Category Archives: Research

This category includes all my research projects.

Shading Comanche Harvester Ant Colonies: temperature and activity level

I extended the shading experiment to include measurement of several temperatures and also noted the activity level of the colonies.

Background:  Because most ant species nest in the ground, soil temperatures directly affect the development and survival of ants. Soil and ground surface temperatures may have direct effects on adult ant activity levels because such temperatures affect their metabolic rates. Within a tolerable range, adult ants are expected to increase their activity with an increase in temperature. For day active ants, the nest looses heat and metabolism slows over night. In the morning, adult ants warm up in the first few centimeters below the soil surface. As the soil continues to warm over the morning, more ants become active, the number of foragers increases, and foraging rate increases. These behavioral changes are easily observed for the Comanche harvester ant (Pogonomyrmex comanche). So, the questions are: how does temperature change within the nest and how do such changes affect ant activity exterior to the nest?

Methods: I measured air, surface, 10 cm depth, 20 cm depth, and 30 cm depth temperatures and recorded the kind of ant activity and its rate three times a day over three days for each month from June through November 2012. General linear models were constructed and evaluated in R.

Activity level was evaluated on a ranked scale: 0 = no activity; 1=nest maintenance and slow movement; 2=foraging; and 3=foraging and quick movement (lots of ants).

Results: The best model included air temperature and surface temperature but only explained 4% of the variance.


Canopy used in shading experiment

Shading Ant Nests Experiment

Background: Several species of Pogonomyrmex ants will alter the exterior nest area (nest yard) or move their nests if the area becomes shaded. Shading may alter the internal nest temperature and thereby effect both the metabolism of workers (how quickly they can become active) and the development of the young (eggs, larvae, and pupae).

The Comanche harvester ant (Pogonomyrmex comanche) nests in prairie characterized by oak motts of various sizes and surrounding oak forest. Comanche colonies do not nest within the oak motts nor the forest and are rarely within 5 meters of the oak forest border. I have observed these ants moving to new nest sites several meters from the original nest site. Carlson and Gentry (1973) found that Pogonomyrmex badius moved their nests in response to shading. I wondered if shading might be a factor determining nest movement for the Comanche harvester ant as well. And thereby, impacting the spatial pattern of colonies within the prairie.

Methods: This experiment was carried out in two areas of Todd Island at the Fort Worth Nature Center and Wildlife Refuge in Fort Worth, Texas, from June through November 2012.

I made canopies of canvas using PVC tubing as a framework and placed these over nests chosen to be shaded. I chose 8 nests to be shaded and 8 nests to be controls, unshaded. I monitored the nests for temperature, movement of the entire colony to a new nesting site, and movement of the entrance.

I measured temperatures 3 times a day at the beginning of each month using a Magellan 600 Explorer GPS unit and a soil thermometer probe. The temperatures measured were: air, surface, 10 cm depth, 20 cm depth, and 30 cm depth. Activity level of the colonies was also observed when the temperature measurements were made.

The canopies measured 40 cm X 40 cm and were placed 20 cm above and centered over the nest entrance. The canvas was attached to the framework using twine. To secure the canopy in place over the nests, wooden rods were placed in the soil and the legs of the framework were placed over these. Canopies were left out for the duration of the experiment.

The data were analyzed with Fisher’s Exact Probability Test and Chi Square Test.

Results: There was no significant effect of the canopies on the frequency of colony nor entrance movement.

Chi Square Results
Phi Yates Pearson
+0.04 0.06 0.23
p values 0.81 0.63
Fisher’s Exact Probability Results   p values
  One-tailed Test 0.41
  Two-tailed Test 0.82

However, there was an impact on colony activity due to the shading during midday and later. The canopies kept the surface temperature low enough for nest maintenance activities to continue through the hotter part of the day. Colonies that were shaded remained active during the hot midday when other colonies were inactive (with no ants on the exterior nest yard). The shaded colonies continued with nest maintenance activities only — mostly bringing soil to the surface. No foraging was taking place for any colony from midday on.

