G. C. Wheeler and J. Wheeler.
The Ant Larvae of the Nyrmicine Tribe Myrmicini.
Psyche 59:105-125, 1952.

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THE ANT LARVAE OF THE MYRMICINE TRIBE
MYRMICINI1
BY GEORGE C. WHEELER AND JEANETTE WHEELER Department of Biology, University of North Dakota The tribe Myrmicini comprises four genera: the New World Pogonomyrmex, with some three dozen species; the rare Ethiopian Cratomyrmex (which may not even belong in this tribe), with only two species; the common Holarctic (and also Indomalayan) Myrmica, with about 30 species ; and the Holarctic Manica with half a dozen species. This tribe is interesting partly because it includes har- vesters (Pogonomyrmex and Cratomyrmex) , but chiefly be- cause it is the most primitive tribe of the subfamily Myrmicinae. (Wheeler, Bull. Mus. Nat. Hist. 45:660. 1922). Wheeler (ibid., p. 24) regarded Hylomyrma as the most primitive genus in the tribe, with Pogonomyrmex next. Emery (Genera Insectorum, 1921-22), however, placed the Metaponini first, the Pseudomyrmini second and the Myrmicini third; within the Myrmicini he put Myrmica first, Cratomyrmex second and Pogonomyrmex third; Hylomy~ma is treated as a subgenus of Pogono- m e x . Our studies on the larvae support Wheeler's arrangement of Pogonomyrmex and Myrmica. Pogono- myrmex larvae are certainly more primitive than Myrmica larvae, as is evidenced by the following characters: the lack of anchor-tipped hairs on the abdomen; spinules on the posterior surface of the labrum coarse and isolated; mandibles stouter, with two large coarse mesal teeth and without mesal blade or concavtiy.
In this article we have described the larvae of three species of Pogonomyrmex and eight species of Myrmica. References from the literature are cited for one other genus and five additional species making a total of three genera and sixteen species considered.
IThe research on which this article is based was aided by a grant- in-aid from the Sigma Xi Research Fund.




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106 Psyche [September
Tribe MYRMICINI (F. Smith)
Stout; diameter greatest at the fourth or fifth abdominal somite ; slightly attenuated anteriorly ; thorax very stout (when mature) and arched or bent ventrally, but not dif- ferentiated into a neck; posterior end broadly rounded. Antennae each with three (rarely two or four) sensilla, each of which bears a stout spinule. Head hairs short to long; mostly denticulate. Labrum small and short; breadth twice the length; bilobed; anterior surface of each lobe with 2-5 minute hairs and 1-5 sensilla; posterior surface spinulose and with 8-18 sensilla. Mandibles rather small or moderate-sized (ratio of head width to mandible length 2.1-2.9, average 2.5) ; stout (ratio of length to width at base 1.8-2.4, average 2.1) ; heavily sclerotized; no spinules. Apex of maxilla usually spinulose; palp and galea paxilli- form, bearing respectively five and two sensilla ; palp slight- ly shorter than or equal to galea. Anterior surface of labium usually spinulose ; palp a low elevation bearing four or five sensilla; opening of sericteries a short transverse slit (concealed in a groove). Hypopharynx usually sparsely spinulose, the spinules minute and generally in transverse rows.
Genus Pogonomyrmex Mayr
Stout; diameter greatest at the fourth or fifth abdominal somite ; slightly attenuated anteriorly ; thorax very stout (when mature) and arched or bent ventrally, but not dif- ferentiated into a neck; posterior end broadly rounded; anus terminal or subterminal. Body hairs moderately numerous ; mostly denticulate ; anchor-tipped hairs lacking. Antennae each with three sensilla, each of which bears a stout spinule. Head hairs short to long; sparsely denticulate on the distal half. Labrum small and short; breadth twice the length; bilobed; anterior surface of each lobe with two or three minute hairs and 3-5 sensilla; ventral border of each lobe spinulose and bearing two contiguous sensilla; posterior surface with a few coarse spinules and numerous sensilla. Mandibles with the apex forming a rather long and moderately slender tooth which is round-pointed and which tapers slightly.
Wheeler & Bailey, 1920, p. 251: "Certain agricultural



