28 



KNOWLEDGE 



[February 1, 1892. 



one 

 in 0. 



' knot ' 



form. The petiole is raised on its ujiper surface into one 

 or two prominences, which have been called " nodes " or 

 " knots " ; the form of these, and the remarkable outline 

 they give to this part of the insect, can best be seen by a side 

 \ievf (Fig. 2). The presence of these " knots " is one of 



the features by which an 

 i ,c Ant may be recognized 



at once, and more than 

 that, their number will 

 determine to which of 

 our two chief families 

 any given specimen be- 

 longs. Omitting two rare 

 insects which represent 

 the family Porn'ri he, but 

 which are not likely to 

 come in the way of the 

 ordinary observer, and 

 which, for practical pur- 

 poses, may therefore be 

 disregarded here, our 

 British Ants are arranged 

 in two families, the 

 i"i&. 2. — Side view of bodies of (a) Fortiiicida and the 

 Formica rufa, (b) Myrmica rugiuo- Mi/imifida ; the former, 

 dis (C) Pezomachnszonat,,, «,head, ^^^^]^ contains the black 

 0, thorax, c, abdomen, p, petiole, with , , . ,. , 



^np " vnnt. " in A, two in ij, and none and brown species we fand 



in our gardens and streets, 

 having only one " knot," 

 and the latter, which contains the red ones, having two. The 

 petiole is movably jointed to the hinder part of the thorax, 

 and hence the abdomen as a whole can be bent about this 

 joint as upon a hinge. The extra joint in the petiole itself, 

 in the Mi/rwicida', gives still greater mobility to the tiny 

 oval abdomen, at the end of which is situated the sting, and 

 apparently gives these creatures greater freedom in the use of 

 that weapon than if they had only one knot. The Fonnicidcf 

 do not sting, and are satisfied with an abdomen which is 

 not' capable of quite such extended movement. Though 

 they^.do not actually sting, however, they are provided with 

 an abundant supply of poison (formic acid), which they can 

 eject at pleasure, and which is thus instilled into wounds 

 made by the mandibles. If, for example, a nest of the 

 great " Wood Ant," whose huge piles of sticks and frag- 

 ments are familiar objects in woods, be disturbed, a strong 

 smell resembling that of vinegar is perceived, and if the 

 hand be brought near the opening, the insects rear up on 

 their hind pairs of legs, open wide their jaws, tuck their 

 abdomen between the hind legs so that its extremity points 

 forward, and from this eject the poison with great force. 

 The operator's hand soon experiences a smarting sensation 

 resulting from the battery of formic acid brought to bear 

 upon it, and if it then be touched with the tip of the 

 tongue, a sharp sour taste will be observed. Sir .John 

 Lubbock states that he has experienced the effect of the 

 formic acid upon the hand when held at a distance of as 

 much as eighteen inches. If the head be held over a 

 disturbed nest, a little distance above it, the atmosphere is 

 found to be so impregnated with the fumes of the acid as 

 to be almost overpowering, 



Amongst the ichneumon flies and allied insects, there 

 are to be found many species which are wmgless, and which, 

 as they run about on the ground, amongst dead leaves or 

 other rubbish, or over the>fohage of living plants, look a 

 good deal like Ants. They may, however, be distinguished 

 by an appeal to the knotted petiole test. The petiole is, 

 indeed to be found in such insects, as their narrow waist 

 at once testifies, but it has not the characteristic knots, as 

 a glance at the accompanying figure (Fig. 2) will show. 



The insect whose body is represented in profile, and a 

 portrait of which is given in Fig. 8, is a parasite on spiders, 

 and has no connection with Ants, leading as different a life 

 as could possibly be imagined. 



The second feature of importance in distinguishing Ants 

 from other insects is to be found in the antennte. These 

 are always of the same type. There is a little roundish 

 joint by which they are attached to the head in the front of 

 the face (Fig. 1). This is succeeded by a long slightly- 

 curved shaft, occupying about a third of the length of the 

 whole antenna ; this is called the " scape." This, again, 

 is succeeded by a string of small joints, the number of 

 which depends upon the species and the sex ; sometimes 

 these increase in width a little before the tip, and so 

 give a club-shaped appearance to this flexible part, 

 which, from its flexibility as contrasted with the stiffness 

 and rigidity of the scape, has been called the " flagellum " 

 {Latin — whip), the lash, of which the scape is the 

 handle. Now, bees and wasps also have antennje 

 constructed like this, but as they are never wingless, 

 they are not likely to be mistaken for Ants, notwithstand- 

 ing their " elbowed '' antennse. A greater difficulty wiU be 

 felt in distinguishing winged Ants from wild bees, but here 

 the scale or knot on the petiole will come to the student's 

 assistance and settle the matter. If we look now at those 

 other wingless Hymenoptera which are not Auts, we see that 

 this antennal feature may again be used as a means of 

 discrimination. It is true that in such insects the second 

 oint of the autennse is a good deal longer than any of the 

 rest, and sometimes (especially in the very small species) 

 even as long as in the Ants. In such 

 cases the knotted petiole test must 

 be applied. But in many instances 

 the second jomt is not nearly so long 

 as in the Ants, and then the many- 

 jointed terminal part is not placed 

 at an angle to the rest, so that the 

 antennie do not become " elbowed" 

 ( Fig. 3 ) . This is more evident in the 

 living insect than in the dead one. 

 The Ant's antennte are carried 

 pointing forwards, but with the 

 flagellum set at an angle to the 

 scape, like a human arm bent at the 

 elbow, and then the whole organ 

 and its two chief parts can be 

 placed in the same variety of posi- 

 tions as the arm which it imitates ; 

 the antenna; of the Pc^niiiachm 

 above-mentioned, and other para- 

 sites are not carried bent in this 

 way, but straight forward, and their tips are maintained in 

 an incessantly quivering or vibrating condition, as the insect 

 goes on its way. It is astonishing what difi'erences of expres- 

 sion can be imparted to the head by the varying positions of 

 the antenuiE. The importance of this is seen when we bear 

 in mind that an Ant's head, like that of any other insect, 

 is covered with a hard, unyielding skin, any movement in 

 which is absolutely impossible : all expression of the 

 emotions, therefore, must be restricted to the movement of 

 external parts, like the jaws and antenuse, and to the 

 varying positions of the head itself; in fact, nothing more 

 devoid of expression can be imagined than an Ant's head, 

 apart from the jaws and antenna- ; the fixity of the eyes 

 and the bloated appearance of the head itself make it look 

 as unmtellectual as the helmet of a diver. And yet this 

 expressionless object can have a strong semblance of an 

 air of war-like courage and bold defiance, of intelligent 

 appreciation and aft'ectionate sympathy, of industrious 



Fig. 3. — Pezumachus 

 :onatiis, a parasite on 

 sjjiders ; not an Ant. 