Conclusion: The impact of shading on the internal nest temperatures does not appear to be a significant factor for Pogonomyrmex comanche colony movement. Despite what has been observed for other species in this genus, this is not entirely surprising since 1) Texas is hot and in summer, the soil surface is too hot for the ants to walk on much of the day and 2) these ants nest in prairie associated with oak forests, so most nests are shaded at least part of the day. Field observations indicate that colonies are likely to have different activity periods based on when that colony is shaded.

Literature: Carlson, D. M. and Gentry, J. B. 1973. Effect of shading on the migratory behavior of the Florida harvester ant, Pogonomyrmex badius. Ecology 54: 452-453.



This is a sandy soiled prairie in the Southwest Nature Preserve in Arlington, TX. The Comanche harvester ant, Pogonomyrmex comanche, has about 50 active colonies in this area.

Preliminary Identifications for the SWNP – prairie ants

Here is a list of the ant species, tentatively identified for the Southwest Nature Preserve, Arlington, Texas — from the prairie site where the Comanche harvester ant is nesting.

Crematogaster lineolata

Dorymyrmex flavus and D. sp.

Forelius mccooki

Nylanderia arenivaga and N. vividula

Pheidole sp. (only minors)

Pogonomyrmex comanche

Solenopsis xyloni and Solenopsis sp. (Diplorthoptrum group, thief ants)

Trachymyrmex turrifex


Preliminary Ant Ids for the Southwest Nature Preserve

I have worked through the woodland sample from the Southwestern Nature Preserve, Arlington, Texas. Not many ants were in this sample, possible due to the continued heat.

I found

Crematogaster lineolata (acrobatic ants)

Aphaenogaster carolinesis  (I am pretty sure)

Pheidole – no species id yet (new to me) (big headed ants — definite majors and minors)

Temnothorax — not species Id yet (new to me; perhaps new find for Texas)

and one Pogonomyrmex comanche de-alate queen who may have been working as a forager for her natal colony (too late for her to be a newly mated queen). (the Comanche harvester ant)


The prairie sample has a lot more ants in it — which I found a bit surprising since it is so hot (still) now. I had thought the shade of the woodland would have allowed more species to remain active and the prairie ants would be on siesta. The traps are set out for several days in order to catch the ants whenever they are active.

Tandy Hills Prairie, Fort Worth, Texas

Addtional Sampling for Ant Assemblages

One of my committee members suggested I get more samples for my ant assemblage project. I have added three prairie sites and one woodland.

One prairie and one woodland site are in the Southwest Nature Preserve in Arlington, Texas. The Comanche harvester ant is nesting in this prairie. There are about 50 colonies of Pogonomyrmex comanche. Soil here is mixed but very sandy with some bare ground.  Currently working through these samples.

Prairie Site at the Southwest Nature Preserve, Arlington, Texas

Prairie Site at the Southwest Nature Preserve, Arlington, Texas

The woodland site at the Southwest Nature Preserve, Arlington, Texas

The woodland site at the Southwest Nature Preserve, Arlington, Texas

Today I set pitfall traps in the Tandy Hills Prairie and Stratford Prairie in Fort Worth, Texas. Comanche is not found in these sites. The soil here is dark and rocky, more clay and little sand, and no bare ground. I will collect these samples on Tuesday and see what I’ve got.

