W. S. Creighton and R. E. Cregg.
Studies on the Habits and Distribution of Cryptocerus texanus Santschi (Hymenoptera: Formicidae).
Psyche 61:41-57, 1954.

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PSYCHE
Vol. 61 June, 1954 No. 2
STUDIES ON THE HABITS AND DISTRIBUTION OF CRYPTOCERUS TEXANUS SANTSCHI
(HYMENOPTERA : FORMICIDAE)
BY W. S. CREIGHTON, City College, New York and
R. E. GREGG, University of Colorado
In recent years Dr. M. R. Smith (1,2) and Fr. W. W. Kempf (3,4) have published papers on the genus Cryp- tocerusl. These studies deal primarily with taxonomy and do not supply many data on the habits of the ants of this genus. The habits of Cryptocerw texanus, the only mem- ber of the group whose occurrence in the United States can be regarded as abundant, thus remain largely unknown. From the fall of 1951 to the spring of 1953 the senior author took twenty colonies of C. texanus in southern Texas and northeastern Mexico2. Three of these colonies were studied in artificial nests for several weeks and later three more colonies were sent to the junior author for further observation. One of this second group of colonies was still alive a year afterwards when this paper was sent to press. The habits recorded here were largely deter- mined from studies made on these six colonies. 'The writers have appealed to the International Commission on Zo- 6logical Nomenclature to have Emery's use of the generic names Ceph- alotes and Cryptocerus sustained. Until a decision has been handed down we prefer to use Emery's system. The name changes advocated by Dr. Smith have already caused regrettable confusion in this group. "Fieldwork done on a Guggenheim Fellowship. ?.
41
Psit-fie 61:41-57 (1954). hup ttpsychc rinclub orgt61t61-04Lhtml



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42 Psyche [June
Before discussing these studies it seems advisable to present certain general observations on Cryptocerus tex- anus. In the paper which Dr. M. R. Smith published on texanus in 1947 (1) seventeen stations were listed. Only six of these carried notations as to the nest site of the Figure 1. Cryptocerus texanus: a, lateral view of the head of the major; b, sculpture of the cephalic disc on the head of the major, showing the rectangular, silvery, longitudinally grooved hair in each foveola. Figure 1, a, is drawn to a scale twice that of plates 3 and 4. colony. Of these six only one referred to a nest in a live- oak tree. On the basis of the above data it would be unlike- ly for anyone to conclude that texanus prefers to nest in live-oaks. Nevertheless, this appears to be the case. Pre- sented below is a list of trees in which texands had been found nesting. This is a composite of the data publi'shed by Dr. Smith and those more recently secured by the senior author. In two cases the information reported by Dr. Smith



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19541 Creighton and Gregg - Cryptocerus texanus 43 has been interpreted on the basis of probability so that it fits into the list. Thus his nest reported from "persim- mon" has been assigned to Brayodendron and that said to have come from a 441ive-oak" has been allocated to Q. virginiana.
1. Quercus virginiana (live-oak) 14 colonies 2. Quercus fusiformis (live-oak) 3 colonies 3. Quercus stellata (deciduous oak) 2 colonies 4. Zygia flexicaulis (Texas ebony) 3 colonies 5. Brayodendron texanum (Mexican persimmon) 2 col- onies
6. Xanthoxylum clava-herculis (prickly ash) 1 colony 7. Celtis pallida (hackberry)
1 colony
8. Prosopis juliflora (mesquite) 1 colony Of the twenty-seven colonies listed above seventeen (63%) came from live-oaks. It thus appears that texanus definitely prefers to nest in live-oaks, although it is suffi- ciently flexible in its nesting habits to accept other trees as well.
The size of the colony and the number of dealated queens present are also matters of interest. Four of the colonies taken by the senior author were plainly fragmentary and these have been omitted from the list below. Female
1. 1
2. 6
3. 1
4. 3
5. 5
6. 2
*
/. 2
8. 1
9. 22
10. 5
11. 3
12. 0
13. 0
14. 1
15. 7
16. 2
Major
8
1,o
19
12
25
13
6
17
13
18
8
46
9
8
10
1
Media &
Minor
22
73
56
52
6 1
37
53
53
115
55
25
186
28
31
32
26
Total Station
Lapara Creek, Texas
11 1 1 ? 7
J1 ? is
91 31 J ?
Hochheim, Texas
7; Ì
Floresville, Texas
Gambel Creek, Texas
Sealy, Texas
Iturbide Canyon, Nuevo Leon
Ì 1 ? 1 7 1 1
)? 5 17 >?
Ì 1 Ì 11
El Pastor, Nuevo Leon
Belmont, Texas
11 1 1




