W. L. Nutting.
Colenizing Flights and Associated Activities of Termites. I. The Desert Damp-Wood Termite, Paraneotermes simplicicornis (Kalo Termitidae).
Psyche 73:131-149, 1966.

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COLONIZING FLIGHTS AND ASSOCIATED
ACTIVITIES OF TERMITES.
I. THE DESERT DAMP-WOOD TERMITE
PARANEOTERMES SIMPLICICORNIS
(KALOTERMITIDAE)
BY W, L. NUTTING
Department of Entomology, University of Arizona INTRODUCTION. - The swarming period provides the only oc- casion when observations can be made undisturbed on, many species of termites. Flights involving large numbers of dates, apparently synchronized with particular seasons, are a conspicuous phenomenon in many parts of the world and well known to local inhabitants. Yet only the most limited information is available on the flights of a small percentage of the commoner species, i.e. the months and time of day during which flights are staged, and perhaps an associa- tion with rainfall. Not until recent years have many real efforts been made to correlate the dispersal flights of termites (Snyder, '61) or the nuptial flights of ants (Kannowski '59; Talbot, '56; '64) - which appear to be similarly related to definite weather patterns- with even the most obvious environmental factors. The difficulties involved in gathering more detailed intelligence, however, become apparent after a season or two of field study. The following account is the result of an increasingly successful series of observations made on one of twelve different species in a single area over a period of seven years. It summarizes field notes
on 78 separate flights together with a preliminary analysis of accom- panying weather data. The ultimate objective of such a study should be the elucidation of the physical and physiological factors which trigger the flights of a species, both seasonally and daily, over its entire range. At present the bulk of the data is climatological and far outweighs that on the behavior of the termite itself; the study is thus perforce largely descriptive. Succeeding papers in this series should gain in significance from data being gathered concomitantly on additional species in the families Kalotermitidae, Hodotermitidae, Rhinotermitidae and Termitidae. Although the actual flight stimuli may eventually prove very different from those which suggest them- selves from time to time, this descriptive state should provide a start- ing point for other more profitable approaches to the subject. 'Arizona Agricultural Experiment Station Journal Article No. 1112. Manuscript received by the editor February 25, 1966 I3 1
Pnche 73:131-149 t 1966). http:l~psycb.cnlclub.orBf73/7J- 13 1 html



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132 Psyche [June
Paraneotermes simplic'icornis is apparently unique among the dry- wood termites (Kalotermitidae) for, although the reproductive cen- ter has never been found, it is fundamentally subterranean in habit. Over its known range in the deserts from southern California and northern Baja California to southern Nevada, southwestern Texas and northern Sinaloa, Mexico', it typically attacks moist wood in or on the ground in washes and canyons. Small living trees are even cut off just beneath the soil on occasion. A detailed account of the biology, distribution and taxonomic relations of this most interesting termite was published by Light in 1937. At that time swarming had never been observed, nor has it been reported since. STUDY AREA AND METHODS. -Nearly all the flights were ob- served within an area of less than an acre in north-central Tucson, Arizona, at an altitude of 2400 ft. This part of the valley floor is now about equally divided between creosote bush desert (Larrea tridentata) and small residential developments. Three to four feet of fine-textured alluvium overlies a narrow zone of friable caliche or hardpan. The mean annual precipitation of 10.9 inches is almost equally divided between a summer ( July-Sept.) and a winter (Dec.- March) rainy season, characteristic for most of the Sonoran Desert. Although the mean annual temperature is 19.6OC, it is of little sig- nificance unless it is realized that daily fluctuations of 15' are common and of 2iå¡ not unusual. In 62 years the highest recorded temperature was 44.4O (July, 1953, and several other dates), the lowest - 14.4OC (Jan., I 91 3) (Sellers, '60). Considering our scant knowledge of the types of sense organs with which the various castes of termites are equipped, much less the in- formation which they are collecting, it is still far from clear what environmental factors should be measured, to say nothing of the necessary degrees of accuracy. Hence, many of the methods used here are admittedly exploratory and probably crude. Certain refine- ments have already been made and others are continually suggesting themselves. For example, it would probably be desirable to measure many microclimatic parameters ; however, their usefulness will de- pend upon a much greater knowledge of the termites and their pre- flight activities within and near the nest than is now available. Starting in January, 1960, continuous records of air temperature and relative humidity have been made in the study area with a Ben- dix-Friez Hygrothermograph, Mod. 594 (maintained to an accuracy within approximately 2 iå¡ from - 12 to -I- 43OC and å±5 from o to 100% RH). The instrument is sheltered six feet above the ground. Weekly mean temperatures and relative humidities were



