22 CAMFORMA FISH AND GAME. 



FACTORS RENDERING THE STICKLEBACK AN EFFICIENT MOSQUITO 



DESTROYER. 



1. The stickleback tises mosquitoes as food. This point is to be 

 proved first of all. The evidence is convincing. The stickleback has 

 been seen snapping up adult mosquitoes thrown into the water. Mos- 

 quitoes are unable to breed in waters inhabited by sticklebacks. This 

 conclusion, previously arrived at in regard to the stickleback and the 

 salt-marsh mosquito of San Francisco Bay, has been rigidly tested out 

 in many of the streams from San Francisco south to the Mexican 

 border. Only a few examples from the observations can be made here. 



In San Francisquito Creek, near Palo Alto, pools were repeatedly 

 found near one another and apparently similar except in this respect: 

 in the one pool sticklebacks were plentiful, but no mosquito wrigglers 

 could be detected, Mhile in the other pool sticklebacks were absent, 

 while mosquitoes were breeding in abundance. 



The swamps, pools and streams of the coast region of San Luis 

 Obispo and Santa Barbara counties appear as ideal breeding Avaters 

 for mosquitoes, yet the people there enjoy unusual freedom from these 

 pests and dangers. A study of the region makes it almost certain that 

 these people have the stickleback to thank for the service thus rendered. 

 But, even in these regions mosquitoes breed in abundance in the moun- 

 tain canyons into which the sticklebacks can not ])enetrate because of 

 the steep descent of the bouldery stream beds. The mosquitoes are 

 forced back, however, into the mountains where there are fewer people 

 for them to torment. 



In Mission Valley in San Diego sticklebacks are, for some unknown 

 reason, entirely absent, but mosquitoes and gnats are very troublesome 

 during the summer months. From the valley the mosquitoes are blown 

 up the canyons to the city on the mesa above. During the summer 

 the surface waters of the San Diego River, M^hich flows through Mis- 

 sion Valley, are reduced to a series of pools. In these pools three 

 introduced fishes, the golden bream (Notemigomus crysoleucas) , the 

 bullhead (Ayneiurus nehulosus), and the green sunfish (Lepomis cya- 

 nellus) are generally abundant. It seems that the stickleback is more 

 efficient in the control of mosquitoes than are these three other fishes 

 together. 



During an entire summer's study of this problem, I never noted a 

 (considerable number of either mosquito wrigglers or sticklebacks in 

 the same pool together. Wherever the stickleback can penetrate, and 

 they go as far as they can, the mosquitoes are effectively destroyed. 



2. Abundance of other food will not deter the stickleback from feed- 

 ing on the mosquito wrigglers. This conclusion is evident from field 

 observations, and is confirmed by the size and structure of the fish : its 

 mouth, small even for such tiny fi.shes, will not permit it to feed on 

 large insect larvte such as those of dragon flies, which, by the way, 

 upon emerging as the adult insect, feed upon the mosquitoes in the air. 



3. The stickleback feeds at all levels of the water, from bottom to 

 surface. Because of this fact, mosquito wrigglers of different habits are 

 all picked up. Statements published by Seal, and by Lutz and Cham- 

 ber for the stickleback of the East Coast, make it appear a bottom 

 feeder. At least, such a conclusion does not apply to the stickleback of 



