HABIT OF THE WATER-STRIDER GERRIS REMIGES 401 



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against the current. Experiments have been tried with indi- 

 viduals in which one or both eyes were destroyed. When water 

 was rotated in a dish they swam against the current. 



The sense of smell of the water-strider was tested in the fol- 

 lowing way: A small drop of coal oil was placed on the upper 

 edge of the wall of the aquarium upon which the insects were 

 trying to climb. When they had almost reached the oil, which 

 was gradually moving downward, they stopped, moved their 

 antennae, bent backward and plunged into the water. This 

 experiment was tried with coal oil and ammonia water inter- 

 changeably, the insects commonly responding in the same way. 

 A drop of coal oil was placed on the surface of the water in a 

 corner of the aquarium. When the insects, in calmly gliding 

 around occasionally came near the oil, they stopped, moved 

 their antennae, then retreated. When frightened and in rapid 

 motion they sometimes came directly into the field of the oil, 

 when they would swim back excitedly and try to escape by 

 jumping at the walls of the aquarium at the opposite end. 



These insects seem to have a sense of hearing. When, for 

 instance, a door is slammed, or some loud metallic sound is pro- 

 duced, the animals immediately respond by moving backward. 

 When wingless flies are dropped into the water and are buzzing, 

 the water-striders hurriedly move toward them, while a dead 

 fly may float for a considerable length of time without being 

 discovered. This experiment was tried with Gerris remiges 

 whose eyes had been destroyed, with the same result, the blind 

 insects moving from all directions toward the source of sound. 

 However, they do not respond to all sound equally well. A 

 tuning pipe was attached to one end of a wire, the other- end of 

 which was in the aquarium. The tuning pipe was then blown, 

 but it had little or no effect on the water-striders, which con- 

 tinued their movements at random on the surface of the water. 



SUMMARY 



Gerris remiges are very common and are widely distributed. 

 They are found almost everywhere on the surface of the water, 

 beneath the rocks and in crevices. They are swift of motion, 

 moving forward and backward with equal facility. They are 

 very voracious and carniverous, although they never attack 

 animals below the surface of the water, but only those on the 



