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Mound repair is a long-term modification of soil movements within the mound. Questions abound about this process. What drives it? How is it organized? How does it come to stop? How do termites know when the structure is restored?
This page outlines what is known about how the repair process proceeds, and presents some information on where the soil grains for repair come from. Subsequent pages outline new models for how termites organize themselves into mound repair brigades.
Mound repair is a three-phase process
Soil is mobilized throughout the mound
Soil is translocated to the surface during repair
Mound repair is a three-phase process
Mound repair occurs over a period of many months. It can be broken down into three roughly overlapping phases, which play out over markedly different time and spatial scales.
- An initial recruitment phase that begins immediately upon injury to the mound. This is probably elicited by disturbances to the atmosphere brought about by wind disrupting the atmosphere of the mound and nest. Termites begin to arrive at the site of injury within about five minutes. Recruitment continues over the space of about an hour and merges into the next phase ...
- the stigmergic building phase. Stigmergic building is a self-organizing phenomenon where termites deposit grains of soil into organized structures. You can read more about it below. The stigmergic building phase plays out over roughly a day, and culminated in sealing off the tunnels leading to the site of damage. This marks the onset of the final phase ...
- the remodeling phase. Stigmergic building partly or completely blocks tunnels throughout the mound, which induces its own disruption of air flows within the mound. Over a period of many months, these are removed and tunnels smoothed to their original state. At this point, mound structure is restored to its state prior to the injury.
Stigmergic building is elicited throughout the mound
When a mound is breached, the recruitment phase is followed closely by an extended period of stigmergic building.
Although stigmergic building is most intensely focused at the breach itself, there is nevertheless extensive spots of stigmergic building throughout the mound. This is evident in the photographs to the right. This was a mound damaged by drilling a shallow 10 cm diameter hole into a surface conduit. A day later, the top of the mound above the hole was carefully removed, exposing the network of tunnels within. The top photograph (a) is the cut surface of the mound. I am standing on the cut surface aiming the camera down.
The site of the original injury is located at the top of the photograph, outlined in the red box. Sites of stigmergic building are evident extensively through the mound, outlined in red, even to the side of the mound opposite the hole (just to the left of my foot). Close-ups of several of these sites of stigmergic building are shown in the photographs b-e below.
This extensive distribution of stigmergic building in the mound indicates two important things about the stigmergic building phase.
First, it seems to indicate that stigmergic building is elicited by disturbance to the mound atmosphere, probably through wind energy admitted via the breach. I outline elsewhere a case that stigmergic building is initiated by the chaotic variations of wind energy that are characteristic of turbulent winds. Near the breach, the mound atmosphere is intensely disturbed, and stigmergic building is most intense there. The disturbance extends deeply through the mound's tunnel networks, however, at least initially, so sites of stigmergic building are scattered throughout the mound, as indicated in the cartoon above.
Second, it indicates that stigmergic building is self-sustaining. Once initiated at a location, stigmergic building continues for a time, even when the breach is sealed and the disturbance to the atmosphere removed. TOP
The remodeling phase translocates soil to the mound surface
Once the breach is sealed, the extensive stigmergic building elsewhere in the mound poses obstacles for air flow in tunnels there, and likely poses an ongoing disturbance to the mound atmosphere. This is probably what drives the remodeling phase, which involves clearing the obstacles and moving the soil to the mound surface.
You can see an indication of this in the time-lapse video below. This is an 80-day sequence following the "decapitation" of a mound. You will see that there is considerable movement of soil to the site of injury (the cut top of the mound). On close examination, you will also see that there is considerable remodeling of the mound surface overlaying a surface tunnel that was opened by the decapitation. This indicates an extensive and ongoing movement of soil throughout the mound during the remodeling phase.
The extent of this soil movement can be quantifed by using unexpanded polystyrene (UP) beads as markers for soil transport. Termites will carry these beads as if they are grains of soil. In one experiment, we placed UP beads of four different colors at four locations in a mound, which we subsequently decapitated, as shown in the cartoon to the right. Termites quickly move soil up to the damaged site, as shown in the photograph to the right. Green and blue beads are abundantly evident in the new build, indicating soil was brought to the damaged site from as far as 60 cm away.
This method allowes us to estimate the extent of soil movement within a mound during the remodeling phase. After 90 days, we recovered the repaired cap from the mound. We then recovered beads from the newly-built cap, and counted the number of green beads (placed 30 cm below the cut, blue (placed 60 cm below), red (placed 90 cm below) and yellow beads (placed 120 cm below). This indicates that beads could be drawn from as far away at 120 cm, although the likelihood is small. Ninety percent of beads recovered came from about 65 cm away. TOP
