441 



SYMBIOSIS BETWEEN AN ASCLEPIAS and a BUTTERFLY.* 



By E. Ule. 



In whatever fields and pastures in Brazil Asclepias curassavica L. 

 is found, there is to be seen either a large red-brown spotted butterfly 

 flying about near it or at least some of the caterpillars on the plant. 

 Inversely, to find the butterfly argues the proximity of the plant. 

 This butterfly is Danais Euripus, a large species (surpassing in 

 width from wing to wing the German species of Vanessa), which 

 is developed almost the whole year round and flies away with 

 difficulty. 



It is well known that many butterflies are confined to special 

 plants for their food, and are always to be fovmd at certain times in 

 their neighbourhood; but such a marked and constant connection 

 as this is not known to me at all in the case of any other large 

 butterfly. Feeling sure that this occurrence must have a special 

 cause, I made observations, and remarked that Danais Euripus is 

 the principal fertilizing agent of Asclepias curassavica L.f Some 

 other butterfly may now and again fly to the blossoms of this 

 Asclepiad, or wasps may settle upon it, but none of these insects 

 are such constant and specialized visitors as D. Euripus. When it 

 settles on an umbel to sip the nectar, it generally runs its legs into 

 the flower by its somewhat clumsy movements, and drags out the 

 pollinia. All the specimens which I caught had their legs more or 

 less covered with sticky attachments and lumps of pollen. Some- 

 times I recognized pollinia which had been pushed in, and in one 

 flower there were as many as three pollinia with their attachments 

 pressed into the slit, while above, in the anther-pocket, there still 

 remained the original polliuium. 



The butterfly very seldom pays even a single visit to the flowers 

 of another plant ; as a rule, it is only to be seen on Asclepias 

 curassavica L., scorning all other nectariferous flowers in the 

 neighbourhood. In one field where this Asclepiad was plentiful 

 there were other butterflies, but these visited more the flowers of a 

 ilijptis and Crotalaria. Whenever they did go to the Asclepias 

 flowers, they became covered with pollinia, as did also a large wasp 

 (Polistes canadensis L.) which was common there. More delicate 

 and less clumsy insects did not become thus covered. 



* [Translated from Berichte der Deutschen Bot. Gesellschaft xv. 385-7 

 (7 Sept. 1897). Dr. Buchanan White's paper, referred to in the first footnote, 

 was pubhshed in this Journal for 1873, pp. 11-13. — Ed. Journ. Bot.] 



t According to communications of B. White (Bot. Jahresb. 1873, p. 378), 

 species of the genus Dianf/w'c/rt of Noctuidffi fertilize those species of Lychnis 

 and Silenc in whose capsules live the caterpillars of the said butterflies. The 

 same investigator takes for granted a mutual dependence in the geographical 

 distribution of Sphinx ConvolvuU and CunvolcnUis scpiuin. In the latter case, 

 however, it is to be noticed that the caterpillar of Sphinx ConvolvuU occurs 

 principally on Convolvulus arvensia. On the other hand, the case of the so-called 

 Yucca moth {Pronuha Yuccasclla) and the smaller Lepidoptera shows a mutual 

 dependence not less genuine than in our Asclepias butterfly. 



