June, 1911.] Severin-Severin : Habits of Belostoma and Nepa. 101 



an aquarium in which the water was but an inch in depth, and within 

 a few hours thirty-two of the thirty-five specimens that the aquarium 

 contained were found beneath the corks. Again, it was not unusual 

 to find two or more Belostomas or sometimes large clusters clinging 

 together at the surface or bottom of the water, a characteristic which 

 is also noticed with Lethocerus (=■ Belostoma Aucct.) amcricanimi, 

 Bcnacus griseus, Nepa apiculafa, Ranatra amcricana and Ranatra 

 kirkaldyi. This habit is probably a manifestation of their thigmo- 

 tactic response. 



Food Reactions. — Belostoma is carnivorous. While resting at the 

 surface-film of the water, it often seizes its prey with the front pair 

 of raptorial legs. When in the resting position, the body extends 

 obliquely down in the water, the posterior extremity of the abdomen 

 being held slightly above the surface-film, while the front legs are 

 held some distance below. In this attitude the front legs, slightly 

 bent at the femoro-tibial joint, are extended forward on each side of 

 the head; the femora of the middle and hind legs are extended out- 

 ward at almost right angles to the long axis of the body, while the 

 tibiae of these legs form an obtuse angle with the femora. The front 

 legs are thus in readiness to grab the prey, while the two posterior 

 pairs are ever ready to propel the bug forward instantly at the slight- 

 est disturbance. 



In procuring food, Belostoma does not depend entirely upon the 

 sense of sight. We have often observed a back-swimmer or a water- 

 boatman come to rest on the ventral surface of Belostoma, and were 

 surprised at the number of times the prey escaped. If a back- 

 swimmer or a water-boatman strikes against Belostoma, the latter 

 makes a quick grab for it, and, if successful in capturing it, proceeds 

 to suck out the juices. Often, however, a back-swimmer or a water- 

 boatman is grabbed at as it passes near a Belostoma without coming 

 in actual contact with it. Holmes (23, p. 160) finds that in the young 

 of Ranatra quadridentata, " this action is probably a response to the 

 impact of the water. If a Ranatra is hungry, touching the surface- 

 film with a needle near the insect will often cause it to grab about 

 wildly in the effort to seize whatever may have caused the disturbance." 

 The same experiment was performed with a mature Belostoma which 

 had been starved for a number of weeks, and so rapid was the reac- 

 tion, that only the bug was observed clinging to the needle after the 

 surface-film had been touched with it. Both eyes of a Belostoma 



