6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



reduced or suppressed, and the proboscis limits the diet of the moth 

 or butterfly to readily accessible liquids, which are mostly the nectar 

 of flowers. This fact determines the essential structure not only of 

 the adult lepidopteron, but that of the caterpillar as well. The intake 

 of liquid food necessitates the possession of an efficient sucking 

 apparatus connected with the alimentary canal, while the alimentary 

 canal itself can be much simplified by comparison with that of an 

 insect that feeds on solid food. 



Butterflies, it is true, do not feed entirely on nectar ; some are able 

 to rasp fruit for the juice, others may suck up sap exuding from trees, 

 or imbibe honeydew from aphids, and they have been seen apparently 

 feeding on carrion and excreta. They all drink water. So far as 

 known, the only digestive enzyme of adult Lepidoptera is invertase. 

 Swingle (1928) reports the presence of only this enzyme in the 

 oriental fruit moth, and in elaborate studies on digestion in various 

 adult Lepidoptera Stober (1927) found no other digestive enzyme 

 than invertase. It appears, therefore, that adult Lepidoptera can digest 

 only cane sugar. When small quantities of starch, fat, or protein 

 (blood) are mixed with their food, these substances, Stober says, 

 remain unchanged in the stomach. Glucose, of course, can be absorbed 

 as obtained in nature. Species with reduced mouth parts that do not 

 feed as adults were found to have no digestive enzymes. It is not 

 known what butterflies seen apparently feeding on carrion or excre- 

 ment may get from such sources. Possibly the juices contain products 

 of bacterial decomposition that can be directly absorbed as predigested 

 food. 



Inasmuch as a few modern moths have vestigial mandibles, there 

 can be little question that present-day Lepidoptera are descended from 

 adult progenitors that fed on solid food. Their adaptation for a liquid 

 diet, therefore, must have been made when the early ancestors of the 

 moths and butterflies renounced solid food for liquids. The proboscis 

 is formed of the maxillary galeae, and is probably not a functional 

 organ of great antiquity, since early stages of its evolution are still 

 preserved in two primitive families, the Eriocraniidae and the Mnes- 

 archaeidae. Except for one doubtful form, fossil Lepidoptera are not 

 known much before the Eocene. 



At the time when the Lepidoptera first appeared in evolution, the 

 mutual relationship between flowers and insects had already been 

 established. Flowers had bright colors and probably attractive odors, 

 and their pollen formed a nutritious food for insects. Thus the plants 

 fed the insects, and the insects pollinated the plants. 



The Micropterygidae have long been regarded as a primitive 



