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A Study of the Weaver , (Fab.)1 Author(s): A. C. Cole, Jr. and J. W. Jones, Jr. Source: American Midland Naturalist, Vol. 39, No. 3 (May, 1948), pp. 641-651 Published by: The University of Notre Dame Stable URL: http://www.jstor.org/stable/2421529 . Accessed: 17/07/2013 13:17

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This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions A Studyof theWeaver Ant, Oecophyllasmaragdina (Fab.)'

A. C. Cole,Jr. and J.W. Jones,Jr. Departmentof Zoology & Entomology, Universityof Tennessee,Knoxville

Recentattention to certainants of theAsiatic fauna has directedparticular intcresttoward the Oecophylla;2specifically, to Oecophyllasmaragdina (Fabricius). In reviewingavailable papers on the species,and in our investiga- tionsof collectedmaterial, certain features have seemednoteworthy. Also, we were made aware of the scarcityand remotenessof literatureconcerned with this most interestinggenus. For these reasons,in presentingrecent observa- tions,a generalreport on the genus is included,although particular referenco is devotedto Oecophyllasmaragdina. .-The following descriptionof the genus is taken frorm Wheeler'sreport on the of theBelgian Congo (1922). "Worker medium-sized,slender, slightly polymorphic. Head ratherlarge, broader behindthan in front,with rounded sides and posteriorcorners and semicircularlyexcised occipitalborder, very convex above. Eyes large, convex,broadly elliptical,situated in frontof the middle of the head. Ocelli absent. Palpi very short,maxillary pair 5- jointed,labial pair 4-jointed.Mandibles long and large,triangular, with nearlystraight lateralborders, a verylong curvedapical toothand numerousshort denticles along the straightapical border.Clypeus very large and convex,but not distinctlycariini"te, its anteriorborder entire or very feeblysinuate in the middle,depressed and projecting overthe bases of the mandibles.Frontal area ratherlarge, subtriangular; frontal carinae moderatelylong, subparallel. Antennae very long, 12-jointed,the scapes insertedsome distancefrom the posteriorcorners of the clypeus,rather abruptly incrassated at their tips; the firstfunicular joint very long and slender,longer than the second and third together,joints 2 to 5 muchshorter, subequal, slender, the remainingjoints except the last, shorterand distinctlythicker. Thorax long and narrow; pronotumlonger than broad, evenlyconvex above, narrowedand colliformanteriorly; mesonotum anteriorlv long and constricted,subcylindrical, suddenly broadenedbehind where it joins the small, short,unarmed epinotum, which is roundedand convex above and withoutdis- tinctbase and declivity.Petiole long and slender,much longer than bioad, subcylindri- cal, with a very low roundednode near its posteriorend, its ventralsurface near the middlemore or less convex,its posteriorborder on each side witha small rounded,pro- jectinglamella, appearinglike an acute toothwhen the segmentis viewed fromabove. Gaster short,broadly elliptical, its firstsegment suddenly contracted to the petiole,the tip ratherpointed. Legs very long and slender; claws, pulvilli,and last tarsal joint enlarged.Gizzard with long slender sepals, which are not reflectedat theiranterior ends."

I Contributionno. 16, Dept. of Zoology& Entomology,Univ. of Tenn. 2 Described by F. Smith,Journ. Proc. Linn. Soc. Lond., Zool., Vol. 5, p. 102, 1861. 641

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 642 THE AMERICAN MIDLAND NATURALIST 39 (3)

Taxonomically,the genus consistsof two distinctspecies with theirsub- speciesand varieties.One of theseis Oecophyllasmaragdina (Fab.) withtwo subspecies,subnitida Emery and virescens(Fab.) and withits threevarieties, selebensisEmery, gracilior Forel and gracillimaEmery. The otherspecies is Oecophyllalonginoda (Latreille) withfour varieties: textor (Santschi), rubri- ceps (Forel), annectansWhlr. and fusca (Emery). These membersof the genusare easilyseparated by Wheeler'skey (1922) as follows:

