3. White flowers are often fertilised by moths, and very frequently give out their scent only by night, as in our butterfly-orchis (Habenaria chlorantha); and they sometimes open only at night, as do many of the evening primroses and other flowers. These flowers are often long tubed in accordance with the length of the moths' probosces, as in the genus Pancratium, our butterfly orchis, white jasmine, and a host of others. 4. Bright red flowers are very attractive to butterflies, and are sometimes specially adapted to be fertilised by them, as in many pinks (Dianthus deltoides, D. superbus, D. atrorubens), the corn-cockle (Lychnis Githago), and many others. Blue flowers are especially attractive to bees and other hymenoptera (though they frequent flowers of all colours), no less than sixty-seven species of this order having been observed to visit the common "sheep's-bit" (Jasione montana). Dull yellow or brownish flowers, some of which smell like carrion, are attractive to flies, as the Arum and Aristolochia; while the dull purplish flowers of the Scrophularia are specially attractive to wasps. 5. Some flowers have neither scent nor nectar, and yet attract insects by sham nectaries! In the herb-paris (Paris quadrifolia) the ovary glistens as if moist, and flies alight on it and carry away pollen to another flower; while in grass of parnassus (Parnassia palustris) there are a number of small stalked yellow balls near the base of the flower, which look like drops of honey but are really dry. In this case there is a little nectar lower down, but the special attraction is a sham; and as there are fresh broods of insects every year, it takes time for them to learn by experience, and thus enough are always deceived to effect cross-fertilisation.[147] This is analogous to the case of the young birds, which have to learn by experience the insects that are inedible, as explained at page 253. 6. Many flowers change their colour as soon as fertilised; and this is beneficial, as it enables bees to avoid wasting time in visiting those blossoms which have been already fertilised and their nectar exhausted. The common lungwort (Pulmonaria officinalis), is at first red, but later turns blue; and H. Müller observed bees visiting many red flowers in succession, but neglecting the blue. In South Brazil there is a species of Lantana, whose flowers are yellow the first day, orange the second, and purple the third; and Dr. Fritz Müller observed that many butterflies visited the yellow flowers only, some both the yellow and the orange flowers, but none the purple.