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nests of L. muscorum and L. tuberum. The mixed colonies may contain males and females as well as workers of both the host and parasitic species. The males of sublevis are so much like those of Leptothorax that Adlerz failed to distinguish them till he published his final paper (1896). All the females which he found were wingless and ergatoid, with a thorax like that of the worker, but with ocelli and a receptaculum seminis. He naturally took these ergatoids to be the only females of the species, but in addition to these Viehmeyer has discovered winged females in some of the colonies in Saxony. Adlerz's observations seem to show that sublevis secures its auxiliaries by attacking Leptothorar colonies, driving away the adult ants and taking possession of their nests and young. The latter are then reared as auxiliaries, or hosts. It is not impossible, however, that sublevis may recruit the number of its auxiliaries by making occasional sorties like Polyergus, for Adlerz succeeded in finding one nest in which the parasites were living with two species of Leptothorax (acervorum and muscorum). The domestic instincts of sublevis are very much blunted or obsolescent. It rarely or never excavates, and although it is able to feed itself if food is within reach, it does not go in quest of it, but leaves this to its host. A number of sublevis which Adlerz isolated with a number of larvæ and some food managed to live for 135 days, but the larvæ shriveled up or died. It seems probable, therefore, that this ant depends on its slaves for the nurture of its young. When the mixed colony moves to a new nest the sublevis are carried by the Leptothorax; very rarely are the rôles reversed. Sometimes when the sublevis endeavor to leave the nest they are restrained by their slaves in much the same manner as Polyergus. Adlerz observed the males mating with the ergatoid females, but this occurred only between individuals. belonging to different colonies. The larvæ of sublevis are so much like those of their hosts that he could not distinguish them. They are nourished both with regurgitated liquid food and with pieces of insects, a method of larval feeding which was also observed by Viehmeyer. This author believes that sublevis was originally lestobiotic like Solenopsis, that is, that it once robbed and devoured the young of an ant in whose neighborhood it nested without forming a mixed colony. The following are his views on the phylogeny of sublevis and its method of establishing colonies: "The starting point of the development was represented by an ant allied to Leptothorax, with males and females, both winged, and, like many other ants, with a predilection for eating the larvæ and pupæ of allied species. This habit, practiced only occasionally at first, became established and the ants took to nesting near other ants, which at first tolerated these thieves unwillingly (compound

nest). The thief ants then gradually became marauders (mixed colony). With increasing dependence on their auxiliaries, which showed itself in the dwindling of the worker instincts and the disappearance of the mandibular teeth, the difficulty of founding colonies. by means of winged females increased and led to the development of the ergatoid forms. In these the ancient lestobiotic and predatory instincts united with the newly acquired female instincts, so that the ergatoids became incomparably better fitted for founding colonies than the winged forms, which therefore tended to extinction. We must still, however, endeavor to explain why the winged females have never been found in the colonies of northern Europe. This may be accounted for in two ways. We may regard the winged female either as a reversion or as the lingering vestige of a not yet completely eliminated. winged form. The latter alternative seems to be indicated by the remoteness of the locality in which this form occurs from the true

B

FIG. 275. A, Harpagoxenus americanus worker and B, its host, Leptothorax curvispinosus worker. (Original.)

geographical range of the species. The development of this sex would probably be unequally advanced in two regions differing so much in climate and other conditions. But we must wait to see whether this ant does not occur also in other regions, perhaps in northern Germany."

2. Harpagoxenus americanus (Fig. 275, A).-This species, which is smaller and of a darker brown color than sublevis, seems to be extremely rare. To my knowledge it has been taken on only three. occasions. The type specimens, describe by Emery (1893-'94), were found by Pergande at Washington, D. C., in a nest of Leptothorax curvispinosus (Fig. 275, B), but no observations on the relations

of the two species were recorded. Schmitt found a few specimens while sifting vegetable mould for beetles near Beatty, Pa., and I found it during the summer of 1905, in a rich, boggy wood near Bronxville, N. Y. Here there were several fine L. curvispinosus colonies nesting in the hollow twigs of elder bushes, and in three of these colonies there were specimens of H. americanus. One contained only a single worker, another six, and a third eight workers and a queen of the parasitic ant. The latter insect was not ergatoid, but decidedly larger than the workers, with well-developed ocelli and a typical, though small, female thorax, showing distinct traces of having borne wings. All three colonies contained larvæ and pupæ, presumably of the parasitic species, but no Leptothorar queens. When confined in artificial nests the americanus were very inactive and paid no attention to the brood. All the colonies were too small to admit of the supposition that they had been formed by repeated forays on the part of Harpagoxenus. This ant, in fact, has every appearance of having reached a more abject stage of parasitism than its European congener. In the same locality I found a mixed queenless colony of the yellow L. curvispinosus and the black L. longispinosus inhabiting a hollow elder twig. If a deälated queen of H. americanus happened to establish her colony in such a nest as this, we should have a case like Adlerz's sublevis living with both L. acervorum and muscorum, but the inference that this indicated repeated slave-making forays on the part of americanus would be erroneous.