1.Petiole very slender, its stigmataseen fromabove very prominent, its ventral surfacenearly straight or veryfeebly convex in profile(smaragdina) - 2 Petiolestouter and higher, its stigmata seen from above not prominent, itsventral surfacestrongly convex in profile(longinoda) .---7 2. Body ferruginousor testaceous -3 Gasterand sometimes the head pea-green, head more rouinded and lesstruncated behind;size smaller,petiole somewhat shorter (Queensland, New Guinea,the IslandsAru and Key)-subspecies virescens(Fab.) 3. Integumentopaque or subopaque -4 Integumentmore or lessdistinctly shining -5 4.Color ferruginotis(, Ceylon, Cochin China, Indonesia) -smaragdina (typical) Smallerand more testaceous, mesonotum and petiole a littlenarrower (Java). -- .-- var. graciliorForel 5. Largeforms, integument slightly shining (Papua, Philippines,Melanesia). ------subspeciessubnitida Emery Smallerforms, integument more shining --6 6. Bodyvery shining and slender, color testaceous, head rather elongate . ------.. var. gracillimaEmery Less shiningand less slender, head shorter (Celebes) - var.selebensis Emery 7. Ferruginousor testaceousthroughout -8 Brownor black------9 8. Color ferruginous(West Africa)-longinoda (typical) Colorpaler, more testaceous, petiole shorter, head slightlybroader, apical tooth of mandiblesshorter (Zanzibar) -var. textor(Santschi) 9. At leastthe thorax and mandiblesblack - 10 Bodyrather uniformly brown (Belgian Congo) .------var. annectensWheeler 10.Head dullred, gaster often brownish (Belgian Congo) - var.rubriceps (Forel) Head and gasterblack or darkbrown (Belgian Congo, Nigeria, Liberia, Cam- eroon,Spanish Guinea) ------var. fusca (Emery)

Distribution.-A tabulationof recordsshows that the genus is confinedto the Old World Tropics,ranging over the Indo-Malayan,Papuan and Ethio- pian regionsbut does not occurin Madagascar. 0. smaragdina,with its sub- speciesand varieties,ocurs in the Ethiopianregion. At one pointin his discus- sion Wheeler remarks,"Several authorshave cited the true smaragdinafrom east Africa.Unfortunately I have littlematerial from that regionand what I have is certainlylonginoda, presumably belonging to textor,though this variety seemsto me to be poorlycharacterized and possiblynot distinctfrom the typical formof the species.I am unableto say,therefore, whether Oecophylla smarag- dina actuallyoccurs on the AfricanContinent."

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Dr. M. R. Smith3 has stated that he believesthe formmost commonly recordedfrom to be Oecophyllasmaragdina in the broad sense and hlaskindly furnished us witha specimenof the subspeciesvirescens in the cot- lectionof Pergandeand bearingthe localitylabel "CentralAustralia." Dodd (1902) has collectedthe species in Australiaand has reportedon Notes on the QueenslandGreen Ant,doubtless in referenceto Oecophyl- la smaragdinasubsp. virescens. D6flein (1905) gives interestingacocunts of the speciesfrom Ceylon and mentionsrecords from western India at Bombay. Mr. FredricSmith (1864), past assistantin zoologyat the BritishMuse- um, listedOecophylla smaragdina from the islandsof the EasternArchipelago; specifically,the islands of Mysol, Timor, Waigion; Gilolo; Bachian; Dory; Aru; Borneo;the Philippines;and fromJava, these records constituting a part of tlle reporton theHymenoptera collected by Mr. A. R. Wallace in the East- ern Archipelago.In a followingreport (1864) Smith adds Malacca, China, Celebes and Sumatra.He furtherstates: "I have considerabledoubts of its (0. smaragdina) being really specificallydistinct from the African species Oecophyllavirescens, which also occursin Australia." Other writershave referredto the "red treeant" of the old worldtropics and have listedthe genusfrom Australia, India and Africa. Although Forel (1894) states, ". . . Oecophyllasmaragdina, one of the most common ants of tropical Africa . . .," it can now be shown that this speciesis not knownfrom the Ethiopianregion, longinoda being restrictedto the continentof Africaand, in all probability,the speciesto whichForel has reference. Other recordsof distributionof the genus includeWeber's (1946) speci- mens of 0. longiniodafrom the Belgian Congo, Mafia Island, Tanganyika, the Sudan, West Africaand Akkra. In addition,Keuchenius (1914) reports 0. smaragdinafrom Java. Colonel Bingham (1903) recordsthe species from the whole of India, Burmaand Ceylon exceptin the desertand treelesstracts, also listingthe ant fromAustralia and New Guinea. It is interestingto note that fossil formsrepresenting four species of Oecophylla are to be found in European Tertiarydeposits. 0. brischkeiis knownfrom Baltic amberand 0. sicula fromthe Sicilianamber deposits" both of the early Oligocene age and both species closely related to smaragdina. These constitutethe only known fossilrecords of the genus,indicating that presentday distributionsare relicts,probably due to formerland connections. Biology.-The genus Oecophylla,together with two other genera (Cam- ponotus and )of the same subfamilyare unique among ants in thatsome of the speciesconstruct nests largely made up of producedby the larvae,in whichcase the larvae themselvesare used as tools. In the case of both Oecophyllalonginoda and smaragdinathe larvaeare utilizedas "shut- tles" held by the mandiblesof the minimaworker caste in fasteningleaves togetherinto a nest. Here then,is a case in which the larvae are actually

