Janet calls attention to two other Gamasids, Uropoda ovalis (Fig. 247, A) and Urodiscella philoctena (Fig. 247, B). The former attaches itself by means of a glue-like secretion to the legs of ants, the latter clings to the comb of the strigil by means of one of its fore legs. This species evidently feeds on the dirt which is scraped by the ant from its body and appendages. A similar mite is sometimes found attached to the spurs on the legs of our American carpenter ant (Camponotus pennsylvanicus). Still another Gamasid, Oölelaps oöphilus, has been described by Wasmann. It is found on the eggs and packets of very young larvæ of Formica sanguinea and rufibarbis and lives on the salivary secretion with which the ants coat their young progeny. Many of the mites found attached to adult ants probably feed on the same substance.

Wasmann (1897e) has also published some observations on a Sarcoptid mite (Tyroglyphus wasmanni) which lives in the nests of F. sanguinea and, in the adult, nymphal and larval forms, feeds on dead ants. At times, however, its hypopi become exceedingly numerous and cover the bodies of the living ants in masses. These hypopi always orient themselves with their heads towards the distal end of the appendage or part of the body on which they are resting. They seem to take no nourishment, but their great numbers impede the ants' movements and eventually kill them.

Some of the beetles of the family Thorictidæ, comprising the single genus Thorictus of the Mediterranean region, must also be included among the ectoparasites, if we accept Wasmann's account of their habits (1898a, 1898b). These are small, subtriangular, reddish brown creatures, with tufts of golden trichomes at the posterolateral corners of the prothorax. Several of the species, like the myrmecophilous Histeridæ, seem to live on dead ants, but others (T. foreli and pauciseta) are regularly found, as Forel (1894a) first observed, attached by means of their bidentate mandibles to the antennal scapes of Myrmecocystus workers. The host of T. foreli is M. megalocola, that of pauciseta, M. desertorum. The prothorax of the beetle is provided with a groove or depression to fit the scape, towards the distal end of which the beetle's head is always directed (Fig. 248). In this position the insect may remain for weeks in spite of all the efforts of the ant to dislodge it. Escherich (1898c) found that the beetle is frequently licked and that it sometimes attaches itself to the legs as well as to the antennæ. Wasmann maintains that it punctures the scape and sucks the blood of the ant and that Thorictus is therefore both an ectoparasite and a symphile. Other species of the genus seem not to have this habit of clinging to the ants. Mr. Walter Granger

brought me from the Fayum several specimens of Thorictus castaneus which he found free in the chambers of a Myrmecocystus bombycinus nest. These have much larger trichomes than either foreli or pauciseta and lack the peculiar prothoracic depression.

It has been found that certain groups of Chalcidid Hymenoptera, notably the Eucharinæ, contain a number of very interesting antparasites, which are often brilliantly metallic and have bizarre forms. The first of these (Eucharis myrmecia) was discovered in the cocoon. of a bull-dog ant (Myrmecia forficata) by Forel (1890a), who believed it to be an entoparasite. Cameron (1891) described another species (Chalcura bedeli) from the nests of the Algerian Myrmecocystus viaticus, and more recently (1907a) I have shown that species of several other Eucharine genera (Orasema, Pseudochalcura, Kapala, Isomeralia, Pseudometagia) are ant-parasites (Figs. 249 and 250). The life history of only one of the species, Orasema viridis, is at all adequately known (Fig. 251). This is a brilliant metallic blue and green fly which lives in the nests of several Texan and Mexican Pheidole, especially Ph. instabilis. The young larva is somewhat thysanuriform and attaches itself to the neck of the ant-larva, sucking out its juices and in the course of a few days undergoing several ecdyses, pupating and hatching, without necessarily withdrawing sufficient substance from the ant-larva to prevent its pupating in turn. But such larvæ have nevertheless lost much of the material which in uninfested individuals goes to form the head, thorax and eyes of the adult, so that these parts are very poorly developed in the pupæ. These pupæ, which I have called phthisergates (Fig. 252, B and C), phthisogynes and phthisaners, according as they arise from depleted worker, female or male larvæ, never hatch. Both the larval and adult Orasema are effusively licked and fondled, and the latter are even fed by the Pheidole workers. The Chalcidids, however, have no affection for the ants, but endeavor to leave the nest at the earliest possible moment in order to mate in the open fields. Another Orasema (O. coloradensis) leads a similar life in the nests of Solenopsis validiuscula and Ph. vinelandica in Colorado, and a third species (O. wheeleri) was found in the nests. of Ph. ceres in western Texas. I have also found the pupæ of Pseudochalcura gibbosa in the cocoons of Camponotus noveboracensis, together with remains of the ant-pupæ, showing that the eggs and young larval Chalcidids must attach themselves to mature Camponotus larvæ ready and able to spin their cocoons. Two to four of the Pseudochalcura pupæ sometimes occur in a single cocoon. For further details concerning the parasitic Chalcidids, the Lomechusini and several

other myrmecophiles the reader is referred to my paper on the "Polymorphism of Ants" (1907a).

The Entoparasites.-These constitute an even more diversified assemblage of forms than the ectoparasites. The only entoparasitic Coleopteron, however, is the Stylopid Myrmecolax nietneri, described by Westwood (1861) from the gaster of a Ceylonese ant. The habits of this beetle probably resemble those of the species of Stylops and Xenos which develop in the abdomens of bees and wasps. Among the remaining entoparasites may be mentioned certain Diptera, Hymenoptera and Nemathelminthes.