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44 Psyche [June
Two facts are shown by the above figures. The colonies of texanus are always small and they are often pleometro- tic. It may be stated that most of the above colonies came from separate trees. The chance that a colony of texanus may be polydomus was constantly kept in mind. Hence colonies taken in closely adjacent limbs or at separated intervals in the same limb were treated as parts of a single nest. It may be, therefore, that the relatively large totals in colonies 9 and 12 represent more than a single colony. The outstanding point of interest in the biology of texanus is the possibility that the major may serve in a phragmotic capacity. A good deal of what has been said on this subject seems to have been published without much idea of certain structural features which are involved. In order to make these features clear the junior author has prepared figures of the female, major and minor of Cryp- tocorm texanus (Pis. 3 and 4; text-figs. 1 and 2). Refer- ence to these figures will show that the prominent cephalic disc present in the female and major of texanus, does not cover all of the upper surface of the head. Projecting rear-
ward beyond this disc are two conspicuous occipital angles. Although these angles lie below the level of the rim of the disc they cannot be disregarded for they, and not the rounded posterior rim of the cephalic disc, determine the size of the aperture into which the head can be thrust. Behind these occipital angles stand the even more prom- inent humeral angles of the thorax. In the figure of the major considerations of perspective have made it neces- sary to show these angles as wider than the head, for the latter lies below and in front of them. But, even disre- garding the matter of perspective, the maximum width of the dorsum of the thorax at the humeral angles equals or slightly exceeds the maximum diameter of the cephalic disc. It follows that the thorax of the major and the female of texanus (at least at the humeri) is fully as wide as the head and often a little wider than the head. It further follows that the diameter of a passage which the texanus major can occlude is determined as much by the width of the prothorax as it is by the size and shape of the cephalic disc. The failure of previous investigators to grasp this fact has been the cause of confusion in the past.



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19541 Creighton and Gregg - Cryptocerzis texanw 45 The first person to suggest a phragmotic function for the major of Cryptocerus appears to have been W. M. Wheeler. In 1905 (5) Wheeler stated that the nest entrance of sev- eral colonies of Cryptocerus va*, which he had found in hollow twigs in the Bahamas, was always exactly the size and shape of the cephalic disc of the major. Wheeler made no claim that the major blocks the nest entrance with its head, but the implication that it does so was clear and this seems to have been the basis for later views expressed by Wheeler in 1910 (6) and by Emery in 1922 (7) that the major of Cryptocerzis is probably fphragrnotic. But no Figure 2. Dorsal view of the head of the minor of Cryptocerus texanus. Drawn to the same scale as figure 1, a.
positive statement was made on this point until 1942. In that year a posthumous paper by Wheeler (8) which had been prepared for publication by Dr. Joseph Bequaert, definitely made such a claim in the case of Cryptocerus 'pollens (the variety porrasi) and C. setulifer. The state- ment concerning paliens is as follows :
"Its habits are similar to those of Colobopsis. The ellip- tical nest entrance is guarded by one of the soldiers which occludes the orifice with its disc-shaped cephalic disc just as the Colobopsis soldier uses the truncated anterior sur-



