THE VISION OF ARTHROPODS 



585 



tracheal tapetiim fluoresces in ultra-violet light and it would seem 

 probable that the retinal cells are sensitive to rays of this type (Lutz, 

 1924-33 ; Bertholf, 1930-32 ; Lutz and Grisewood, 1934 ; Carter, 

 1948). Photo -negative insects such as the ant thus take shelter from 

 ultra-violet light unseen by the human eye (Lubbock, 1885 ; Forel, 

 1886) and light-seeking insects such as moths and bees are attracted 

 by it (Fig. 732) (Lutz, 1924-33 ; Lutz and Grisewood, 1934). On 

 the other hand, although some species ^ undoubtedly respond to red 

 (up to 690 m/x), most are not attracted by this colovir because of the 

 high threshold but treat red as black. ^ 



In optomotor experiments when dark and light grey stripes are 



57& - 492 436 405 



365 



Fig. 732. — The Spectral Sensitivity of the Honey-Bee. 



Indicating the attraction of the ultra-violet part of the siDectrum. The numbei-s 

 indicate \va\-e-lengths in m/x (Tinbergen, after Klihn). 



Ant 



Moth 



used, the discrimination of luminosity-differences is found to be generally 

 low — about 20 times lower in the bee than in man. and in some other 

 insects poorer still (Wolf, 1933 ; Hecht and Wald, 1934 ; v. Budden- 

 brock, 1935 ; Hundertmark, 1937-38). When coloured light is used 

 as a stimulus it is found that the most effective parts of the spectrum 

 are generally in the yellow-green and ultra-violet, particularly the 

 latter (Fig. 733).'^ The spectral location of the first region corresponds 

 closely to the peak of the luminosity-curve in man, the variation 

 in some insects resembling the human dark-adapted state {Apis) and 



1 Such as butterflies (Pieris, Vanessa — Use, 1928), fire-flies {Pholinus — Buck, 1937) 

 and locust hoiDpers (Locusta — Chapman, 1954). 



2 The honey-bee, Ajiis — v. Frisch (1914), Kiihn (1927) ; the wasj}, Vespa — 

 Schremmer (194"l). 



^ 553 m^ in the yellow-green and 365 ni/tx in the ultra-violet for the bee, Apis, 

 (Bertholf, 1931-32 ; Sander, 1933 ; Weiss et al., 1941-43 ; and others). 540 m/x for 

 the equal energy spectrum in Drosophila (Medioni, 1956). The same applies roughly 

 to Crustaceans (p. 578). 



