010



  • Aquatic insects
  • Asphalt surface
  • Ecological trap
  • Imaging polarimetry
  • Polarization vision
  • Polarized light pollution
  • Polarotaxis
  • Reflection polarization
  • Visual ecology

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Malik, P., Hegedüs, R., Kriska, G., Åkesson, S., Robertson, B., & Horváth, G. (2010). Asphalt surfaces as ecological traps for water-seeking polarotactic insects: How can the polarized light pollution of asphalt surfaces be reduced? In Asphaltenes: Characterization, Properties and Applications (pp. 81-119). Nova Science Publishers, Inc..