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19521 Wheeler and Wheeler - Ant Larvae 107 ants, which feed on seeds (Pogonomymnex, Messor) also nourish their young with the same food." Wheeler (1928, p. 202) stated that the larvae of this genus are fed with fragments of seeds, but the very young- est larvae are fed on regurgitated food. (=1926, p. 243.)
Pogonomyrmex barbatus (5'. Smith)
(PI. 11, figs. 14-22)
Stout; diameter greatest at the fifth abdominal somite, slightly attenuated anteriorly ; thorax very stout and arched ventrally but not differentiated into a neck; posterior end broadly rounded. Anus subterminal. Leg, wing and gono- pod vestiges present. Nine differentiated somites. In- tegument sparsely spinulose on the ventral surface of mesothorax, metathorax and anterior abdominal somites and on the dorsal surface of the last few abdominal somites. Body hairs moderately numerous and rather uniformly distributed; with the distal half finely denticulate. Of two types : (1) short (0.05-0.12 mm) , uniformly distributed ; (2) long (0.31-0.42 mm), moderately abundant on the ventral surface of the thorax, elsewhere reduced to a single row around the middle of each somite. Cranium subcircular in anterior view, but with the genal outlines somewhat flattened.
Antennae small slightly raised discs
each with three sensilla, each of which bears a moderately long sharp spinule. Head hairs numerous, short to long (0.045-0.14 mm), with the distal half sparsely denticulate. Labrum small and short (breadth 2X length), bilobed, not narrowed ventrally; anterior surface of each lobe with two minute hairs, five isolated sensilla and a few minute spinules; ventral border of each lobe with two sets of two contiguous sensilla and a few spinules; posterior surface of each lobe with two contiguous and about five scattered sensilla, sparsely spinulose, the spinules coarse and iso- lated or in short rows. Mandibles robust and heavily sclerotized; apical tooth moderately long, moderately slender, tapering only slightly to a round point; medial teeth short, robust and round-pointed, the proximal curved medially and posteriorly, the distal pointed anteroventrally. Maxillae with the apex conoidal and spinulose, the spinules minute and isolated or in short rows; palp paxilliform with



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108 Psyche [September
four apical and one lateral sensilla; galea paxilliform with two apical sensilla. Labium with the anterior surface spinulose, the spinules minute and isolated or in short trans- verse rows; palp a short protuberance with five apical sen- silla; opening of sericteries a short transverse slit (con- cealed in a groove). Hypopharynx sparsely spinulose, the spinules minute and in short subtransverse rows. ( Material studied: numerous larvae from Texas.)
Forel, 1921, Fig. 1B on p. 23 ; larva in side view (after Wheeler). (=1928, Vol. I, Fig. IB.)
Wheeler, 1900: "Still another modification of the 'polls d'accrochages' is seen in Pogonomyrmex barbatus, the young larvae of which have the longer bristles serrate on the apical half, so that they remind one of the hairs of cer- tain mammals9'
( p. 21) . Fig. 9a, nearly mature larva ; b, young larva ; c, hair of latter (p. 20). Wheeler, 1910 : Fig. 42 on p. 76 repeats 1900, fig. 9; Fig. 36 on p. 70, photograph of five larvae. "The larvae, as in E. imberbicuhs, are fed with pieces of crushed or broken seeds. In my artificial nests these pieces were coated with saliva by the workers before being administered to the brood, a precaution which may insure the conversion of starch into sugar and facilitate its assimilation by the larvae" (pp. 290-293 ) .
Wildermuth and Davis, 1931: The larvae are "cream Pogonomyrmex occidentalis (Cresson), Figs. 1-13,-1, head in an- terior view, X44; 2, labrum (left half of drawing shows posterior view, right half, anterior view) Xl18; 3, labium in anterior view, X118; 4, right labial palp in anterior view, X340; 5, left mandible in anterior view, X118;
6,
left mandible in medial view, X118; 7, left antenna in anterior view, X340; 8 and 9, two long denticulate body hairs, X95; 10, mature larva in side view, X10;
11, simple body hair, X96; 12, short
denticulate body hair, X96; 13, submature larva, X10. Pogonmyrmex barbatus (I?. Smith), Figs, 14-22. - 14, head in an- terior view, X44; 15, labrum (left half of drawing shows posterior view, right half, anterior view) X118; 16, left mandible in anterior view, X118; 17, left mandible in medial view, X118; 18, right antenna in lateral view, X340; 19, right antenna in anterior view, X340; 20, mature larva in side view, X10; 21, submature larva in side view (hairs omit- ted), X10; 22, two body hairs, X95.




