1V.-ANTS IN THEIR DIVERSE RELATIOSS TO THE PLANT WORLD BY J. BEQUAERT The following contribution is an attempt to summarize what is known at present of the widely varied and often intricate relations which exist in nature between ants and vegetation. It has primarily grown out of an examination of certain so-called ‘‘ myrmecophytes,” or ant-plants, which I frequently came across during my travels in the Belgian Congo in quest of zoological and botanical specimens. Prof. Wheeler’s study of the feeding habits of the larva of certain plant-inhabiting ants col- lected by Messrs. H. Lang and J. P. Chapin and myself in the Congo, and Prof. I. W. Bailey’s investigation of the anatomy of myrmecophytes show that the whole subject of the mutual adaptations of plants and ants is in need of a thorough revision. It thus seemed appropriate that the present opportunity be used to bring together the many isolated and scattered observations which have been made on the interrelations of these organisms. Indeed, the problem of myrmecophytism is dominated by the feeding habits of the ants and their young and, until these are perfectly understood, we can scarcely hope to grasp the true ecological meaning and the probable origin of the extreme cases of apparent or true symbiosis between certain ants and certain species of plants. It is, therefore, of the utmost importance to inquire carefully into the various ways in which ants are wont to benefit by the vegetation. Although much time has been spent in consulting botanical and entomological papers for information bearing on the subject, undoubted- ly a number of interesting observations have escaped my notice. In keeping with the general purpose of the present contribution to African Myrmecology, especial attention has been paid to work accomplished in the tropics, primarily in Africa. The bibliography appended to this part is as complete as possible. In it are included many papers which may seem to have but remote connection with the subject-such as, for instance, those on fungus-growing termites, intracellular symbionts, and the like. I believe, however, that they are indispensable in reference to the study of certain activities of ants. Some students may find the botanical side rather too fully treated, but this seemed unavoidable in providing the necessary background for future field work, especially to the myrmecologist. Moreover, I am convinced that the ultimate solution of many of the problems involved can only come from a close cooperation between botanical and entomological experts, and this, under present conditicns of specialized training, is not so easily realized. a33 334 Bulletin American Museum of Xatural History [VOL XLV Many of the data here presented were brought together during the several weeks I had the pleasure of spending at the Bussey Institution for Applied Biology of Harvard University. I wish to thank President Henry Fairfield Osborn and the authorities of The American Museum of Natural History for the liberal manner in which I have been able to carry on this work. I am also under great obligations to Professors Wm. M. Wheeler and I. W. Bailey, of Harvard University, for their many suggestions and criticisms during my stay at the Bussey Institution. The interest they have shawn in the work has been a steady encourape- ment and their advice invaluable. 1. VARIOUSRELATIOSS BETWEET ANTS AND VEGETATION Economic Importance of Ants The question whet'her ants are, broadly speaking, noxious or bene- ficial insects is still debated by agriculturists and economic entomologists. While it is believed on the one hand that ants attack and mine only sick and de- caying plants, especially decaying roots, on the other hand it is claimed that healthy plants, which show no trace of disease, are also assailed by ants. In any case further exact observations concerning the relation of ants with plants will he needed in order to clear up this problem. The elucidation of the question of the direct nosi- ousness of ants to plants is the more desirable, since we possess in the ants partly a welcome help against other animal enemies of culture-plants, which they pursue and destroy. It is therefore necessary that we learn more in detail whether their harm- fulness outweighs their utility or vice versa. In general onr ($anperhaps say that, judging from statements which have been made thus far, their noxiousness to plants, by attacking roots, stems or branches, is not very great. (G. Aulmann and IV. Ln Baume, 1912, p. 61.) In their recent study on the feeding habits of ants, Wheeler and Bailey (1920, p. 236) have pointed out that one reason why the economic importance of many common ants remains so dubious or ambiguous is the lack of preclse information with regard to the quality and quantity of their food, especially in the larval stage. These authors have shown, for instance, that ants carry on their bodies and in the food-pellets of their infrabuccal pockets an extraordinary number and variety of fungus spores and bacteria. It is, therefore, quite possible that these insects have a great but hithert'o only vaguely apprehended importance as carriers of the gems of certain plant, animal and human diseasce. That ants are active carriers of pathogenic micro-organisms has been further suggested by Darling (1913) , Wheeler (1914), Studhalter and Ruggles (1915), Grabham (1918), and Bailey (1920). 