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46 Psyche [June
face of the head for the same purpose. The cephalic disc in old soldiers and in the mother queen of the colony often becomes coated with dirt and extraneous particles so that it closely resembles the bark of the plant." The most recent note on the phragmosis of Cryptocerus is that which Kempf published in 1952 (4). Kempf's single observation on Cryptocerus mculatus failed to show the behavior cited by Wheeler. It was not until Kempf had enlarged the small nest entrance that any majors were seen. These majors, which were well inside the nest, then tried to occlude the passage which Kempf had opened up by standing "side on side". Kempf recalled that a similar compound shield, consisting of the approximated heads of several minor workers, was reported for a colony of Ceph- alotes atratus by Santschi in 1919
(9). The date of this
publication is incorrectly given by Kempf as 1929. Kempf
was clearly aware that neither Santschi's observation on atratus nor his own on maculatus are comparable to Wheeler's statement of the phragmosis of the major of pallens. But the writers agree with Kempf that clarifica- tion is needed in the case of Wheeler's 1942 statement. The major of Cryptocerus is undoubtedly phragmotic, but it is misleading to say that it behaves just as does the Colobop- sis major. The notable differences which mark the reac- tion of the Cryptocerus major are discussed in the follow- ing pages.
The junior author's colonies were housed in the modi- fied Janet nests used in
earlier studies on Pheidole (10).
These nests gave little opportunity for studying the phrag- mosis of texanus, since they lacked restricting passages. In order to study this response two other types of nests were used, both of very simple construction. The first con- sisted of two glass vials with the bottoms removed. These vials were held together by a cork, which was forced into the neck of each vial until the two rims touched. On one side of this cork a groove was cut which approximated the size and shape of the cephalic disc of the major as closely as possible. The open end of each vial was plugged with cotton after the colony was installed. The second type of nest was a small, plaster one, cast over a microscope slide.



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19541 Creighton and Gregg - Cryptocerus texanus 47 After the plaster hardened the slide was removed and suitable chambers and passages were cut in the plaster. The slide was then put back in place and held in position with rubber bands. In both these nests the action of the major in the passages could be easily observed and the passages could be enlarged when necessary. Figure 3. a, lateral view of the major of Crvptocerus texanus in the phragmotic position in a hollow twig; b, cephalic disc of above rnaiui- seen in full-face view.
It soon became apparent that if the passages were made to fit the cephalic disc of the major closely, this caste would not enter them at all. Since the medias and minors would use such passages freely there was no reason to suppose that anything other than the size of the passage determined the refusal of the majors to use them. When such passages were enlarged the majors used them without hesitation. But this behavior indicated that the major of texanus can- not or will not go into a passage whose size and shape closely approximates that of the cephalic disc. The reason for this appears to lie in the fact that the major of texanus occludes the nest opening not only with the cephalic disc



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48 Psyche [June
but with the humeri
of the thorax as well. The head of
the major of texanus can be lowered until its long axis is at right angles to the long axis of the rest of the body. Al- though many majors die in this position it is rarely as- sumed by the living insect, presumably because in such a posture the anterior edge of the head is so far below the level of the coxae that the insect would have to stand on tiptoe to keep the mandibles clear of the substrate. Con- versely, the head of the major can be raised until its long axis is parallel to that of the rest of the body. Under such circumstances the rim of the cephalic disc lies at the same level as the dorsum of the thorax. But in this position the head of the major does not occlude the passage for there is then a considerable space below the ventral surface of the head. To occlude the passage the major must lower the head until its anterior edge is on or near the floor of the passage. But when the head of the major is in this position, with its long axis forming an angle of approxi- mately 120' with the long axis of the rest of the body, the posterior rim of the cephalic disc is well below the level of the humeral angles. Thus if a major of texanus is to occlude a passage, this passage must be large enough to accommodate not only the cephalic disc but also the humeral angles above and behind it. For if the head is lowered enough to form an effective barrier there is no way in which the humeral angles can be brought down to the level of the posterior rim of the cephalic disc. It would appear, therefore, that it is physically impossible for the major of texmus to occlude a passage whose size closely approxi- mates that of the cephalic disc.
It may be readily appreciated that the situation just de- scribed is wholly different from that which marks the major of Colobopsis. In the cork-shaped head of the major of Colobopsis maximum occlusion occurs when the long axis of the head is parallel to that of the rest of the body. In this position the truncated anterior face of the head is presented to the exterior. Since the diameter of this truncated portion exceeds that of any other part of the EXPLANATION OF PLATE 3
Cryptocerus texanus, dorsal view of the major.