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110 Psyche [September
colored and are shaped like crooknecked squashes, the smaller crooked portion ending in a very small head. The length of the full-grown larva, not including the portion turned back is about one-fourth of an inch" (p. 3). Fig.
ID, larva in side view.
Pogonomyrmex occidentalis (Cresson)
(PI. 11, figs. 1-13)
Stout; diameter nearly uniform throughout but with the thorax somewhat attenuated and bent ventrally; no neck; posterior end broadly rounded. Anus terminal. Leg, wing and gonopod vestiges present. Nine differentiated somites. Body hairs moderately numerous, uniformly distributed. Of three types: (1) short (0.036-0.08 mm), with the distal half finely denticulate and the base stout to slender, uni- formly distributed; (2) long (about 0.27 mm) hairs with the distal half finely denticulate; a few in a single row around the middle of each sornite and also on the venter of the prothorax and of the last abdominal somite; (3) smooth and long (0.18-0.35 mm), with slender base and long flexible tip, restricted to the ventral surface. Cranium transversely subelliptical, somewhat broader than long. Antennae small slightly raised discs, each with three sen- silla, each of which bears a short stout spinule. Head hairs moderately numerous, short, to lfong (0.045-0.11 mm) , sparsely denticulate on the distal half. Labrum small and short (breadth 2X length), bilobed, somewhat narrowed ventrally; anterior surface of each lobe with three minute hairs, an isolated sensillurn near the middle and a pair of contiguous sensilla near the ventral border; ventral border of each lobe with spinules and a pair of contiguous sensilla; posterior surface of each lobe with three or four isollated and one or two sets of two or three sensilla each and a few coarse and mostly isolated spinules. Mandibles robust, heavily sclerotized ; apical tooth long, tapering only slightly to a rounded point; the two medial teeth are shorter but still quite long, subequal and round-pointed. Maxillae with the apex paraboloidal and spinulose, the spinules coarse and isolated; palp paxilliform with two apical, two sub- apical and one lateral sensilla; galea paxilliform, shorter than palp, with two apical sensilla. Labium with the



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19521 Wheeler and Wheeler - Ant Larvae Ill anterior surface moderately spinulose, the spinules minute and isolated or in short transverse rows; palp a stout sub- cone bearing three apical and one lateral sensiila; opening of sericteries a short transverse slit (concealed in a groove). SUBMATURE: Shaped somewhat like a crookneck aquaah, the thorax forming a moderately slender neck which is strongly arched ventrally, the abdomen elongate, sub- ellipsoidal and moderately stout; posterior end narrowly rounded. Anus subterminal. Otherwise as in the mature larva.
(Material studied: numerous larvae from North Da- kota,)
Pogonomyrmex (Ephebomyrmex) imberbicvlus Wheeler Wheeler, 3902, p. 90 : House flies were "cut into pieces and fed to the larvae in the same manner as I have des- cribed for the Fonerinae and some Myrmicinae. On one occasion nearly every larva in the nest could be seen munch- ing a small piece of house fiy. But a still more remarkable method of feeding was adopted after a few days, when the supply of insect food was exhausted. Then the ants were seen to bring seeds from their granary, crack them open with their strong mandibles, and, after consuming some of the softer portions themselves, to distribute the remainder among their larvae. The latter could be seen under the lens cutting away with their mandibles and devouring- the softer starchy portions of the seeds . . These observations show that the larvae of certa'in ants are not only oble to subsist on solid food, but even on food of a, vegetub Ie nature. The adaption of what were probably once exclusively carni- vorous ants to a vegetable diet, although not yet complete, is, nevertheless, so far advanced that the larva already participates in the peculiar feeding habits of the adult in- sect. The P. imberbicutw seem not to possess the power of feeding one another or their larvae by regurgitation. At any rate they were not seen to make use of this method in the artificial nests." (Brief mention by Wheeler, 1910, p. 284 and 1933, p. 15 and by Wheeler and Bailey, 1920, p. 251.)
Pogonomyrmex (Ephebomymex) naegelii Fore1 Eidmann, 1936, p. 39: "Die spiirlich beborsteten Larven