B. The Permanent Social Parasites.-The ants included in this group are all small and nearly all of them belong to monotypic genera. The absence of workers makes it difficult to assign definite positions to these genera in our classifications, which are based very largely on the worker forms.

1. Wheeleriella santschii (Fig. 276).-This is a small, dark-brown species, the female of which measures 4-4.7 mm. in length, the male only 3.5-3.8 mm. It was discovered by Santschi in the cactus fields near Kairouan, Tunis, and lives in the nests of the most abundant of all the North African ants, Monomorium salomonis and its varieties. The female Wheeleriella resembles Strongylognathus testaceus in having the posterior border of the head deeply excised and its posterior corners projecting as blunt horns. Santschi's interesting observations have been published by Forel (1906d) and may be briefly summarized. Although both sexes have well-developed wings, mating seems to take place, at least as a rule, in the outer galleries of the nest and between brothers and sisters (adelphogamy). After fecundation the deälated female roams about over the surface of

the soil in search of Monomorium nests. When near the entrance of one of these, she is "arrested," to use Santschi's expression, by a number of Monomorium workers, which tug at her legs and antennæ and sometimes draw her into the galleries. At other times she may be seen to dart into the nest entrance suddenly, so that she is arrested within the nest itself. There are no signs of anger on the part of the Monomorium and she is soon able to move about in the galleries without restraint. The workers forthwith feed and adopt her. In the course of a few days she begins to lay eggs which are received and cared for by the Monomorium workers. Santschi observed that the colonies infested with Wheeleriella were usually of small size, had an impoverished appearance and lacked queens of the host species, and he was able to account for these peculiar conditions. The Wheel

FIG. 276. Wheeleriella santschii of Tunis; female; (Original.)

eriella queen pays no attention to the much larger Monomorium queen, but this insect is assassinated by her own workers and the parasitic queen is adopted in her place. Forel believes that this singular perversion of instinct is due to the preference of the workers for a smaller fertile individual, just as the Tetramorium workers prefer to rear the small males and females of Strongylognathus instead of their own bulky sexual phases. This explanation is not satisfactory, how

very

ever, for, as we have

seen, the huge mother Tetramorium is retained in the nest, whereas it is precisely this individual that is destroyed in the infested Monomorium colonies. Hence there must be some other reason for the assassination of the host queen by her own progeny.

2. Epixenus andrei and creticus.-These ants have been recently described by Emery (1908a), the former from females taken between Jaffa and Jerusalem in a nest of Monomorium venustum, and originally referred to this species by Ern. André (1881b), the latter from a single

male taken in Crete. As both species are related to Wheeleriella santschii, Emery believes that they lack the worker caste.

3. Sympheidole elecebra (Fig. 277, A).-This species, which is much smaller than Wheeleriella (female 2.75-3 mm.; male 2.5-2.75 mm.), lives in the nests of Pheidole ceres, a common ant in the mountains of Colorado and New Mexico at altitudes between 2,500 and 3,000 m. The parasites and host are very similar, but the female of the former is much smaller, has a more rounded head and a very broad post-petiole. I have seen only two females: one taken by Schmitt in a ceres nest at Boulder, Colo., the other with eighteen males, taken by myself August 17, 1903, in the Ute Pass, near Manitou in the same state. The ceres colony in which I found these ants was carefully examined, but contained only workers and soldiers of the host species, and besides the adult parasites, a number of their pupæ. No workers of the latter species could be detected, though from what we know of other ants, they should have been in the nest, if they exist at all, at the time of maturity of the males. When the nest, which was under a stone, was first disturbed, the Pheidole

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workers seized the parasites and their pupæ and quickly carried them into the galleries. As there are usually from one to five deälated queens in the uninfested colonies of ceres, their absence in this nest shows that they must have been eliminated. And as the elecebra queens are very small and feeble compared with the ceres queens (which measure 5-5.5 mm.), it is probable that the latter are killed by their own workers and soldiers.

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4. Epipheidole inquilina (Fig. 277, B).-Like the Sympheidole, this ant resembles its host, which is also a common Pheidole (P. pilifera). Emery (1893-'04) saw the small queen of Epipheidole (length 3-3.3 mm.) among some soldiers and workers of pilifera collected in Nebraska, but he regarded the insect as an unusually microgynic Pheidole. During late July and early August, 1903, I found near Colorado Springs three colonies of Ph. coloradensis, a subspecies of

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