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19661 fitting - f'araneoter?nes 133
figured from the hygrothermograph records with the aid of a plani- meter (Cutright, '27). Evaporation data are available (U. S. De- partment of Commerce, '62; '63) from measurements made daily at 5 :00 PlM on the campus of the University of Arizona, Tucson, 2.5 mi. SSW of the study area. Saturation deficit was calculated for time of sunset plus 15 minutes at Tucson, and for certain other times, on the basis of hygrothermograph records. Rainfall was meas- ured daily with a simple plastic collecting gauge near the center of the area from midnight to midnight. Illumination at the zenith was measured several different times with a Weston photographic ex- posure meter (Master 11, Mod. 735). During 1962 barometric pressure was continuously recorded on a temperature-compensated Taylor recording barometer. Some observations were made on flights from a laboratory colony in an 8 X 8-foot walk-in refrigerator which was equipped with a Partlow recording temperature program control (Mod. RCS) capable of providing any desired daily or weekly temperature pattern. All times are Mountain Standard and based on the 24-hour clock.
DEVELOPMENT OF ALATES AND PRE-FLIGHT BEHAVIOR. - Light '37) termed the large aggregations of nymphs and soldiers of this species "temporary outposts" 01- "foraging s~~bcolonies"; no repro- ductive~ of any form, eggs or small nymphs have yet been found in them. Samples from 19 subcolonies collected in or within 25 miles of Tucson have revealed subimaginal nymphs (with large wing pads) to be present between August 30 (1962) and May 20 (1961). On the latter date an entire subcolony was removed from a large timber beneath the steps of a farm building and set up in a laboratory ob- servation nest. It contained 39 soldiers and 760 nymphs, many of them pre-alates. Between June 2 and 15, all of these had developed into 130 alates at laboratory temperatures only slightly less variable than, and averaging a few degrees below, those outside. By a most fortunate coincidence another subcolony was found on June 14, 1961, in the roots of a dead palo verde tree fCerciidu7n microphyllum). It contained 104 soldiers, at least I IOO nymphs (no re-alates) and 190 alates. No flights were observed in the Tucson area in 1961 until July 5, although it is likely that this was not the first flight of the season. The above evidence shows an abrupt and rapid mass develop- ment of alates within three weeks, probably less, of the first flight. Although no local soil temperature records are available it seems reasonable to assume that this maturation is a direct result of the intense heating of the soil which occurs during the very clear, dry months of May and June. Monthly mean air temperatures increase



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134 Psyche [June
rapidly from 18.iå¡ in April to 22.4' in May, ~7.6~ in June and 30. I O in July (Sellers, '60) .
Light ('37) reported alates in colonies in California from late October into November and in Nevada during May. Snyder ('54) noted that alates were taken from a colony in Texas in mid-April. In the absence of flight records from these regions speculation is unprofitable, although flight schedules are probably shifted in con- formity with local weather patterns which result from altitudinal and latitudinal differences over its entire range. Once alates are present in a colony, the influence of biological factors on the initiation of flights must also be considered. Although the behavioral interactions among the members of a colony have only begun to be fathomed, the feverish activity exhibited within a colony at the onset of conditions favoring flight has probably been noted many times (e.g., in Kalotermes [=Incisitermes] minor Hagen by Harvey, '34, p. 221). In this connection some early attempts were made to induce flights from a large sub-colony which had been in the laboratory for about a month. It was confined in an observa- tion nest of seven plastic petri dishes interconnected with pollyethylene Figure 1. Flight season of Paraneotermes simplicicornis in relation to rainfall, weekly mean temperature and relative humidity at Tucson, Arizona, in 1962. Dates showing 0.1" actually indicate amounts from a trace to 0.1" of rain. Flights began when mean temperature remained above about 23OC. The upper section shows the numbers of alates observed on each date during the flight season from June 9 to Sept. 7.



