Orlando Park.
Ecological Observations upon the Myrmecocoles of Formica ulkei Emery, Especially Leptinus testaceus Mueller.
Psyche 36:195-214, 1929.

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19291 Myrmecoco1e.s of Formica zdkei
ECOLOGICAL OBSERVATIONS UPON THE MYRME-
COCOLES OF' FORMICA ULKEI EMERY, ES-
PECIALLY LEPTINUS TESTACE US
MUELLERI
Whitman Laboratory, University of Chicago In the autumn of 1928 certain observations were made upon the blind beetle, Leptinus testaceus Mull. in the Chi- cago area ,which was found associated with other species of Coleoptera in the nests of the mound-building ant, Formica ulkei Emery. Some of these data are presented at this time. The Ecological Status of Leptims testaceus. Leng (1920) gives the general distribution of this species as Europe, Iowa, Ohio, Pennsylvania, District of Columbia, and British Columbia, and Brendel (1887) lists testaceas from the vicinity of Peoria? Illinois. Its presence in the Chi- cago area is attested to by only two previous records, e-g., Longley (1905) found a solitary specimen in a mouse nest at Clarke, Indiana, and Blatchley (1910) records the species from Lake County, Indiana, finding it from March 11 to December 1, when it probably hibernates in the imaginal state.
This leptinid apparently has a wide range of hosts, being found upon, or in the nest of, wood-mice? field-mice, moles, 1The term "Myrmecocoles" is used here, rather than "Myrme- cophiles", not as an additional burden to the terminology. The usage of the former is broader, embracing all of those species occurring in the nests of ants, and less definite, since the degree of association between occupant and host is not known with exactness in many instances, and consequently reserves for the latter term species where an inbimate relationship is known to exist.



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196 Psyche [September
shrews, rats and small mammals in general, especially the rodents and insectivores (LeConte, after Brendel, 1866 ; Riley, 1889; Schwarz, 1890; Dury, 1892; Kellogg, 1914, and Jeannel, 1922) ; in the nests of birds (Imms, 1924) ; in the nests of Hymenoptera, viz. Vespidae, Bombus, and Formica (Jeannel, l.c., and Imms, 1.c.) . Irnms (1.c.) has even mentioned its occurrence in rotton wood, and it was taken under "chalk flints" by Hardy (1848). The exact relation of this species.to its several hosts is not definitely known. Its status has been variously placed as that of an ectoparasite feeding upon the hair or secre- tions of small host mammals; as that of a scavanger, living on the nest refuse; as a tolerated guest; or as one of those species exhibiting phoresy, and the literature is partially covered and the questions involved discussed by Kellogg, 1914, Riischkamp, 1914, and Jeannel, 1922. Dury and Blatchley believe this leptinid to be a guest, possibly even feeding upon mites and fleas associated with testaceus in mammal nests. The presence of the species in decaying wood may indicate ability to live a more active life, or may be an accidental occurrence. On the other hand, testaceus may exhibit phoresy. This uncommon phenomenon has been discussed by a number of investigators, among which may be mentioned the account of Lesne in 1896, Ruschkamp, I.c., Banks, 1911, and Wheeler, 1919.
If testaceus exhibits phoresy, the species may live in the nests of bees, feeding upon honey and pollen, and using small mammals, such as field-mice, for transportation from one nest of bees to another. Testaceus is well-known as an inhabitant of the nests of bumble-bees, e.g., the work of Gorham in 1869; and Wheeler, 1923, p. 113, says of these bees that their colonies are an annual occurrence. The fecundated queen overwinters and in the spring chooses a small cavity in the ground or in a log, p~eferably the aban- doned nest of a mouse, to line with grass or other materials at hand and so start the incipient colony. It is an interesting possibility that testaceus may live as a guest in the nests of Hymenoptera, and exhibit phoresy as the occasion arises. It is even possible that this phoresy, if it exists, is a stage in parasitism and the blind condition of the beetles would



