Figure 1.
Mayflies attracted en masse to shiny black cars due to the highly and horizontally polarized light reflected from the car-body.
(A, B) Mass-swarming Ephemerella hendrickson. (C) Egg-laying Ephemera danica. (D) Thousands of mass-swarming female Ephoron virgo mayflies landed on a windscreen, onto which they laid their yellow egg batches. Photos A and B were taken by Dr. Rebecca Allen (Michigan State University, USA), while photos C and D originate from Dr. György Kriska (Eötvös University, Budapest, Hungary).
Figure 2.
Photograph, patterns of the degree of linear polarization d and the angle of polarization α (clockwise from the vertical), and areas detected as water by polarotactic insects (for which the reflected light has the following characteristics: d>15%, 80o<α<100o) of a matt black car measured with imaging polarimetry from five different directions of view in the blue (450 nm) part of the spectrum.
The angle of elevation of the optical axis of the polarimeter was −20o from the horizontal. The number-plate of the car is screened by a white rectangle.
Figure 3.
Degree of linear polarization d of the shiny black (sb), matt black (mb) and matt grey (mg) horizontal test surfaces used in experiments 1 and 2 measured with imaging polarimetry in the red (650 nm), green (550 nm) and blue (450 nm) parts of the spectrum when sun- and skylight (A, Supplementary Fig. S4I) or canopylight originating from trees and bushes (B, Supplementary Fig. S4II) was reflected by the test surfaces.
Columns: averages. Vertical bars: standard deviations. The average is calculated for the whole area of each test surface (corresponding to 2500×4000 = 10 000 000 pixels in the pictures and polarization patterns).
Table 1.
Degree of linear polarization d (average ± standard deviation, averaged to the whole surface area) of the three horizontal test surfaces (shiny black, matt black, matt grey) used in experiments 1 and 2 measured with imaging polarimetry in the red (650 nm), green (550 nm) and blue (450 nm) parts of the spectrum when sun- and skylight (Fig. S4I) or canopylight originating from trees and bushes (Fig. S4II) was reflected by the test surfaces.
Figure 4.
Total numbers of mayflies landed on the shiny black, matt black and matt grey horizontal test surfaces in experiment 1.
The inset is a photograph of a mayfly landed on the shiny black test surface. The number of repetition is 6 (see Materials and methods, and Discussion).
Table 2.
Statistical comparisons (Kruskal Wallis and Mann-Whitney U test) between the numbers of mayflies landed on the shiny black, matt black and matt grey horizontal test surfaces in experiment 1 (Fig. 4, Table S1).
Figure 5.
Total numbers of dolichopodids landed on the shiny black, matt black and matt grey horizontal test surfaces in experiment 1.
The inset is a photograph of a dolichopodid fly landed on the matt black test surface. The number of repetition is 6 (see Materials and methods, and Discussion).
Table 3.
Statistical comparisons (Kruskal Wallis and Mann-Whitney U test) between the numbers of dolichopodids landed on the shiny black, matt black and matt grey horizontal test surfaces in experiment 1 (Fig. 4, Table S1).
Figure 6.
Total numbers of reactions (touching, landing and aerial looping) of tabanids to the shiny black (sb), matt black (mb) and matt grey (mg) horizontal test surfaces in experiment 2.
The inset is a photograph of a tabanid fly landed on the matt grey test surface. The number of repetition is 20 (see Materials and methods, and Discussion).
Table 4.
Statistical comparisons (Kruskal Wallis and Mann-Whitney U test) between the numbers of the three reactions (landing, touching, looping) of tabanids to the shiny black, matt black and matt grey horizontal test surfaces in experiment 2 (Fig. 6, Table S2).