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19661 'Nut- - Paraneoter?nes 135
tubing and placed on a large tray of moist soil. (Paraneotermes has been maintained for more than a year in this type of nest with the petri dishes containing a layer of 4% agar and thin slices of wood.) The colony was held in the dark, walk-in refrigerator for about a week at 27OC and 30% RH prior to a brief, simulated flight season. Observations were made with the program control set to duplicate the temperature cycle of five consecutive days of typical summer weather. Daily temperatures varied between 22O and 43OC, relative humidities between 28 and 78 %. Temperature peaks occurred be- tween 1500 and 1600 each day. During the middle of these days the temperature sometimes rose at a rate of about 3.3OC per hour and fell later by as much as gå¡ per hour for short periods. No measurements were made within the nest, although it is certain that the relative humidity was continuously at or dose to saturation. Most of the observations were made under a red light. Under such conditions and below about 34OC, activity in the colony appeared to be normal, with the alates remaining almost motionless in one or more tightly packed clusters. As the temperature rose between about 34O and 36OC, the general activity gradually in- creased; the alates began to run about and the clusters broke up. Above about 36OC the entire colony became more and more agitated and the alates leaped and fluttered their wings in frenzied excitement. As the temperature dropped this behavioral sequence was reversed. In the range from 38O to 36OC, the alates again became gregarious i n one instance within 15 minutes from their peak of activity. On three days, small numbers of these excited alates (15, 13, 2) actually emerged from ihe nest through a small hole drilled in the cover of one petri dish as well as from under the edge of the cover. In the latter case two soldiers were obviously and attentively stationed near the point of emergence although they did not appear to be iegulating the exit of the alates as suggested for Kalotermes (=In- cisiterm es) minor by Harvey (loc. cit.) . The emerging alates rapidly gained high points on the soil and small stones in the tray, then took flight after much moving of heads from side to side and waving of intennae. The door of the chamber was opened and observations were terminated after the alates had made rapid, erratic flights into the day-lighted room outside.
These limited observations show that the phases of flight activity, even within the colony, are amenable to laboratory study. Although the preceding manipulations did not duplicate the environmental conditions under which this essentially subterranean termite stages its flights, they do suggest that high temperature (probably reached



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later in the day near the soil surface) may provide an important cue for the initiation of daily flight periods. As more data become avail- able further refinements in this type of experimentation are planned with several other species of termites in Arizona. FLIGHT SEASON. -According to legend in the Sonoran Desert, the summer rainy season begins on San Juan's Day, June 24. The rains are also believed to initiate the swarming season of the termites in this region; indeed, in many Latin American localities with a similar weather pattern, the swarming alates are called "Palomitas de San Juan" (Light, '34).
Legend and meager published informa-
tion led to some early and rather casual observations which resulted in one flight record for Paraneotermes on August 12, 1956; three in 1957, on July 10, I 4 and 16; and one on July 17, 1959. More persistent observation, still within the rainy season, yielded I I flights from July 5 through 29, 1961. Guided by experience of previous seasons and new knowledge that alate production may begin in early June, intensive observations were made from mid-May to mid- September in 1962 and, with the exception of six weeks of June and July, again in 1963. Thirty-one flights were thus recorded from June 9 through Sept. 7, 1962 (fig. I), while the first and last flights in 1963 were recorded on June I 5 and August I 9 (fig. 2). These records spanning 91 and 66 days attest to a considerably protracted flight season for this species, beginning well in advance of the rainy season. A flight on May 29, 1965, further expands the cumulative seasonal record to 102 days within five consecutive months. T. E. Snyder has informed me ('64, in lift.) that the U. S. National Museum contains alates caught by light trap on July 6 and August 1 5, 1947, at Blythe, Riverside Co., California. INFLUENCE OF ENVIRONMENTAL FACTORS ON TIME OF FLIGHT. - The flights of termites are considered to provide for the foundation of new colonies and hence the maintenance and dispersal of the species. Extensive observations on the termite fauna in Mexico and the southwestern United States have led the writer to conclude that matings between sexes from different colonies, in synchronous flights ever limited areas, are presumably usual. The idea that sibling matings are the rule has been advanced by several authors (Weesner, '60, p. 161) although, admittedly, either position would be equally difficult to prove. Since alates of Paraneotervzes have never been observed emerging from a nest in nature, the following factors ac- tually describe the conditions under which flights are known to have occurred. A more refined analysis does not yet seem warranted on the basis of such data, limited as they are to only two seasons. A