3 By personalcorrespondence.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 644 THE AMERICAN MIDLAND NATURALIST 39 (3) knownto producesilk, but the pupae of theselarvae are alwaysnude. In each instanceit has been observedthat only immaturelarvae are utilizedin produc- ing the silk used in nest constructionand that the well developedlarvae are not utilizedin producingthis material. The nests of 0. smaragdinaare generallyconfined to the scrubsand not commonlyfound in the forestproper. The speciesis polydomousand nestsof varyingsizes form"patches" in treesof whichthe foliagemay be sparse (See Fig. 2). Frequentlythe old nestsmay be abandonedwhen the leaves become withered.No queens or wingedforms were presentin any of the nestsexam- ined noi' was a winged individualfound among the hundredsof specimens collectedin India, althoughlarvae were presentin relativeabundance. Dodd (1902) has written:"It -is astonishingwhat myriadsof inmatesthese nests contain;many of the chambersappear to be almost filledwith the ants and theirpupae and larvae.A new nestmay be tornopen, and thoughmany larvae are present,no queen can be discovered;perhaps the queen may live in ; centralnest .... " Later Dodd (1902) asks the question,"Do queens live any lengthof time,or do theydie at the approachof winter,leaving enough eggs to supply larvae to the severalcolonies for some weeks or even months?"In anotherpaper (1902), thissame authorstates: "During the wetseason, queens

Fig. 1.- A map of the east showingrange of the genlus Oecoplsyllaand its fossil species.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 1948 COLE ET AL.: A STUDY OF THE WEAVER ANT 645 may be found singlythroughout the scrubsin littleretreats formed by few leaves." The nestsexamined by the seniorauthor represented myriads of all sizes and positions,including the succursalsand shelterssome distancefrom the nest,yet the grass-greenfemales and the blackmales werenot found.

Fig. 2.-Nests of Oecophylla smaragdinain ,Upper Assam, India. Photo by A. C. Cole, Jr

Fig. 3-Typical nest of Oecophiyllasmaragdina. Photo by A. C. Cole, Jr.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 646 THE AMERICAN MIDLAND NATURALIST 39 (3)

It is interestingto note that food is not storedwithin the nest of the species but that the ants do tend , feedingupon the exudates of the scales, and also commonlyattend Lycaenid larvae. Frequentlythe larvae and aphids may be found withinshelters constructed in the same fashionas the primarynests and approximateto these nests. Indeed, Keuchenius (1914) holds the view that Oecophylla smaragdinais verynoxious to coffeeplanta- tions throughits habit of-keeping and protectingin its neststhe greencoffee scale, Lecanium-viride, a mostserious of the coffeetree.

The workersdo not possess a stingbut are neverthelessvery effective in defendingthemselves and the nests frominvasion by the instinctivepattern of bitingrather severely and thenejecting a "spray" of formicacid fromthe tip of the abdomen,the gasterhaving been tumed forwardbeneath the head and directedto the area of the bite.