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10291 M~rrnecocoles of Formica dkei 197
strengthen this view, especially since it has a relative (Leptinillus validus) with greatly reduced eyes. Another related species (Leptinillus aplodontiae) is said to leave its rodent host when the latter is killed, and as soon as the body begins to cool (Ferris, 1918), which may indicate some degree of parasitic adjustment. All of these leptinids have been shown to be closely related to the beaver parasites, Platypsyllidae, (Horn. 1882; Riley, 1889). However, they are also allied rather closely to the Silphidae morphologic- ally (LeConte and Horn, 1883; Sharp and Muir, 1912; Imms, loc. cit.), a family which numbers scavengers, as well as saprovores and carnivores.
The various views that have been held are not necessarily mutually exclusive, and it is possible that the Leptinidae exhibit a facultative parasitism which would explain many of the differing accounts in the literature, and bring into agree.ment the finding of testaceus in habitats suggesting phoresy, a guest relationship, an actual ectoparasitism, a scavenger existence, or a chance occurrence. Leptinus testaceus and other Coleoptera in nests of Formica ulkei.
On October 6, 1928, a trip was made to Palos Park, Illi- llois in search of Pselaphidae. Palos is some thirty miles south-west of Chicago in the glaciated section of the Chi- cago area and is characterized by an oak, elm, hickory sub- climax forest in the upland forest sere of this area (Park, 1929 a, b). A portion of the Palos sector is inhabited by the mound-building ant, Formica dkei Emery. The ulkei
community is rather extensive, especially in the more open clearings of the forest and along the forest margins. The ant has been little studied in nature (Wheeler, 1926). Bur- rill and Smith (1918) record the species from Cedarsburg, Wisconsin, and in a later paper (1919) mention the finding of a larva of the chrysomelid, Coscinoptera dorninicana (Fab.) in an ulkei nest. Recently, Holmquist (1926, 1928 a, b) has given the most complete acco~mt of this ant in the Chicago area, and a note upon a guest ant associated with



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198 .Psyche [September
dkei colonies at Palos has been published (Park, Thomas, 1929).
Formica ulkei colonies are also established at Palatine, Illinois, some thirty miles north-west of Chicago under the same general ecological conditions.
The Palatine colonies
have not been as thoroughly studied for myrmecocoles as those at Palos, this latter section having been visited re- peatedly.
A number of species of insects have been taken from the ulkei colonies. These species have been determined as fol- low~,~ and the locality records given in order to supplement as much as possible the account of Holmquist (1928 a, pp. 83-4) :
TABLE I. Myrmecocoles of Formicar ullcei Emery. HOMOPTERA
Cicadellidae
I. A nymph taken at Palos, August 4, 1929, in the lower dome galleries.
2. A neuropterous larva, very similar to the larvae of the Chrysopidae, taken in a lower gallery at Palm, August 4, 1929. It may have been brought in by the ants, or it may. have wandered in, either by chance or to feed upon aphids.
DIPTERA
Syrphidae
3. Microdon, sp.
The larvae of Microdon were usually
present in the nest, both in Palatine and at Palos, and were present in certain nests in great abun- dance on October 6, 1928, at Palos, especially in the less superficial galleries.
11 am greatly in debt to my friends, Mr. W. J. Gerhard and Mr. Emil Liljeblad, of the Field Museum of Natural History, for their care in determining and rechecking the material collected from the dkei nests.