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19661 fitting - Paraneotermes 13 7
Figure 2.
Flight season of Paraneotermes simplicicornis in relation to rainfall, weekly mean temperature and relative humidity at Tucson, Ari- zona, in 1963.
Dates showing 0.1" actually indicate amounts from a trace to 0.1" of rain. Flights began when mean temperature remained above about 23OC. The upper section shows the numbers of alates observed on each date during the flight season from June IS to Aug. 19. No observa- tions
were made between June 24 and August 1. Data on the maturation of alates were obtained from two colonies, one in the laboratory and one in the field,
few simple correlations are apparent, however, and may provide a basis for determining the cues which are actually used by Paraneo- termes for initiating both its annual flight season and daily flight periods.
Temperature
The timing of the flight season in relation to weekly mean tempera- ture and relative humidity for two years is plotted in figures I and 2. Flights began when the weekly mean temperature remained con- sistently above about 23CC, while later in the season means reached as high as 29.9' ('62) and 30.6OC ('63). The seasons ended during weekly means of 25.9' ('62) and 25.4'C ('63), leaving three and seven weeks in these years before falling to 23OC. At this point it might be mentioned that the areas under the curves for the two years studied - taken arbitrarily from the lowest weekly mean of the winter to the date of the first flight (figs. I and 2) - are very close as measured with a planimeter. This has suggested that it



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might eventually be profitable to explore modifications of the tem- pei-ature-sumn~ation method in connection with alate development both in nature and in controlled environments, and then to relate results to the initiation of the flight season. However, the list of unknowns concerning this species is so great - location and environ- ment of the nest, favorable temperature ranges for the development of any caste, etc. -that meaningful calculations are hardly possible at present. The simplest and perhaps most plausible explanation for the termination of the flight season might lie in the fact that all dates had flown.
Figure 3 shows the flight periods in relation to the following daily temperatures during the season in 1962; minimum, maximum and temperature 15 minutes after sunset. Daily flight periods (29 in 1962, 11 in 1963) occurred on days with a mean minimal tempera- ture of 20.1~ (range, 12.0 - 24.8) in 1962, and 19.0' (range, 13.7 - 22.0) in I 963. The mean maximal temperature for the same days was 33.3O (range, 26.9 - 37.6) in 1962, and 32.3' (range, 29.5 - 36.7) in 1963. Flights began each day at approximately 15 minutes after sunset; the mean temperature for this time, on the days when flights occurred, was 28.2O (range, 23.4 - 32) in 1962, and 26.0å (range, 23.7 - 29) in 1963. Within these limits there is no readily apparent relation to daily temperature patterns. The temperature cycle of a "typical day," together with curves J
-I0 0 = Fiiqht
R = Rain
W = Wind
10 20 30 10 20 30 10 20 30 5
1 n t . D t 8 t ~ s . ~ ~
JUNE
I
JULY AUGUST ' SEPT.
Figure 3. Flight dates of Paraneotermes simplicicornis in relation to daily temperature fluctuations in Tucson, Arizona, in 1962. Flights began at approximately 15 min. after sunset. Rain or wind may have prevented flights on at least 15 evenings.




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for relative humidity and saturation deficit, is presented in figure 4. The combinations of temperature and relative humidity at the time of sunset plus 15 minutes are plotted in figure 6. Daily flights almost always begin while temperature is falling steadily and generally near or shortly after the low in humidity for the day. Moisture
Rainfall and Soil Moisture. - The relation of the flight season and the daily flights to rainfall for 1962 and '63 is shown in figures I and 2. For these years, where the first and last flights were estab- lished with reasonable certainty, the flight season began' well in ad- vance of the summer rains. In 1962 the first flight was staged 81 days after the last measurable rain of 0.09'' was recorded on March 20. Eight, flights had occurred before the next measurable rain (0.02") had fallen 99 days later. The next year, 51 days elapsed between the last measurable rain of 0.58" on April 25 and the first flight, with at least three flights occurring before the first measurable rain (o.01") in 69 days. In 1965 the first flight took place I 7 days after 0.01" was measured on May 12. These records established beyond any doubt that Paraneotermes does not begin swarming in response to seasonal rainfall. This is apparently the case with many dry-wood termites, such as Cryptotermes (Weesner, '60, p. 160). Although a few of the larger flights have taken place on days fol- lowing substantial rains, the general pattern seems to be one in which rain is actually avoided (figs. i and 2). Of 29 flights observed in the study area during 1962, only eight occurred on rainy days, and on each of these days only 0.05"' or less was measured. Further, flights did not take place if any rain occurred within an hour before or after flight time. A similar pattern is evident for other years, although the data are much less complete. No measurements of soil moisture have been made in connection with the flights of this termite. It is certain, however, that the gen- eral floor of the desert is hard-packed and that the soil is extremely dry to a depth of many feet during the early part of the season. The matter of the selection of nesting site is briefly covered under Post- Flight Behavior.
Relative Humidity. - Figures I and 2 show the relation of the total flight season to the weekly mean relative humidity for two years. The seasons took place within means of 50. I and 79. I % ('62) and 40.6 and 86.9% relative humidity ('63). These ranges include very nearly the extremes for each year, and cover the summer trend from very low to high mean humidities.