Dimorphism.-The observationspublished by Weber (1946) concerning dimorphismand possiblecaste divisionamong workersof the Africanspecies longinoda,were concurrentwith similar observationsof the impressivesize variationin workersof the Asiatic species collectedby the senior author in the interiorprovince of Assam in northeasternIndia during1943 and 1944. Moreover,it had been notedthat Wheeler (1910) referredto the workersof the genus as "monomorphic,"yet postulateda possibledivision of labor: "A remarkableexample of divisionof labor,without corresponding structural dif- ferentiation,is seen also in the Oecophylla,an ant which inhabitsnests of leaves sewn togetherwith finesilk. Accordingto the observationsof Dodd (1902) and Doflein (1905), whenthe nestsare tornapatt the monomorphic workersseparate into two companies,one of whichstations itself on the out- side of the nest,draws the separatedleaves togetherand holds them in place with the claws and mandibles,while the other moves the spinninglarvae back and forthwithin the nesttill the rentis repairedwith silken tissue." Still moreinteresting is the directspeculation of D6flein (1905), whichthe authors have translatedas follows: "We saw that an interestingdivision of labor betweenthe differentindividuals of the Oecophyllaenables themto carryon a surprisinglyartful building activity. Is it not possible that all individuals take over in the differentroles, or do we finda differentiationof the instincts in special individuals?Do we findthat theyare actuallymorphologically dif- ferentiated?That is, are thereworker castes which we can distinguishby their morphology,each of whichis associatedwith a specialtask? I was made aware of thispossibility by questionsduring a lecturebecause the materialwhich was put on exhibitionduring the lectureshowed small workersas bearersof the larvae and also, side by side, the largeworkers. Actually it can be shownfrom the materialwhich comes fromone nest that a noticeablesize differencebe- tweenthe various workerindividuals does exist. Also, it was verynoticeable that all individualswhich still held larvae betweenthe mandiblesin death, weresmall individuals.I also rememberthat during my observationsI noticed particularlythat therewas a differenceof size of the individualswhich held the leaves togetherand of those whichacted to defend the nests. It might,

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 1948 COLE ET AL.: A STUDY OF THE WEAVER ANT 647 therefore,be possible that such differences are actualities,and I shouldlike to begfuture investigators to observe if specialindividuals have the task (1) of lholdingthe leaves, (2) of weavingwith larvae, (3) defense,(4) of collecting honeyfrom aphids. It wouldbe veryeasily possible that the size differences observedby myself are accidental." Withthese accounts brought to lightin searchingthrough the scant litera- tureon thesubject, it has beenthought worthwhile to followup speculation withactual facts in so faras thepreserved material might be utilized.First of

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Fig. 4.-Graph showingthe bimodalcurve obtainedfrom thoracic measurements of 88 antsf rom NEST]1. The brokenline gives a plotwhen measurements were adjusted to 1/10 mmfrequency and thecontinuous line indicates a plotof thesame series ad- justedto 1/5mm. frequency. Actual measurements were made to 1/100 mm.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 648 THE AMERICAN MIDLAND NATURALIST 39 (3) all, was thereactually a dimorphiccondition in the workersof 0. smaragdina and if so werethere actual morphologicaldifferentiations? With thisview in mind,and followingthe approachset by Weber (1946) I was decidedto measurethe randomsamples of two colonies (one large,the othersmall) and to see if the apparentsize differencewas a gradual inter- gradationrepresenting extremes from a mean average,or to observeif two size groups were involvedand, if so, how sharplydivided the two "castes" mightbe. It was apparentthat an overallmeasurement of each ant would not yield an accuratealgebraic curve because of variableextensions of the gaster

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16 20 28 3.4 MEASUREMENTS IN MAMt Fig. 5.-Graph showingthe bimodal curveobtained from thoracic measurements of 674 antsfrom Nest 2. These plotsare constructedon thesame basis as in Fig. 4.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 1948 COLE ET AL.: A STUDY OF THE WEAVER ANT 649 due to preservation.On thisbasis, a measurementof the overallthorax length was used, since the relativeshape and extensionof this body regionwere con- stant,and an accuratecorrelation of thislength to body lengthwas established. All specimenswere soaked overnightin warm 50% alcohol, becoming somewhatflaccid so that appendages lay in a natural position. Measure- mnentswere made by a reticlemounted in a binocularmicroscope. All meas- uretnentswere to 1/100 mmn.for close accuracy,and translatedto the graphs figured.Only workerswere used and the resultsare summarizedas follows:

NEST ONE: Of a total of 88 ants from this small n1est,measurements gave a very decided bimodal curve which shows two distinct size groups with no overlap. From this nest, 34 ants are represented as minima and 54 as maxima. Extremes for the minima ants are from 1.26 mm. to 1.98 mm. with the greatest frequency lying at 1.50 mm. Maxima extremes are from 2.21 to 3.30 mm. with the greatest frequency at 2.60 mm. The overall extremes for the nest, then, are from 1.26 mm. to 3.30 mm. as faT as the thoracic measurementsare concerned.

NEST Two: Of a total of 674 ants taken from this nest, two size groups are shown by a clear bimodal curve. From this nest, 163 ants are represented as minima and 511 as maxima. Extremes for the minima of this nest are from 1.29 mm. to 2.01 mm. with the mode lying at 1.60 mm. Maxima extremes are from 2.16 mm. to 3.30 mm. with the

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Fig. 6.-A graphic total of all ants measured to show the general trend of the workers of the species.