19221 Ii‘hreler, ants of the Belgian Congo 335 The leaf-cutting ants of the tribe Attini, so abundant in tropical and subtropical America, are decidedly destructive to the vegetation and are rightly considered one of the worst pests to South American agricul- ture. Accounts of their depredations are found in practically all narra- tives of South American travellers. Though they attack many of the native herbs, shrubs, and trees, they often show a predilection for cul- tivated plants. It is no uncommon thing to find the sadvas, Atta cephalotes (Linnseus), so numerous in certain spots that the planters are forced to abandon their fields. Speaking of the ants in the Brazilian coffee districts, Van Delden (1885, pp. 297-298) writes: “The enemy most dreaded in the fazendas (plantations) is indubitably the sadva. or tana-jura, a dark-brown ant, two centimeters long, which undermines the ground by digging extensive passages and dens in all directions. It attacks all sorts of trees the coffee-shrub among others, but has a decided preference for the orange and citron trees in the coffee gardens.” H. W. Bates (1863) and others have noted that these ants often become troublesome to the inhabitants because of their habit of plundering the stores of provisions in houses at night. The Attini are not represented in the Old World tropics, but pos- sibly ants of other groups have developed similrr habits there, though on a smaller scale. G. Aulnianii (1912, p. 156) and Moorstatt (1914) mention that a leaf-cutting ant was observed in German East Africa at times causing considerable damage to cotton plants. The specific iden- tity of this ant has not been ascertained, but it probably belonged to the genus Messor, which is known to collect pieces of grass in addition to seeds and grain (see Piostedt’s observation quoted below, p. 359). King (1911) also notes that Messor barbarus (Linnseus), at Khartum, damages garden plants by biting off and carrying away the leaves, and adds that in cotton fields the sites of their nests are marked by bare patches devoid of vegetation. What use these ants make of the vepe- table matter thus carried into their nests has not been investigeted. There are a. few other cases on record of ants directly destroying living parts of plants. It is generally known that certain ants will injure buds and fruit in order to feed on the exuding sap (see Muller-Thurgau, 1892, pp. 134-135). Fore1 (1885, p. 338) mentions instances of Tetra- morium crespitrm (Linnzus) attacking young roots of healthy sugar- beets at Thus, Switzerlniid, many of the plants dying from the injurier received. J. P&ez (1906, pp. xxxii-xxxiv) records the havoc played by the same ant on the tubers of potato, near Bordeaux, more or less deep cavities heing excavated and many young plants killed; T. czspitu?~ 336 Bulletin American Museum of A-atural History [Vol. XLT’ was also found burrowing superficial galleries in the stems of living potato plants and attacking the roots of young cabbage and carrot.’ In North America, Solenopsis geminata (Fabricius) and S. molesta (Say) often do injury to the soft parts of planted seeds, and the former also to strawberries (Webster, 1890) and other fruit. S. molesta has proved very injurious in gardens and fields; the chief damage is done to seeds of sorghum and corn, which are hollowed out undoubtedly for the purpose of extracting the oils (McColloch and Hayes, 1916; Hayes, 1920). According to Green (1900a) and G. R. Dutt (1912, p. 247), the Indian Dorylus orientalis Westwood is mainly or exclusively herbivorous, feed- ing on the bark of trees and the healthy tubers of plants, a habit the more remarkable since the majority oi Dorylinze are highly carnivorous. In Cameroon, certain ants have been seen attacking the fruits of cacao- trees : Camponotus maculatus subspecies brutus (Forel) gnaws the base of fruit-stalks where they are inserted into the trunk, licking up the sap at the wound, causing the fruits to drop off or dry; Crematogaster africana variety winlcleri (Forel) gnaws away the skin of the cacao-fruit, often almost completely; while Camponotus acvapimensis Mayr and CEcophylla longinoda (Latreille) are accused of the same evil, though they cause but little damage (H. Winkler, 190.5, pp.