MOTIONS OF INSECTS, 453 



use, the insect cannot leap more than six inches. 1 The 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 remark- 

 able horn looking towards the anus, which arms their posterior hip. Some 

 bugs that leap well, Acanthia saltatoria, &c., seem to have no particular ap- 

 paratus 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 1 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 celebrated Evelyn in his 

 Travels. When at Rome, he often observed a spider of this kind hunt- 

 ing the flies which alighted upon a rail on which was its station. It kept 

 crawling under the rail till it arrived at the part opposite to the fly, when 

 stealing up it would attempt to leap upon it. If it discovered that it was 

 not perfectly opposite, it would immediately 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 back- 

 wards, 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 distance, swift 

 as lightning she made the fatal leap and secured her prey. 2 I have had an 

 opportunity of observing very similar proceedings in Salticus ^cenicus. 



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

 numerous species of the elastic beetles (Elatcr), 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 bases 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 basis of the inter- 

 mediate legs, you will discover in the after-breast (ppstpectut) 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 



1 De Geer, iii. 178. 



3 Evelyn, quoted in Hooke's Mlcrogr. 200. 

 GG 3 



