Liability to the attacks of parasites is also connected with colour. It appears that white chickens are certainly more subject than dark-coloured chickens to the _gapes_, which is caused by a parasitic worm in the trachea.[544] On the other hand, experience has shown that in France the caterpillars which produce white cocoons resist the deadly fungus better than those producing yellow cocoons.[545] Analogous facts have been observed with plants: a new and beautiful white onion, imported from France, though planted close to other kinds, was alone attacked by a parasitic fungus.[546] White verbenas are especially liable to mildew.[547] Near Malaga, during an early period of the vine-disease, the green sorts suffered most; "and red and black grapes, even when interwoven with the sick plants, suffered not at all." In France whole groups of varieties were comparatively free, and others, such as the Chasselas, did not afford a single fortunate exception; but I do not know whether any correlation between colour and liability to disease was here observed.[548] In a former chapter it was shown how curiously liable one variety of the strawberry is to mildew. {229} It is certain that insects regulate in many cases the range and even the existence of the higher animals, whilst living under their natural conditions. Under domestication light-coloured animals suffer most: in Thuringia[549] the inhabitants do not like grey, white, or pale cattle, because they are much more troubled by various kinds of flies than the brown, red, or black cattle. An Albino negro, it has been remarked,[550] was peculiarly sensitive to the bites of insects. In the West Indies[551] it is said that "the only horned cattle fit for work are those which have a good deal of black in them. The white are terribly tormented by the insects; and they are weak and sluggish in proportion to the white." In Devonshire there is a prejudice against white pigs, because it is believed that the sun blisters them when turned out;[552] and I knew a man who would not keep white pigs in Kent, for the same reason. The scorching of flowers by the sun seems likewise to depend much on colour; thus, dark pelargoniums suffer most; and from various accounts it is clear that the cloth-of-gold variety will not withstand a degree of exposure to sunshine which other varieties enjoy. Another amateur asserts that not only all dark-coloured verbenas, but likewise scarlets, suffer from the sun; "the paler kinds stand better, and pale blue is perhaps the best of all." So again with the heartsease (_Viola tricolor_); hot weather suits the blotched sorts, whilst it destroys the beautiful markings of some other kinds.[553] During one extremely cold season in Holland all red-flowered hyacinths were observed to be very inferior in quality. It is believed by many agriculturists that red wheat is hardier in northern climates than white wheat.[554]