Tandy Hills Prairie Site, Fort Worth, Texas

Tandy Hills Prairie Site, Fort Worth, Texas

Stratford Prairie Site, Fort Worth, Texas

Stratford Prairie Site, Fort Worth, Texas


Comanche de-alate Queens as foragers

I am collecting more ant samples using pitfall traps to increase the sample size and  the number of different habitats for my ant assemblage study (per the suggestion of one of my committee members). I added two areas from the Southwest Nature Preserve in Arlington, Texas. One site is a mixed soil prairie site where there is a population of the Comanche harvester ant of about 50 colonies. The other is the forested site immediately beside this prairie. I will also be adding two sites from the Tandy Hills in Fort Worth and several more from the Fort Worth Nature Center. Here is the beginning data from the Southwest Nature Preserve:

I set out the traps on September 5 and collected the sample on the 8th. Looks like I have a new Temnothorax species which I haven’t been able to identify yet. I also have a de-alate Comanche queen from the forest. She cannot have been starting a new colony since these ants mate in May and June. This collection confirms my earlier observation of de-alate Comanche queens remaining in their natal nests as foragers in another population.

So far in the prairie: Pogonomyrmex comanche Dorymyrmex (probably two species), Forelius, Pheidole, Nylanderia (two species, maybe three), Trachymyrmex, Temnothorax texanus, Solenopsis (fire ant), Solenopsis (thief ant), and Crematogaster.

In the woods: Aphaenogaster, Pheidole, Crematogaster, de-alate Pogonomyrmex comanche queen, and Temnothorax.

Still working on species identifications. Of course, now I get to redo all my ordination analyses.



Prairie flowers at the Fort Worth Nature Center, Fort Worth, Texas

Ants in the Grassland: their importance and potential as indicators of ecosystem health

This is the presentation I made at the America’s Grassland Conference recently  in Manhattan, Kansas (August 2013).

I’ve posted the power point presentation below with a few additions and included the questions asked.



While we often think of ants as annoying pests, ants are important members of nearly every terrestrial ecosystem, except Antarctica. There are  perhaps 40,000 species worldwide and we have good species descriptions for about 14,000 of them – all of which are in the same family, the Formicidae.

Ants are incredibly diverse: they vary in their morphology, their behavior, their physiology, and their ecology. Ants may engineer ecosystems through their nesting and foraging habits – greatly shaping the physical landscape and thereby impacting a variety of other organisms including the plant community. Ants also have a diversity of relationships. They are important prey items as well as predators; they have important mutualistic relationships with plants, fungi, and other arthropods; they have their own parasites; they have commensals and parasites that live in their nests.

Because of all this ecological diversity, ants may be good indicators of habitats and ecosystem health. If there are changes in any of these relationships, for any of these organisms, this change may affect ant presence, activity, and abundance. Because ants are small and live on a small scale, they may detect such changes earlier than larger monitored species, such as vertebrates. Ants are also good candidates for indicators because they are easy to collect and do not have the problems of monitoring vertebrate populations which may be difficult to track, endangered or threatened species sensitive to handling, etc. The possibility for such utility has been shown in previous research.

I investigated the potential for grassland ant assemblages to be used as bio-indicators in prairies in the Fort Worth Nature Center and Wildlife Refuge in Fort Worth, Texas, including to discern habitat type and response to disturbance. I collected the ground active ants of 17 sites monthly from March – September 2012 using pitfall traps.  The 17 sites constituted a natural experiment: 3 were wooded sites and 14 were prairie sites. The sites were paired according to soil and ecological unit (from the Natural Resources Conservation Service) for wooded vs. non-wooded (3 replicates); mowed (and soil disturbance) vs. non-mowed (4 replicates); and low intensity burn vs. non-burned (2 replicates).

For each site, I measured environmental variables which are known or thought to be important to ants in choosing their nesting areas,  including depth of sand, soil penetration (compaction), depth to the restrictive layer, percent slope, drainage, percent bare ground, percent litter cover, percent standing plant cover, percent total cover, latitude, ecological units (from the NRCS), and soil type.