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19291 Myrmecocoles of Formica ulkei 199
COLEOPTERA
Carabidae
4. Tachyura incurva (Say)
Abundant. Palos : October 6
and 13, 1928; April 4 and 12, August 9 and 16, 1929. Palatine: August 6, 1929. It is interesting to note that this species has also been taken in the nests of the related host, Formica exsectoides (Ulke, 1890 ; Schwarz? 1890).
5. Two small carabid larvae were taken from the lower dome galleries, one at Palos (August 16, 1929) and one at Palatine (August 6, 1929).
Staphylinidae
6. Megastilicus f ormicarius Casey. Palos : August 4? 1929. It is interesting to note a further parallel in the myrrnecocoles of ulkei and exsectoides, this staphylinid being reported from nests of the latter by Schwarz (1889).
7. Atheta polita Melsh. This species of the Myrmedoniini was abundant on October 6, 1928, in the dome gal- leries and entrances of a weak colony at Palos. This species has also been recorded from the gal- leries of Reticulitermes flavipes by Park (1929 e), and Ulke (1890) mentioned finding staphylinids allied to Myrmedonia in numbers in the nest of a species of Formica.
Leptinid~
8. Leptiws testaceus Miill. Abundant in a weak colony of ullcei at Palos, October 6, 1928.
Pselaphnd~
9. Bat~isodes globosus (Lee.)
October 6 and 13, 1928, at
Palos. In numbers on the former date.
10. B. denticollis Casey. Abundant at Palos on October 6, 1928; April 4 and 12, and August 4, 1929. 11. B. species. Palos on October 6, 1928. Cucu jidz




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200 Psyche [September
12. Cathartus advena (Waltl.) At Palos on October 6, 1928. Possibly a chance occurrence or had pene- trated the colony for hibernation.
13. Melanotus communis (Gyll.) A single adult which was still very soft and pale from pupation, taken from a nest at Palatine on August 6, 1929.
14. Phyllophaga species. Larvae, pupae and imagos taken from the Palos nests on October 6, 1928. Rather abundant.
15. P. horni Smith. One male. In lower dome galleries as above.
On October 6, 1928, thirteen Leptinus testaceus Mull. were taken from the upper galleries of a weak colony of Formica ulkei Emery. The mound was beginning to be overgrown with grasses and measured only eight inches high and some two feet in diameter. With the leptinids were taken fifty-six Batrisodes and twenty Tachyura. Since testaceus is exceptional in the mounds of ants and is not reported from those of ulkei, it was sought repeatedly but others were not seen. The original lot was carried to the laboratory with other myrmecocoles for study, and the following points were learned as to the ecology of these species :
Leptinus testaceus Mull. was isolated in a petri dish nest and thirteen workers, both major and minor, of Formica ulkei were introduced. This group was maintained for six days, the ants being fed on sugar water. During this time the beetles were not molested by the worker ants. The latter passed near or over the leptinids frequently without being visibly stimulated beyond a momentary pause in their walk, or an occasional investigatory movement of their antennae.




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19291 Myrmecocoles of Formica zilkei 201 Conversely, when a Leptinus came into contact with an zdkei worker it usually crouched to the substratum, remain- ing motionless, and seldom ran away.
Similarly, the leptinids were apparently not molested by the pselaphids (Batrisodes globosus and B. denticollis), and vice versa, nor were the pselaphids attacked by the ants. In another series of observations, leptinids were isolated with the carabid, Tachyura incurva. In one petri dish, out of three used, the leptinids were unmolested. In the other two nests, each having one Leptinus and three Tachyura, the Leptinus were completely devoured within twenty-four hours save for the meso- and meta-sterna and the elytra. Further details on the carnivorous behavior of these cara- bids will be given later, however it is interesting to note that when a leptinid was met by Tachyura in the laboratory nests it frequently darted out of the latter's path. Just what the food of testaceus consists of has been gen- erally guessed at and in view of the controversial nature of its status with its many hosts, some knowledge of its feed- ing habits should be of interest.
A simple leptinid was placed in each of six petri dish nests and given no food by the experimenter for two days. Obviously, during this time it may very well have caught and devoured small organisms in the soil taken from the ulkei nests placed in the dishes, which could not be readily removed, e.g., small acarinids (Gamasoidea?) . At the end of two days, viz., the second night, a de-
pressed slide full of sugar syrup was placed in each dish. Two of the leptinids were observed to halt at the slide. These two lowered the head and prothorax and after tap- ping about with their antennae, moistened their palpae and mandibles in the solution. The other two either went around the syrup, or turned back on their path. It is pos-
sible then, that testaceus will feed
on occasion on sugar
syrup. Mere moisture was certainly not at a premium in the petri nests as one section of the soil was kept saturated with water.