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50 Psyche [June
insect, it follows that the head of the Colobopsis major can be thrust into close-fitting apertures without putting the rest of the insect into an impossible posture. We may now consider the method by which minors of texanus are admitted to the nest. When the guarding major has assumed the phragmotic position the lower rim of the head usually projects slightly beyond the edge of the nest entrance. The antennae are held at either side of the cephalic disc and are clearly visible from the outside. The returning minor may or may not touch the antennae of the guard, although it usually does so. Thereafter the guard crouches down. This brings the anterior rim of the head below the level of the floor of the passage or, if the guard stands completely inside the passage, the front of the head is raised as the guard crouches. The dorsum of the guard's thorax is now no longer close to the roof of the passage and the minor can, if it is sufficiently active, wriggle be- tween the dorsum of the thorax and the roof of the pass- age. This action is seldom completed without considerable struggle on the part of the entering minor and at times the major will cease to crouch before the minor has gone through and pin the minor between its thoracic dorsum and the roof of the passage. The senior author has seen minors thus trapped who, perforce, remained in this awk- ward position for several minutes until the major would crouch again and release them. If the passageways are made large enough to accomodate two majors simultaneous- ly, they ordinarily assume a position where they are back to back. Under such circumstances the two opposed ceph- alic discs form a V-shaped area. The bottom of this V is open but the space behind it is closed by the closely ap- proximated thoracic dorsi of the two guards. When minors are admitted to the nest both majors crouch and the enter- ing worker struggles through the narrow space between the thoraces of the guards. It seems scarcely necessary to state that there is no part of this behavior which at all resembles that of the Colobopsis major, which must back away from the nest entrance to admit the returning minor. EXPLANATION OF PLATE 4
Cryptocerus texanus, dorsal view of dealated female.



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52 Psyche [June
Two other habits of the major of texanus may be men- tioned. It should be apparent that when a major is in a closely confining passage its head has much the position of the blade of a snowplow. The concave surface of the cephalic disc slopes forward and downward and its lower rim is close to the floor of the passage. When a major moves forward along a passage any minors which are in it are pushed ahead of the advancing major unless they are active enough to force their way between the thoracic dorsum of the major and the roof of the passage. This sometimes leads to rather surprising results for workers clustered within the nest entrance may be suddenly ejected from the nest by the advancing major. Before assuming its phragmotic position the major often comes out of the nest entirely. After exploring the area immediately around the entrance it backs into the passage. This is never true of minors who always go through the nest entrance head first.
Much remains to be learned about the feeding habits of texanus. In 1947 M. R. Smith published the statement that our species of Cryptocerus feed "largely on honey dew or the flesh of small arthropods9'(2). This may be true but the writers were unable to discover any food for which the captive colonies showed much relish. They refused mealworms and termites, even when the latter were torn open to expose the tissues. High protein foods such as peanut butter and cheese were also refused. This would seem to indicate a distaste for a protein diet but other observations contradict such a view. While the ants re- fused pure honey they accepted honey mixed with egg yolk. In one instance an injured female was accidentally included when a colony was installed in an artificial nest. The gaster of this female had been broken open and her own workers promptly proceeded to eviscerate her. The
gastric contents were completely cleaned out in a few hours. This action may have been due to some improper condition in the artificial nest and the food in this case can scarcely be the regular dietary staple of the insects. Yet it can be stated that was the only instance where the workers seemed at all interested in what they were eating. Other foods which were refused were pears, apples and



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19541 Creighton and Gregg - Cryptocerus texanus 53 jelly. Bananas were accepted by some colonies but rejected by others. The most generally acceptable food seemed to be maple syrup. Thils suggests that the insects may pos- sibly feed on the sap of the trees in which they live. If this is the case it is probable that such a diet is augmented by other food, for the workers of texanus forage on the surface of the ground, which they would scarcely do if the diet was entirely confined to sap. Whatever the natural food of texanus may be it seems certain that it is not sticky. Both writers found that it was inadvisable to leave sticky food in the nest for any length of time, since a num- ber of minors were certain to get caught in it. The other workers make no effort to free their trapped nestmates, who ultimately die.