I used the program CANOCO to do ordination analyses: principle components analysis (PCA) on the environmental variables only and redundancy analysis (RDA) combining the environmental variables with species presence. Ant species were characterized by functional groups following Andersen (1997). The PCA confirmed that the variables chosen could be used to distinguish among sites. The RDA revealed that some of the ant species were aligned with habitats but disturbance did not matter. The sites grouped into three sets which aligned with soil types and ecological units. Some species did not align with their habitats but this may be explained by the foraging of those species into habitats other than where they nest. The RDA showed a strong relationship between the ants and the environmental variables with the interaction between percent litter cover and drainage, percent litter cover by itself and drainage by itself being significant factors. However, these factors combined did not explain more than 20% of the variation so either there are other significant factors or many factors account for the local presence of ants with none being particularly significant.

Andersen’s functional groups are problematic for these sites because some of the species placed in the groups do not have similar ecological roles as the Australian species upon which this work is based. Species richness by functional group did not vary significantly among the sites. And although the functional group designations are problematic, there is a  pattern in the composition of these assemblages with general myrmicines contributing most, followed by hot climate specialists, cryptic and opportunistic species, then tropical climate specialists and dominant species. This suggests a shape to the assemblages that may transcend individual species.

In conclusion, this project indicated weak support for these assemblages s as bioindicators and only two ants could be considered indicators of habitat: the carpenter ant species (Camponotus americanus and Camponotus pennsylvanicus) occurring in the woodlands and the Comanche harvester ant (Pogonomyrmex comanche) occurring in the Aquilla prairie.

Here the Comanche harvester ant (Pogonomyrmex comanche) forages  Pecan Sandies at a bait station in the Fort Worth Nature Center, Fort Worth, Texas

A Consideration of Andersen’s Functional Groups for North American Ant Assemblages

(These thoughts came out of an email exchange with noted myrmecologists Dr. James Trager of the Missouri Botanical Garden and Dr. Terry McGlynn of California State University Dominguez Hill).

I understand the concern that we not naively appropriate Andersen’s functional groups and the taxons that go into them – I think I have been on the verge of doing that. I obviously need to be exposed to more ant species.

My understanding is that Andersen tested dominance of the ants with bait stations and looked for aggressive interactions. Terry McGlynn’s questioning of this — that bait stations are artificial situations and do not reflect real ant behaviors/interactions well —  I think is well placed. I had thought to show that Pogonomyrmex comanche was a dominant ant in her habitat based on several observations but Dr. Walter Tschinkel, who is now on my committee, raised questions about this: what does dominance mean? I think this is a stickier issue than some believe.

For instance, there appears to be a trade-off between foragers who come early to baits and then leave and those who come later but seem to “dominate” the baits once they arrive. Are these later arrivals really dominant? I question this interpretation because of observations I have
made such as the interaction between P. comanche and a foraging grasshopper over a dead grasshopper (I have a  video) in which Comanche dealt with the competition by cutting up the grasshopper and foraging faster only at the last, stinging the offending grasshopper. When I see
Comanche dominate bait stations (photo above), I do not see the ants directly interact.

Here’s a photo of fire ant (Solenopsis sp.) at a food resource (though this was a cookie dropped in a parking lot). The fire ants seem to get to food resources quickly and to “swarm” on them effectively dominating them. I have seen fire ants overwhelm bait stations in the Fort Worth Nature Center in a similar manner. It seems a typical ant behavioral response to a desirable food resource is to dominate it indirectly by quick removal of it to the nest rather than more direct aggressive interactions which are probably more costly.

Fire ants (Solenopsis invicta or xyloni) opportunistically foraging on an Oreo cookie. I have seen this kind of "swarming" behavior on bait stations in the field as well.

Fire ants (Solenopsis invicta or xyloni) opportunistically foraging on an Oreo cookie. I have seen this kind of “swarming” behavior on bait stations in the field as well.

In the nestmate discrimination trials I am currently completing, I do not see Comanche often acting aggressively. I do see some gaster wagging in these trials. Gaster wagging is interpreted as am aggressive behavior but I am not so sure that it is always aggressive. In some situations, one ant grabs another and the one grabbed does the gaster wagging which appears more submissive. Other times, it is obvious the ants are curling their abdomens to sting. But mostly, the gaster wagging gives the impression of wafting some pheromone for some kind of communication which I am not able to discern (I need ant antennae, I guess.). Perhaps it is like arm or finger wrestling.

