COLEOPTERA DYTICID^. 97 



plates or alulets, which Dufour considers produce the humming noise 

 which these insects have the power to make. The wings, which are 

 hirge, exist in all the species. The spiracles are eighteen in number, 

 the first pair being situated between the pro- and mesothorax, the second 

 between the metathorax and first abdominal segment, and the seven 

 remaining pairs upon the second to the eighth dorsal segments of the 

 abdomen. 



The Dyticidae are found in all quarters of the globe, inhabiting 

 stagnant in preference to running waters. They swim with great 

 agility, the hind legs acting together in concert like those of a frog, 

 the antennae at the same time being erected, and the palpi concealed. 

 (^New?nan, in Snf. Mag. vol. i. p. 315.) They are very voracious in 

 their habits, attacking and devouring not only other aquatic insects, 

 but are also occasionally very destructive to young fish in fish-ponds 

 (Vide Mag. Nat. Hist. No. 12.). Mr. Anderson, the curator of the 

 Chelsea Botanic Gardens, has also informed me that he has suffered 

 much from these insects attacking young gold and silver fish, eating 

 their dorsal and pectoral fins. Dr. Burmeister also mentions that a 

 specimen of Cybister Roselii which he kept, devoured two frogs in 

 the space of forty hours, and nevertheless, when he dissected it 

 shortly afterwards, it was found to have entirely digested them, the 

 intestinal tube being empty. They are very fearless in their attacks, 

 seizing insects much larger than themselves. A specimen of Dyt. 

 marginalis, which Esper kept in water alive for three years and a half, 

 feeding it with raw beef, is recorded by Clairville to have destroyed 

 a specimen of the large Hydrous piceus (although twice its own size) 

 piercing it with its jaws on the only vulnerable point, viz. on the 

 under side, at the insertion of the head in the thorax, and sucking its 

 juices. Messrs. Kirby and Spence endeavour to account for the extra- 

 ordinary duration of life of this specimen by supposing that it was caused 

 by the celibacy of the insect. (See also Mag. Nat. Hist. No. 12. for 

 observations on the tenacity of life exhibited by these insects). They 

 employ their fore legs as claws in seizing and conveying their prey to 

 the mouth ; and Dr. Esper observed that his D. marginalis so com- 

 pletely sucked the blood out of the bits of meat with which he fed it, 

 that they appeared only like small white masses floating in the water. 

 Dr. Erichson, however, states that those which he kept alive refused 

 to cat flesh, neither would they feed upon their companions unless 

 one happened to die ; and one, which De Geer kept, died in consequence 



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