September 30, 1897] 



NATURE 



517 



THE SOCIAL SYSTEM OF TERMITES.^ 



THOUGH more than a century has elapsed since 

 Smeathman published the first careful account of 

 Termitidie, but few workers have substantially increased 

 our knowledge of the subject. The reasons for this 

 apparent apathy lie, indeed, on the surface. With few 

 exceptions the Termites are tropical or sub-tropical in 

 habitat ; avoiding light, and living in vast concealed com- 

 munities, their cryptic manner of life renders the task of 

 observation extremely prolonged and arduous, while the 

 multiplicity of forms' in a single species, and the diffi- 

 culties attending their preservation, have earned them 

 little regard from the systematist. 



The first marked advance towards unravelling the 

 complexity of the Termite community was made by the 

 great naturalist so lately lost to science, YnU Miiller. 

 Following out Lespes' observations on the nymphs, he 

 showed that a certain number of Termitidiv reach 

 maturity and propagate without leaving the nest or 

 acquiring the imaginal characteristics, and contended 

 that the function of the swarming adults was not that of 

 founding fresh colonies, but of furnishing royal pairs to 

 pre-existing orphaned nests 



His conclusions were supported by observations in 

 nature, but were not made the subject of experiment ; 

 they are to be regarded as suggestions, which, however, 

 approach very nearly to the truth. 



The subject was taken up by Prof. Grassi in order to 

 investigate the origin of the sterile castes, and the results 

 of seven years' labour have been put forward in a mono- 

 graph which, for the first time, places the nature of the 

 Termite society beyond the reach of speculation. Intri- 

 cate as the memoir is in the presentation of facts and in- 

 ferences, it cannot but leave the reader with a profound 

 sense of the perseverance, fertility in experiment, and 

 deductive ability which it reveals. 



Species of two genera, Calotermes and Termes, were 

 studied, and success was largely due to the fact that it 

 was found possible to keep small numbers of the former 

 genus alive for long periods in corked test-tubes contain- 

 ing rotten wood. Careful observation thus became prac- 

 ticable, and by varying the number and kind of individuals 

 introduced, their development and inter-relations could 

 be studied. 



Grassi's work on Calotermes shows that the eggs are 

 of one kind and the newly-hatched larvae undifferentiated, 

 the caste distinctions arising after birth, and dependmg 

 (in the development of the genitalia. If this proceeds 

 normally, the larva ultimately becomes a winged imago ; 

 if it is arrested at any period before the completion of the 

 nymph-stage, the larva becomes a soldier ; and finally, if 

 it is precociously stimulated, a neoteinic form is produced, 

 one, that is, which reaches sexual maturity without ever 

 acquiring the imaginal characters. The insect remains 

 plastic until the atrophic change of the genitalia has been 

 set up ; thus, a soldier-larva or soldier cannot be modi- 

 fied, but a nymph can be converted into a soldier possess- 

 ing wing-buds (a "nymph-soldier"). These buds may 

 be subsequently reabsorbed, so that a retrogression 

 actually takes place. The colony is headed normally 

 by a single king and queen derived from the perfect 

 insects ; should either or both be missing, their place 

 is supplied by neoteinic "substitute" forms, which are 

 then always produced if the society contains examples 

 capable of undergoing this modification. An orphaned 

 colony may be made to produce a much larger number 

 of substitutes if subdivided into small societies than if 

 kept together, and the same is true of the soldiers. This 

 and «iimilar observations go clearly to show that the 

 modification of these individuals is no way predestined. 



1 " The Constitution and Development of the Society of Termites, &c." 

 By Prof. B. Grassi and Dr. A. Sandias. English translation in the 

 Quarterly Journal of Microuopkal Science, vols. 39 and 40 ; with five 

 plates. 



NO. 1457. VOJ.. 56] 



The insects must possess the faculty for estimating a 

 numerical ratio, and if the number of soldiers or royal sub- 

 stitutes is in excess of their needs, the supernumeraries 

 are killed and eaten ! 



The colony of Termes is more complex and more 

 difficult to study : it is similar in character except that 

 it contains two sterile castes, soldiers and workers, and 

 two kinds of neoteinic forms ; one, the " complementary 

 roval forms" are constantly present in large numbers as 

 the ordinary reproductive members ; the other, the 

 "substitute forms," are developed on an emergency to 

 supply their loss. In Sicily, according to Grassi, the 

 winged imagos are entirely lost after swarming, and 

 never give rise to fresh societies ; but there is evidence 

 that this remarkable example of natural wastefulness 

 is not constantly exhibited in France. According to 

 Marlatt, the closely-allied Termes Jlavipes of North 

 America is known to reproduce by means of comple- 

 mentary forms alone. 



Grassi holds that the caste-modifications are caused 

 by variation in nutriment, and records a series of minute 

 observations on the rather repulsive feeding-habits of 

 these insects, made chiefly by his coadjutor Dr. Sandias. 

 The staple food is wood, passed and repassed through 

 the alimentary canal of several individuals; the society 

 tolerates no waste, and everything of nutritive value, cast 

 skins and dead bodies alike, is greedily devoured. 



Newly-born larvye and forms destined for sexual 

 maturity are fed upon the saliva of their comrades, the 

 largest amount being given to those which are becoming 

 neoteinic ; within forty-eight hours after its adminis- 

 tration they become altered, acquiring ocular pigmenta- 

 tion and a translucent white appearance. 



It is therefore contended that sexual development is 

 directly stimulated by the saliva taken as food ; but a 

 disturbing factor has had to be eliminated. The alimen- 

 tary canal of most Termites teems with protozoa, which 

 bring about the dilatation of a ca^cal ampulla so as to fill 

 the greater part of the abdomen. These protozoa dis- 

 appear under the influence of a salivary diet, and the 

 question has arisen whether the resulting diminution in 

 size of the ampulla may cause the gonads to ripen. Grassi 

 answers this in the negative. All Termites lose their 

 parasitic protozoa at the time of moulting, and by taking 

 advantage of this circumstance he has been able to keep 

 colonies alive for a month or more entirely free from 

 protozoa. A few examples only in these colonies became 

 neoteinic ; and it is therefore clear that the saliva is one, 

 if not the only, necessary factor in bringing about sexual 

 maturity. . 



No light has been thrown on the causes which, in 

 Termes, lead to the differentiation of the soldier from the 

 worker ; but it may be reasonably inferred that they are 

 also due to differences in nutrition. 



As already indicated, the results of this research are 

 directly opposed to the hypothesis that special ova or 

 special sets of "determinants" exist for the various 

 castes in Termitidai. It is not necessary here to dwell 

 upon this point, which, it may be recollected, has been 

 dealt with conclusively by Mr. Herbert Spencer in his 

 controversy with Prof. Weismann {Contemporary Reinew, 

 October 1894). , , , 



The means by which the special characters of the 



sterile castes are inherited is a matter which has caused 



1 Prof. Grassi some trouble. In the original memoir he 



! appears scarcely to have made up his mind on the point ; 



but in a footnote appended to the English translation he 



puts forward the supposition previously advanced by him 



in the case of bees, that it is to be interpreted by the 



\ exceptional occurrence of soldiers and workers capable 



i of oviposition. This view is supported by the discovery 



! of a "nymph-soldier" with well-developed ovarian tubes. 



Much more evidence is still required as to the occasional 



i 