I think these situations are more nuanced than just dominance and perhaps many things are still ill defined.

Dr. Trager raised some important concerns about climate specialists and yet we know that climate contributes significantly to  ant occurrence at regional and continental levels. I think Andersen’s work my fit for these larger scales but not so well for more local scales at which I am working. (Scale is a significant concern and challenge in ecological studies. ) I think the scale issue is a part of the local spatial pattern of Comanche as well – it looks like regionally, they are found in sandy soiled prairies associated with oak forest, etc. but locally, Comanche spatial pattern and location may be a matter of queen dispersal. At first perhaps, new queens are attracted to locations with other colonies (conspecific attraction) but after landing, queens have to move farther away.  Later, negative interactions between colonies may come into play as well. Comanche colonies do move — and apparently, not in response to shading, like Pogonomyrmex badius or P. barbatus. But this is just my hunch based on observation and a few preliminary tests.

I also wonder about this: ant species appear to partition habitat seasonally, spatially, and temporarily in terms of activity patterns and so co-exist. These patterns add a level of
complexity which is a challenge.


Alan Andersen and his colleagues have conducted  many studies of ant assemblages with respect to disturbance (mining and deforestation in paricular) and functional groups especially in Australia. An important paper in consideration of these ideas in North America is:

Andersen, A. N. 1997. Functional groups and patterns of organization in North American ant communities: a comparison with Australia. Journal of Biogeography 24 (4): 433-460.

Ant Antennae

I have been thinking about ant antennae for awhile now. First, I became very interested in antennae because there are so many different forms in insects and also in ants. The form of antennae is a key characteristic in ant identification — how are they attached, how long are they, how many segments, is there a club or not, and if there is a club how many segments make up the club?

While the morphology is important to identification, this variety certainly raises functional questions. What are these differences about physiologically? Why are they important and what do they mean behaviorally?

Recently I have been  raising more questions about antennal physiology and sensory perception because of my observations of interactions between individual Comanche harvester ants. I have been conducting nestmate discrimination tests between individual ants by introducing the ants in an arena and observing the ants’ behavior. While these interactions may vary, the antennae almost always have some role. Sometimes, it has been a brief touch or haphazard encounter but other times, the ants spend some seconds or longer facing each other and running their antennae over each other. This may or may not be accompanied by mandible gaping or gaster waging and the encounters may or may not develop. Mostly, the ants go their own way.

It is obvious that the antennae are more than chemosensory or smelling structures and this is well documented in many insects. Antennae may have sensory receptors for mechanical force, tactile stimuli, chemo-sensation, smell/taste, humidity, and air flow.  This multiplicity of perception is a challenge to understand and to place in the context of behavior: what information does an ant get and how does she respond?

Also, the elbow shape of ant antennae make the antennae particularly mobile, rather like our arms. Perhaps, the sensory structure can be thought of, loosely, like our hands and fingers — very sensitive. Although ants don’t use their antennae to manipulate their environment as we use our hands, these structures are key to how the ants interact with their environment. That they have an antenna on each side of the head gives a kind of stereo view of the world — whatever sense they are using. I find this rather fascinating to think about: the stereo world of the ants along all these perceptual lines.

I wonder what these means for the behaviors I am observing. How much are they detecting just being in proximity to one another, how much if they have a bare encounter, and why do some of them spend many seconds using their antennae on one another and others do not? What can they detect, what do they pay attention to, and why are there such differences in responses? Context matters but there is more to this than context.

For the Comanche ant, these questions seem particularly important because they do not use trunk trails and have poor recruitment to resources, etc. which means that pheromones may not be so key to their communication as it is in other ant species. They seem to be rather visual in their orientation for foraging. So what is their perceptual world?  I wonder.