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Psyche
Figure 4. Relationship between approximate flight time (sunset plus 15 min.)
of Paraneotermcs simplicicornis and temperature, relative humidity, saturation deficit and evaporation. June 20 was taken as a typical day during the 1962 flight season in Tucson, Arizona. In relation to daily fluctuations of relative humidity, individual flight periods (29 in 1962, I I in 1963) occurred as follows : on days with a mean minimum humidity of 45.8% (range, 37 - 65) in 1962, and 47.4% ( range, 30 -- 65 ) in 1963 ; on days with a mean maxi- mum humidity of 85.9% (range, 62 - 100) in 1962, and 91.4% (range, 65 - 100) in 1963. Mean humidity at flight time (sunset plus I 5 minutes) was 56.8% (range, 38 - 92) in 1962, and 71.3% (range, 36 - I 00) in 1963.
When the rains begin, usually in July, fluctuations in relative humidity vary widely during each day as well as from day to day. There were several days during the two years studied when the relative humidity at the time of sunset was at or close to 100%. Daily flights of Paraneotermes almost never occurred on such days; indeed, probably as a result of its avoidance of rain, it rarely flew



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19661 fitting - Paraneoter?nes 14I
when the relative humidity was as high as 80 or 90%. It is hardly necessary to point out that the relative humidity at the time of flight, generally well below 60%, is closely correlated with the high tem- peratures during afternoon and evening (fig. 4). Evaporation and Saturation Deficit. - Since evaporation was measured 2.5 miles from the study area, the following figures are included only as a general indication of the evaporative power of the atmosphere in a region occupied by Paraneotermes. Figure 5 shows that flights occur during the season with the highest evaporation rate of the entire year. The mean daily evaporation rate for 29 flight days in 1962 and I I in 1963 was 0.36" (range, 0.10 - 0.51) in 1962, and 0.30" (range, 0.10 - 0.56) in 1963 (U. S. Department cf Commerce, '62 ; '63). The overriding influence of high tempera- ture at this time of year insures a high level of evaporation in spite of the moderating effect of the rains which are, at best, sporadic and only infrequently heavy.
The saturation deficit at the study site provides another measure of the dryness of the atmosphere which the alates encounter during their brief period of actual flight. Also closely dependent on tem- perature, this factor varies about a very high level during the flight season. The weekly mean saturation deficit for the approximate time of flight (sunset plus 15 minutes)
is plotted in figure 5. In
1962 the 29 daily flights began at a mean saturation deficit of 12.8 mm. Hg (range, 2.1 - 20.7 mm. Hg). The typically wide daily variation in saturation deficit is shown in figure 4. Although this information may be of little value at present, laboratory experiments might be designed to determine whether the alates respond to differ- ences in relative humidity or in evaporation (or saturation deficit), and thus provide a means for evaluating the effect of these factors on flight behavior. For example, perhaps the contrast between a relatively dry atmosphere and the higher moisture levels in micro- climates at the level of the soil provides gradients which are used by the alates, first in leaving the colony and later in seeking out suitable nesting sites.
Light
The rather consistent appearance of alates at lights in the early evening for several seasons suggested that light intensity might be a cue for the initiation of daily flight periods. The times of "first sightings" of alates during 1962 are shown in relation to time of sunset for Tucson in figure 7. Starting in 1963, measurements of light intensity at the zenith have been made with a photographic light



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meter on a number of evenings during: each flight season. Para- neotermes has never been observed in flight until the light intensity has thus registered approximately 0.5 lumen per square foot (foot candles) or less. As with Neotermes tectonae Damm. (Kalshoven, '30) and probably other evening fliers a few observations have shown that flight time is earlier on cloudy evenings. Considering the handi- cap of unknown nesting sites, the correlation between the beginning of the flight period and the time of sunset, or light intensity, is close. Whatever other advantages there may be, it is certain that many predators must be avoided by swarming at dusk. These few notes indicate the desirability of continuous and more sensitive measurements of light intensity in the vicinity of the emer- gence holes, whenever they can be found. The subject of rhythms and other aspects of behavior in the alates, nymphs and soldiers should also be studied in laboratory colonies under controlled illumination.