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112 Psyche
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zeigen ebenso wie die nackten Puppen keine bemerken- swerten Besonderheiten."
Pogonomyrmex (Forelornyrmex) mayri Fore1 Apparently similar to occidentalis except for the follow- ing characters: Head oval in anterior view, somewhat longer than broad. Head hairs few. Anterior surface of each lobe of labrum with two minute hairs and four sen- silla; posterior surface with five scattered sensilla on each lobe. Mandibles larger and more elongate, the medial teeth more blade-like. Labial palp with four apical and one lateral sensilla. (Material studied: three integuments (without hairs) from Colombia.)
Genus Myrmica (Latreille)
Stout; diameter greatest at the fifth abdominal sornite; slightly attenuated anteriorly ; thorax very stout and arched ventrally, but not differentiated into a neck; posterior end broadly rounded ; anus posteroventral. Body hairs sparse ; minute to long, of three types - (1)
simple, (2) denticul-
ate and (3) anchor-tipped ; anchor-tipped hairs in trans- verse rows of 2-4, restricted to the dorsal surface of the 5-8 anterior abdominal somites, one row on each somite. Antennae each with three (rarely two or four) sensilla, each bearing a stout spinule. Head hairs few, short to long, mostly denticulate. Labrum small and short, breadth twice the length; bilobed; anterior surface of each lobe with 2-4 minute hairs and usually one or two sensilla; ventral border of each lobe with two sets of two contiguous sensilla each; posterior surface with minute spinules ar- ranged in rows and with 8-18 sensilla. Mandibles with the apical third stout, sharp-pointed and slightly curved medial- ly; anterior surface produced mesally into a thin blade, which usually bears one small stout tooth and which may be denticulate near the base; mesa1 surface concave. Adlerz, 1886 : "Some larvae with hairs shorter and simple or moderately branched at the tip, some with longer hairs which are either provided with short lateral spines or are shortly branched at the tip. The tips of the uncinate hairs vary but the anchor-like shape is the most common" (p. 259; translated from Swedish by Professor Edith E.



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19521 Wheeler and Wheeler - Ant Larvae 113 Larson). Transitional types occur (p. 258). PI. 7, fig. 6, four hair tips. Internal anatomy, p. 58. Donisthorpe, 1915, p. 109: "Yellow, narrow anteriorly, broad posteriorly; the segments gradually increasing in width until quite close to the base. The whole body covered with hairs, which are much more abundant in the young larvae. The first to the sixth abdominal segments are furnished on the dorsum with a pair of long anchor-tipped hairs, which are generally absent in the full-grown larvae. Some of the other long hairs possess a single hook instead of an anchor-tip, some hairs are serrate, and some bifurcate or trifurcate."
(Repeated 1927a, p. 117.) Fig. 44 on p. 32 in both editions: Two hairs "on Myrmica larva". Donisthorpe, 19275: Staphylinid beetles of the genus Atemeles prey upon the larvae of Myrmiea (p. 17). Staphy- linid beetles of the genus Lamprinus and their larvae de- vour Myrmica larvae (p. 72).
Janet, 1904, pp. 31-32: "Quant aux petites larves, elles s'accrochent les unes aux autres par des poils speciaux. Chez la Myrmica, et chez bon nombre d'autres Myrmicidae, cet accrochage se fait par de longs poils termin& par des crochets simples ou double. Ces poils sont disposes r6gu- lierement en petit nombre sur chaque anneau. Les nouveaux poils, form& A la suite d'une mue, ne sont pas exactement semblable A ceux de la cuticule exuvi6e." Starcke, 1948, pp. 26 and 28: "The ordinary hookform with the head bent perpendicularly to the body or even a little further, the thoracal segments ranged fan-like, the abdomen next without any special demarcation, straight, and only the extremity a little swollen, with some whitish spots of urate cells shining through.
Usually the head is
for one third sunk into the prothorax. With the fullgrown larva, the head grows still more into the prothoracical seg- ment, until more than half its volume is situated there . . . There are 13 postcephalic segments of which the last 3 or 4 are not clearly marked. Newly emerged larvae are portly and ho'oklike from the start . . . The head, of a 3 mm larva is 0.42 mm long and at the rear end 0.36 mm broad, the mouth parts are 0.24 mm broad. The most protruding part is the distal sensilla-turret of the maxilla, but the labrum and mandibula do not stay back very far."