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202 Psyche [September
Formica ulkei workers, it may be added, readily took up the sugar syrup and subsequently could be seen regurgitat- ing to other workers. The pselaphids, Batrisodes, were not observed to feed on the sugar solution and often walked through, or were caught in, the syrup without being seen to take any with their mouth parts.
In view of these data, it is possible that testaceus, under the proper conditions, feeds on the honey in the nests of bumble-bees, and since its food habits are compatiable with this view, it may exhibit phoresy, being carried about by mammals from one nest of bees to another, and consequently being taken in their nests as well. This is not to say that testaceus could not exhibit carnivorous or omnivorous be- havior, nor that it could not live as both an ectoparasite and a guest, under suitable conditions.
The occurrence of Tachyura incurva (Say) in the nests of ants, especially Formica exsectoides, a host ant related rather closely to F. ulkei, has been noted by Ulke (1890), and Schwarz (1890), and its general distribution under bark and on the floor of forests is commented upon later. Despite the abundance of this species, little is known of its behavior.
Incurva apparently shows some periodicity in its appear- ance with Formica ulkei? thus some days (August 9, 1929) it was present in great numbers, several to a square foot of nest surface, running about over the surface of the mound, in the grass on the moist soil around the nest, and coming in and out of the gallery openings with the ulkei workers, especially the openings near the base of the dome of the nest. On this date it was also present in numbers within the nest itself, at the ground level and the intervening gal- leries to the most superficial ones. On other days (August 16, 1929) it was almost absent, several being taken from three nests. Again, the species would appear to frequent some nests rather than others in common with Batrisodes and other myrmecocoles. Thus one nest would yield a number of the carabids while adjacent nests would be almost devoid of myrmecocoles. I have found incurva to be the most abundant beetle myrmecoeole of ulkei at Palos,



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19291 Myrmecocoles of Formica ulkei - 203 as well as at Palatine on August 6, the only trip made to the latter locality.
This carabid appears to occupy a most fortunate position in the ulkei community. It is practically unmolested by the worker ants at all times, as mentioned before the beetles running in and out of the galleries at will, undisturbed by the ants, and occasionally becoming motionless when an ant passes them. The carabids were killed on several occasions and placed on the surface of the mounds at Palos Park, and the worker ants did not molest the beetles very much more when dead than when alive. Thus, although the ulkei were bringing in all sorts of insects, dead or alive, for consump- tion, the dead Tachyura would often be passed by a worker, occasionally investigated, and rarely picked up. In the latter case, the worker would shortly drop the beetle and walk away. This was also observed in laboratory nests of ulkei. On the other hand the larvae (Carabidae?) taken at Palos and at Palatine, when placed with ulkei workers, were pursued and one was devoured by the ants. Observation of Tachyura shows that, although unmo- lested by the other members of the ulkei community so far observed, the carabids prey at will on anything they can devour. In this they resemble the behavior of the hyaena, only attacking when their prey is dead or sufficiently dis- abled to be harmless, as the following points will indicate. In the first place, these carabids are essentially cannibal- istic, and given a dead or disabled incurva, it is seized by others if they are within a sufficiently short distance to be stimulated by the food. Apparently the beetles must be within several milimeters before the presence of food sti- mulates them, and if the latter is removed a short distance away they have difficulty in again locating it. If one of the beetles finds the food it seizes it in its mandibles and quickly hides with the morsel where it can devour it un- molested. If two or more of the beetles find the food at the same time, or discover one feeding, they immediately attempt to take the morsel away, and tug and pull the food about until each obtains a portion, or one manages to run away with the whole, of their dead comrade. Such behavior is only shown in the presence of food apparently, as the



