44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



to understand why so many of them are endowed with such brilliant 

 coloration and color patterns — surely not to appeal only to our esthetic 

 sense and make attractive displays in the specimen cases of entomolo- 

 gists. It would seem, then, that we need a theory to explain their 

 colors on a scientific basis of usefulness to the insects themselves. The 

 same might apply to the colors and designs of seashells (or perhaps 

 also to the beauty of a landscape). 



Most butterflies live lives of unfettered freedom. They toil not, 

 neither do they spin, nor make provision for the future, and yet no 

 other insect is arrayed like some of them. Flitting from flower to 

 flower, sipping nectar, courtship and marriage — this is the life of a 

 butterfly. Only when the time comes for egg laying does the female 

 moth or butterfly meet her one responsibility. Since many caterpillars 

 are very particular about what plants or other material they feed on, 

 the adult female must deposit her eggs where the young caterpillars 

 on hatching will find their proper food. It seems as if the female 

 retains a memory of her own caterpillar days, and the same maternal 

 instinct is shared by various other insects. This "instinct," however, 

 has been shown by Thorpe and Jones (1937) and by Thorpe (1938, 

 1939) to be due, in some insects at least, to the olfactory conditioning 

 of the larva to its food, which is carried over to the adult female and 

 induces her return to a source of the same odor. This is not exactly 

 memory in the human sense, and it is probably more reliable, but it 

 does not explain the possession by the female of a return instinct. 

 A remarkable example of this instinct is shown by the monarch 

 butterfly, the larvae of which feed on the milkweed. In the fall many 

 adults in northern regions migrate in flocks to the south, where they 

 spend the winter; in the spring the females return north and find 

 milkweeds on which to deposit their eggs. 



The conditioning factor of the return instinct is not always food ; 

 the female dragonfly or the female mosquito must deposit her eggs 

 in an aquatic environment suitable to the larvae. The same is true of 

 the moth Nymphula, the larvae of which are aquatic. The females of 

 N. maculalis described by Welch (1916) lay their eggs on the under- 

 sur faces of leaves of the yellow waterlily, using wherever available 

 oviposition holes cut in the leaves by the beetle Donacxa. The moth 

 inserts her abdomen through one of these holes and attaches her eggs 

 to the underside of the leaf in concentric circles around the beetle eggs. 

 The moths are said to remain in the neighborhood of the water, but 

 certainly no larval conditioning could account for their special ovi- 

 positing instinct. The larvae live submerged on the undersides of 



