442 SYMBIOSIS BETWEEN AN ASCLEPIAS AND A BUTTERFLY. 



It is also remarkable that Danais Eiuipus has followed the 

 wanderings of the Asclepias, which has spread from America over 

 the warmer parts of the globe. Whether this following is complete, 

 or whether the butterfly has not yet penetrated to some places, and 

 other insects suffice for fertilization, I am unable to determine from 

 the literature at my disposal. As shown above, fertilization by 

 means of other insects is not an impossibility, but it is not so 

 constant ; therefore Danais Euripus plays at any rate the most 

 important part in the proceeding, and certainly is always to be 

 found wherever Asclepias carassavica grows in America. In most 

 flowers which are specialized for certain visitors, viz. humming- 

 birds, Sphingidae, and humble-bees, chance fertilization occurs 

 through quite different agents. In South Brazil this same butterfly 

 lives also on Asclepias campestris Decne. (regarded by Grisebach 

 as A. curassavica L.), and another variety is also said to be found 

 there. 



The Asclepiad gives therefore board and lodging to the butterfly 

 in its caterpillar state, and when the insect is developed, the plant, 

 while refreshing it with sweet nectar, protects it also from enemies ; 

 for the wings of the butterfly, when spread out, resemble in colour-'- 

 the umbel in bloom, and when folded those in bud. 



In return for this service Danais fertilizes the Asclepias, and in 

 this way multiplies and supports it. It may be mentioned that the 

 caterpillars are much scattered, and seldom do much damage to the 

 plants, which are avoided as poisonous by grazing animals. Such 

 a mutual and constant association of insect and plant is certainly 

 worthy of notice, and may be best compared with that of ants and 

 Cecropia. I will add an observation which may throw light on this 

 latter connection. 



In the swamp near Moua, especially at the edge of the Eestinga, 

 where Sphagnum is often found, there grows plentifully a dwarf 

 Cecropia rough with hairs, which often attains a height of one or 

 two metres ; on this I have always found a great number of ants. 

 To my surprise I found one day in the cold season all the Cecropics 

 free from ants, a circumstance which I examined into more closely, 

 and to this end cut open the stem. There I found in each of the 

 upper chambers (internodes) a large wingless female. From this 

 it would appear that all the working ants die off at certain times 

 (whether the species be peculiar to the swamp species of Cecropia, or 

 not, remains an open question), and the females then found new 

 colonies, resembling in this way the wasps in Germany. 



In connection with this may be mentioned the case brought 

 forward by Alfred Moller (Bot. Mitth. a. d. Tropen, Heft 6, s. 82) 



* I am inclined to think that the gay colour of the butterfly has arisen 

 partly from imitation of the flowers which it visits, in order to escape thereby 

 from its pursuers. The likeness between night-moths and rocks, bark and 

 lichen, as well as the resemblance of stationary day-moths and caterpillars to 

 leaves (so-called mimicry) is well known. In the same way the bright colour of 

 many butterflies has arisen in imitation of flowers, although, on the other hand, 

 much fine colouration cannot be explained that way, but must be regarded as a 

 kind of luxury. 