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204 Psyche [September
species can be kept in confined quarters in great numbers and the individuals will not fight or molest one another as long as they are in good condition.
If the food is too heavy to be taken away, the incurva feed on the prey in situ. Where possible pieces are pulled off and these are taken off and surreptitiously eaten, upon which the beetle returns again for another morsel. Thus it is a common sight to the experimenter to see six to ten incurva tugging and biting at such large prey as the larger Muscidae (Lucilm, Calliphora), feeding on the fly, with the beetles distributed in a circle about the victim, each beetle with a certain section of the carcass. Under these conditions when a beetle leaves its place and attempts to dislodge a neighbor, the latter bites at the intruder and usually drives it away.
The incurva usually attack the mouth-parts of their prey first (Fig. 1) and these are sucked or licked for the moisture obtained. Before attacking such a fly, the beetle will often circle it several times, biting at the sclerites and wings in passing and then invariably settle on the moist mouth region or the membranous joints between segments of the legs and body sclertes. However, if a wound is first made in the fly, this is attacked as readily as the mouth-parts. Even more readily is a dead or disabled worker of the host ant, ulkei, attacked. The behavior is essentially the same, the beetles showing a preference for the mouth parts glistening with regurgitated fluid. If the head of the ant is crushed a drop of fluid is forced on the mouth-parts and this is rapidly devoured by the beetles, often one on one of the ant's mandibles, and a second on the other side of the head, the two biting at each other when they are too close or driving away other beetles from this region. Occasion- ally the gaster of the ant is licked, possible for the oily secretion, and the antennae and leg joints, or wounds are attacked.
The queens of the guest ant, Solenopsis molesta, living with Formica ulkei, are attacked by the latter when pos- sible (Park T. Loc. cit.) and Tachyura feeds on molesta also. Here the molesta queen is devoured in the same way



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19291 Myrmecocoles of Formica ulkei 205
that the ulkei workers are, the mouth-parts being most stimulating to the beetles.
Finally, the mouth-parts of ulkei workers have been wiped as dry as possible and then covered with a drop of saturated sugar solution. The incurva sucked or licked the mouth- parts as dry as though the fluid had been regurgitated by the ant. To see whether or not the laboratory sugar solution would be eaten if given them as such, drops of the fluid were placed on bits of paper or wood, and the incurva fought and gathered about these drops until they had eaten all of it, as though the species were accustomed to such a diet in nature.
In addition to this varied diet of incurva, the species has also been seen to devour crushed larvae and pupae of the host ant, Formica ulkei, and the myrmecocolous staphyli- nid, Atheta polita as well as attack the larvae of the syrphid, Microdon, taken from the same host nest, when the latter's soft, ventral creeping surface was exposed. From such observations one obtains a fragmentary pic- ture of the place held by Tachyura incurva in the ulkei biocoenose, viz., that of a relatively unmolested species feed- ing upon the stores of food carried in by the ulkei workers, and attacking both the host ants, and the other co-inhabi- tants of the nest when these are dead or disabled. It is pos- sible, although improbable, that the incurva may even creep up and steal some of the regurgitated fluid being given to a worker ulkei by another, as is the custom of certain synoe- ketes (Atelura formicaria), although its general habits tend to place the species in the role of scavenger. In return for this abundance of food and protection from the enemies of the carabidae (birds, toads, insectivorous mammals, and predaceous insects in general) which give the ulkei mounds a wide berth, the incurva perform the doubtful favor of aiding in removing nest refuse, a task which is ably performed by the ants themselves. Other things being equal, the temperature of the ulkei mounds is more constant than that of the surrounding



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206 Psyche [September
environment (Holmquist, 1. c.) and the galleries run to the superficial water table, and are consequently always moist, even in the hot, dry summer months. In such nests a temperature and a moisture gradient exists and either of these factors, or both, may have important effects upon the