488 MOTIONS OF INSECTS. 



species of another genus of the homopterous Hemiptera (^Chermes), that 

 jump very nimbly by pushing out their shanks, are perhaps assisted in this 

 motion by a remarkable liorn looking towards the anus, which arms tlieir 

 posterior hip. Some bugs that leap well, Acanthia saltatoria, he, seem 

 to have no particular apparatus to assist them, except that their posterior 

 tibiae are very long. Several of the minute ichneumons also jump with 

 great agility, but by what means I am unable to say. There is a tribe of 

 spiders, not spinners, that leap even sideways upon their prey. One of 

 these (^Salticus scenicus), when about to do this, elevates itself upon its 

 legs, and lifting its head seems to survey the spot before it jumps. When 

 these insects spy a small gnat or fly upon a wall, they creep very gently 

 towards it with short steps, till they come within a convenient distance, 

 when they spring upon it suddenly like a tiger. Bartram observed one of 

 these spiders that jumped two feet upon a humble-bee. The most amusing 

 account, however, of the motions of these animals is given by the cele- 

 brated Evelyn in his Travels. When at Rome, he often observed a spi- 

 der of this kind hunting the flies which alighted upon a rail on which was 

 its station. It kept crawling under the rail till it ariived at the part oppo- 

 site to the fly, when stealing up it would attempt to leap upon it. If it 

 discovered that it was not perfectly opposite, it would inunediately slide 

 down again unobserved, and at the next attempt would come directly 

 upon the fly's back. Did the fly happen not to be within a leap, it would 

 move towards it so softly, that its motion seemed not more perceptible than 

 that of the shadow of the gnomon of a dial. If the intended prey moved, 

 the spider would keep pace with it as exactly as if they were actuated by 

 one spirit, moving backwards, forwards, or on each side without turning. 

 When the fly took wing, and pitched itself behind the huntress, she turned 

 round with the swiftness of thought, and always kept her head towards it^ 

 though to all appearance as immovable as one of the nails driven into the 

 wood on which was her station : till at last, being arrived within due dis- 

 tance, swift as lightning she made the fatal leap and secured her prey.^ 

 I have had an opportunity of observing very similar proceedings in Salticus 

 scenicus. 



But the legs of insects are not the only organs by which they leap. 

 The numerous species of the elastic beetles (tllater). skip-jacks as some 

 call them, perform this motion by means of a pectoral process or mucro. 

 These animals having very short legs, when laid upon their backs, cannot 

 by their means recover a prone position. To supply this seeming defect 

 in their structure. Providence has furnished them with an instrument which, 

 when they are so circumstanced, enables them to spring into the air and 

 recover their standing. If you examine the breast (pectus) of one of 

 these insects, you will observe between the base of the anterior pair of 

 legs a short and rather blunt process, the point of which is towards the 

 anus. Opposite to this point, and a little before the base of the interme- 

 diate legs, you will discover in the after-breast (postpecius) a rather deep 

 cavity, in which the point is often sheathed. This simple apparatus is all 

 that the insect wants to effect the above purpose. When laid upon its 

 back, in your hand if you please, it will first bend back, so as to form a 

 very obtuse angle with each other, the head and trunk, and abdomen and 



* Evelyn, qaoted in Hooke's Microgr. 200. 