The Diptera are represented by several Phorida and the Conopid genus Stylogaster. The Phorid Apocephalus pergandei, according to Fox (1887) and Pergande (1900), lays its eggs on the heads of Camponotus pennsylvanicus workers. The larvæ hatching from these eggs enter the cranial capsule through the occipital foramen and feed on the tissues, causing the ant to become very lethargic. Later the creature literally loses its head, and the larvæ pupate and hatch. Pergande has described the frantic efforts of the ants to rid themselves of these terrible executioners. Coquillet (1907) has recently described another Phorid, Plastophora crawfordi, which was taken in the act of ovipositing on the head of a Solenopsis geminata in Texas. I have already alluded to the various peculiar Phorids with wingless females (p. 383). They, too, may be entoparasitic in their larval stages, but as there is no evidence of such habits, I have placed them among the synceketes.

As the Conopidæ are known to be parasitic in the bodies of adult bees and wasps, it is not surprising to find that some of these flies also attack ants. Bates (1893) observed species of the genus Stylogaster hovering over Eciton armies in Brazil, and Townsend (1897) captured numbers of three species of the same genus in Mexico, while they were following an army of Eciton foreli. There can be little doubt that they lay their eggs on the bodies of the ants and that the larvæ are entoparasitic.

Among the entoparasites is also to be included a number of minute Hymenoptera of the families Braconidæ, Chalcidida and Proctotrupida. The best known of these is the Braconid Elasmosoma berolinense, which has been seen by Giraud (1871), Forel (1874), Pierre (1893), Olivier (1893), and Wasmann (18949) ovipositing on the

bodies of Formica, Camponotus and Lasius. The larva of the parasite develops in the ant's gaster. Wasmann (1899) has described and figured two interesting European Proctotrupids, Solenopsia imitatrix, from the nests of Solenopsis fugax, and Tetramopria aurocincta, from those of Tetramorium cespitum. Solenopsia seems to mimic the Solenopsis workers and Tetramopria is provided with golden trichomes and for this reason is regarded by Wasmann as a true guest. Ashmead (1893) enumerates among American Bethylids four species of Pseudisobrachium (mandibulare, montanum, myrmecophilum and rufiventre) as living in the nests of Formica and Camponotus. An exquisite, subapterous, purple, green and gold Asaphine Chalcidid, Pheidoloxenus wheeleri (Fig. 253), which lives in the nests of Pheidole instabilis, is probably also entoparasitic on the ants or their progeny during its larval stages.

Finally, we come to a number of extraordinary round worms which live in ants or their larvæ. Janet (1893e, 1897e) and de Man (1894) have described several Nematodes from the bodies of worker ants. The former investigator saw some of these worms, several centimeters long, issue from the orifice of the labial glands of Formica fusca, and he and de Man described another form, Pelodera janeti, which lives in the pharyngeal glands of Lasius and Formica. "Within these glands the Pelodera are bathed in a yellow liquid on which they feed. They complete a larval stage in the glands and then escape from them to live a free life on the detritus of the nest. There they give rise to a series of generations whose larvæ are distinctly different from those living in the heads of the ants and develop without entering the insects." Other Nematodes belonging to the family Anguillulidæ have been seen. in ants' nests, but nothing is known concerning their habits and development. The Gordiids are represented by Gordius formicarum, which von Siebold took from the gaster of an ant, and by Mermis, the larvæ of which live in the crops of the larval, pupal and adult workers of several different neotropical Formicidæ and produce a great distension of the gaster in the imaginal instar. I first observed these parasites in the Texan Pheidole commutata (1901d, 1907a). They enter the larva and apparently by unduly stimulating its appetite cause it to be fed excessively, so that it becomes unusually large at the time of pupation and produces a gigantic worker form, with ocelli (Fig. 254, B and C). This form, which I have called the mermithergate, was first seen by Emery (1890d) in the Costa Rican Pheidole absurda, but he supposed Cockerell ("A New Braconid of the Genus Elasmosoma," Proc. Ent. Soc. Washington, 10, 1908, pp. 168, 169) has recently described a species of Elasmosoma (E. vigilans) parasitic on Formica subpolita in Colorado.

1

it to be an egg-laying " parthenogenetic female." Since the publication of my paper (1901d) he has reëxamined this specimen and several other worker ants with larger gasters and traces of ocelli in his collection and has found them to contain Mermis. Besides the two species already mentioned, he has recorded the occurrence of mermithergates in Odontomachus hæmatodes and chelifer, Neoponera inversa, Ectatomma tuberculatum, Pachycondyla fuscoatra and Paraponera clavata. These pathological forms therefore occur rather generally, at least in the neotropical Myrmicinæ and Ponerinæ.

It is interesting to compare the modifications induced in their respective hosts by the parasites Orasema, Mermis and Lomechusa.

B

Parasitism of Mermis in Pheidole commutata.

(Original.)

A, Nor

FIG. 254. mal worker of Pheidole commutata; B, mermithergate, or worker containing Mermis parasite which it possessed as a larva; C, same, lateral view.

While the effects in all three cases are wrought through a withdrawal of nourishment from the developing larvæ, each of the parasites adopts a different method. Thus the ectoparasitic Orasema larva extracts important juices from the body of the Pheidole larva directly and with great rapidity, thereby reducing its host to a mere skin, which, though still able to pass on to the pupal stage, no longer possesses sufficient substance or vitality to reach the imaginal stage. The Mermis larva