NATURAL ENEMIES. 



The subject of the practical use of natural enemies of mosquitoes is considered 

 in the section of " Remedies." As virtually the only natural enemies of mos- 

 quitoes which can be used practically are fish, a rather full consideration of fish 

 will be found in that portion of this work, and is omitted in this present treat- 

 ment. 



PLANTS. 



At least two groups of herbaceous plants contain mosquito destroyers. The 

 bladderworts (Lentibulariaceas) of the genus Utricidaria, living in water, have 

 little bladders which trap small aquatic animals. The bladders have each a 

 valve-like door through which the animals enter when looking for food or when 

 trying to escape from their natural enemies. Darwin, in his work on insectiv- 

 orous plants, cites observations made by Mrs. Treat in New Jersey with Utric- 

 ularia clandestina. It was found that larvas, probably those of mosquitoes, 

 when " feeding near the entrance, are pretty certain to run their heads into the 

 net, whence there is no retreat. . . ." Fully nine out of every ten bladders con- 

 tained these larvae or their remains. The species which grow in stagnant waters 

 have the most effective bladders. Mosquito larvae inhabiting stagnant pools in 

 which the Utricularia grows are quite often entrapped in this way. 



Recently J. H. Hart has kept under observation a species of Utriaidaria which 

 occurs in pools at the Pitch Lake in the island of Trinidad. He found dead 

 mosquito larvas in the bladders and also newly caught ones struggling for free- 

 dom which afterwards succumbed. Eysell gives photographic reproductions of 

 Utricularia with mosquito larvae in the bladders. 



Ernst Krause * has called attention to the presence of Utricularia, in Brazil, 

 in the water accumulations between the bases of the leaves of bromeliaceous 

 plants, and as these water accumulations have since been shown to be fertile 

 breeding-places for certain species of mosquitoes, it is very probable that the 

 Utricularia here exercises a certain degree of mosquito control. 



Another Brazilian bladderwort, Oenlisea ornata, is said by Dr. Adolf Eysell 

 to capture mosquito larvae. He compares the tubular leaves of this plant to an 

 eel-trap. 



According to the same author a member of the sundew family (Droseraces), 

 which grows submerged, captures mosquito larvae. This is the Aldrovanda 

 vesiculosa of southern Europe and the adjacent warm countries, the leaves of 

 which have a structure and function similar to that of the well-known Venus's 

 fly-trap (Dionea viuscipula) , its leaves closing quickly upon any insect that 

 touches them. 



• Die Schutzmittel der BlUthen gegen unbenifene Gaste (Kosmos, 1887, vol. 1, p. 80). 

 156 