This content downloaded from 128.103.149.52 on Wed, 17 Jul 2013 13:17:47 PM All use subject to JSTOR Terms and Conditions 650 THE AMERICAN MIDLAND NATURALIST 39 (3) greatest frequency at 2.65 mm. The overall extremes for individuals of this nest, then, are from1.29 mm.to 3.30 mm.,an essentialduplication of size rangein nest 1. Conclusions regardingsize range are indicative.If, as mentioned,the workersof the species were not dimorphic,one would expect to find, on measurement,a normalfrequency curve, the singlemode of whichwould rep- resentthe typicalsize and the extremesindicated by the sides of the curve. However,the bimodalcurve found in measurementsof 0. smaragdinashows rwo distinctsize groups. An ant of this species selected at random,then, would be eitherof the maximaseries or of the minimaseries. The variation fromthe minima mode mightbe expectedto overiap the variationof the maximamode, but suclhdid not occur in the seriesto any appreciableextent. Only a singleindividual fell betweenthe adjacentextremes of the castes and, morphologically,this specimencompared with the minimaseries. It should also be mentioned,in view of D6flein's observations,that threeants of the minimacaste held larvaein theirmandibles. Morphologically,tlhere were found to be certainconsistent characteristics whichwill differentiateone workercaste fromthe otler. Neglectingthe very evidentsize factor,one can correctlystate that membersof the minimacaste are more obviouslycompact and thickened,whereas the largercaste may be characterizedby its lonlgand slenderform. The followingtable lists compara- tive featuresof six structuresbased on actual inspectionof twenty-fivespeci- mensfrom each caste:

A. MAY/MA WORKER

a M/N/MA WORKER

Fig. 7.-Contrastingfeatures of the maxima worker (A) and the minimaworker (B) as seen in profile.(Camera lucida drawingsfrom typical specimens.)

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Minima Maxima

Antennal Never as long as the Always as long as or longerthan Scape head, not includingthe thehead includingthe mandibles. mandibles. Clypeus More convex than in Less convexbut still not flattened. maxima. Mandibles T e r mi n a I tooth not Terminaltooth very prominent. markedlyprominent. Pronotum Spherical: m u c h m o r e Longer: not as markedlyconvex convex when viewed in when viewed in profile. profile. Mesonotum Not elongated: niot cy- Slender: cylindrical:on the aver- lindrical: taperinguni- age, threetimes as long as the formlyto the posterior constrictedwidth. margin. Petiole Never as much as three Always at least fourtimes as long times as long as thick as thickas profile. in profile.

REFERENCES

BINGHAM, C. T. 1903-The fauna of BritishIndia, includingCeylon and Burma: Hymenopteravol. II. London. DODD, F. P. 1902-Notes on the Queenslandgreen tree ants. The VictorianNaturalist, XVIII:136-140, 141-142. D6FLEIN, F. 1905-Beobachtungenan den weberameisen.Biologisches Centralblatt, XXV :497-507. FOREL, A. 1894-Abessinischeund andereAfrikanische ameisen. Mitth. Schweiz. Ent. Gesell., IX:64-100. HINGSTON, R. W. G. 1929-Instinctand intelligence.New York. KEUCHENIUS, P. E. 1914-De beteekenisvan tweebekende mieren, in verbandmet het groeneluizenvraagstukvan de koffie.Teysmannia, XXV :711-716. SMITH, F. 1864-Catalogue of hymenopterousinsects collected by Mr. A. R. Wallace in the islandsof Mysol, Ceram,Waigiou, Bouru, and Timor. Jour.Proc. Linn, Soc., VII:6-48. - 1864-Notes on the geographicaldistribution of the aculeate Hymenopteracol- lectedby Mr. A. R. Wallace in the EasternArchipelago. Ibid. VII:109-145. WEBER, N. A. 1943-The ants of the ImatongMountains, Anglo-Egyptian Sudan. Bull. Mus. Comp. Zool. Harvard, 93:263-389. - 1946-Dimorphismin the African Oecophyllaworker and an anomaly.Annals of the EntomologicalSoc. of Amer.,XXXIX:7-10. WHEELER, W. M. 1910-Ants, theirstructure, development, and behavior.Newv York. WITH THE COLLABORATION OF J. BEQUAERT, I. W. BAILEY, F. SANTSCHI, AND W. M. MANN 1922-Ants of the AmericanMuseum Congo Expedition.Bull. Amer. Mus. Nat. Hist., 45:xi+ 1139.

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