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Mywnica emeryana Fore1
(Text fig. 1, figs. 1-3 and 6-15)
Stout; diameter greatest at the fifth abdominal somite, slightly attenuated anteriorly ; thorax very stout and arched ventrally but not differentiated into a neck; posterior end broadly rounded. Anus posteroventral. Leg, wing and gonopod vestiges present. Eleven differentiated somites. Integument spinulose on the dorsal surface of the posterior somites and on the ventral surface of the mesothorax, metathorax and first few abdominal somites; the spinules sparse and minute, isolated or in short transverse rows. Text figure 1. Myrmica emeryana Forel, Figs. 1-3 and 6-15. -1, head in anterior view, X67; 2, left mandible in anterior view, X185; 3, left mandible in medial view, X185; 6, very young larva in side view (hairs omitted), X20; 7, mature larva in side view, X20; 8-10, four long denticulate body hairs, X121; 11, an atypical body hair, X121; 12, anchor- tipped body hair, X121; 13, two simple body hairs, X121; 14, two small denticulate body hairs, X121; 15, and atypical denticulate body hair, X121.
Myrmica monticola Wheeler, Figs. 4-5. - 4, left maxillary palp in lateral view, X340; 5, right antenna in lateral view, X340.



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19521 Wheeler and Wheeler - Ant Larvae 115 Body hairs sparse, somewhat sparser on the ventral surface of the abdomen, minute to long. Of three types : (1) simple, minute to short (0.003-0.054 mm) , generally distributed ; (2) denticulate, minute to long (0.012-0.28 mm) , the most abundant type, (3) anchor-tipped, long (about 0.28 mm), with the shaft flexuous, four in a row across the dorsal surface of each abdominal somite I-VIII. The denticulate hairs are extremely variable, the dentilcles may be few to numerous, limited to the tip or extending halfway to the base, closely applied to the shaft or suberect, the tip may be nearly straight, strongly curled or bifid. Only simple hairs are found on the ventral surface. Cranium as broad as long, broadest at the dorsal corners which bulge laterally, occipital outline rounded. Antennae with three (rarely four) spinulose sensilla each. Head hairs few, short to long, longest near the occipital border. Of two types: (1) denticulate, 0.05-0.21 mm ; (2) simple, 0.035-0.07 mm. Labrum small, short (breadth 2X the length), bilobed, somewhat narrowed ventrally ; anterior surface of each lobe with three or four minute hairs and a sensillum; ventral border with two sets of two contiguous sensilla each; posterior surface of each lobe with a central spinulose area, the spinules minute and in short transverse rows; six or seven scattered sensilla on the posterior surface of each lobe. Mandibles rather small and heavily sclero- tized; distal third forming a stout, sharp-pointed apical tooth which is curved medially and which has a concavity on its mesa1 surface; anterior surface produced medially into a narrow blade, the edge of the blade variable but usually with one small, stout tooth near the base of the apical tooth and with a few denticles on the proximal half. Maxillae with the apex paraboloidal; palp a skewed peg with two apical, two subapical and one lateral sensilla; galea a frustum with two apical sensilla. Labial palp a low rounded elevation with five sensilla; opening of seric- teries a short transverse slit (concealed in a groove). Hypo- pharynx with a very few rows of minute spinules. (Material studied : numerous larvae from Massachusetts, Michigan and North Dakota.)
YOUNG: Length 2 mm. Similar to the mature larva except in the following details: Body curved ventrally. Anchor-



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116 Psyche
[September
tipped hairs may occur on the mesothorax and metathorax (2-4 on each) and the long denticulate hairs on the lateral surfaces of the mature larvae may be replaced by anchor- tipped hairs to a total of eight per somite. No spinules on
the ventral surface.
Myrmica americana W eber
Similar to emeryana except in the following details: Hairs about twice as numerous on the thorax and four times as numerous on the abdomen. Anchor-tipped hairs usually reduced to two per somite and restricted to ab- dominal somites I-V, even some of these may be replaced by hairs with bifid denticulate tips. Posterior surface of labrum more generally spinulose ; posterior surface of each lobe with five isolated and a cluster of two to four agglomer- ated sensilla.
Mandibles with the apical tooth more slender and the mesa1 border serrate. Labium with anterior surface sparsely spinulose, the spinules minute and in short trans- verse rows. Hypopharynx sparsely spinulose, the spinules minute and in widely spaced transverse rows. (Material studied : numerous larvae from North Dakota.) Tanquary, 1913, PI. LXIV, fig. 36: an embryo just before hatching. The ant was called M. sabdeti. Myrmica brevinodis Emery