## 2 Experiment setup  
As shown in Fig.1, a small isolated room measuring about 2\(\times\)2\(\times\)2 m\({}^{3}\) was used as the experimental chamber. A small space heater was used to regulate the ambient temperature to 26-28 \({}^{\circ}\)C, which was monitored by using a remote wireless thermometer from outside of the chamber. As a play stage for fire ants, a plastic tub measuring 350\(\times\)190\(\times\)120 mm\({}^{3}\) was placed in an aluminum support frame, confining the perimeter of the base of the tub but allowing for general deformation of the bottom surface of the tub. The 120-mm sides of the tub were coated with Fluon(r) AD1 to prevent the ants from escaping. The 350\(\times\)190 mm\({}^{2}\) inner bottom of the tub was painted with grid lines of distance of 31.75 mm (1 \(\mathrm{\SIUnitSymbol4}\) inches) for vibration mode analysis and image calibration. Since the vibratory sensory organs of fire ants appear to be most sensitive to the acceleration of the substrate vibration [15], 12 accelerometers were attached to the outer bottom surface of the tub to monitor the vibration. The tub support frame was connected to the center insert of a shaker by a steel rod. The shaker was placed on a vibration absorbent pad in order to minimize the effects of ambient seismic energy. Four small halogen lamps served as light sources for imaging purposes, and they were placed to prevent shadows. A 10-bit CMOS digital camera with 17-\(\mathrm{\SIUnitSymbolMicro m}\) pixels was attached to a tripod and fixed to a working distance of 600-mm to capture images of the fire ants before and after excitation. The CMOS camera has a memory big enough to save more than 1,200 frames in each of 10 separate zones, so that image groups of multiple tests can be acquired without pausing for data downloading. The camera acquired image  
Figure 1: Schematic illustration of experiment setup for fire ant tracking. frames of 1024\(\times\)512 pixels at a frame rate of 60 fps, which covered an area of 418\(\times\)209 mm\({}^{2}\) in the objective plane with an imaging scale of 2.45 pixel/mm. The exposure time of 1/500 second allowed for sharp images of moving ants. Other equipment components were placed outside of the room to minimize human interferences with fire ant behavior. The shaker was driven by the output of a power amplifier, and the vibration signals acquired at the tub bottom were amplified using low-noise amplifiers and processed using a dynamic signal analyzer. A computer was used to control the image acquisition and to download images after a test case was completed. Image processing and evaluation were completed offline. 200 workers of fire ants were collected and put into the tub for each test case. Acclimation to the new environment was allowed for 24 hours prior to commencement of experimentation, with drip irrigation providing a source of moisture. Lighting inside the chamber room was regulated by turning the lights on at \(\sim\) 8:00 AM every morning and then turning them off at \(\sim\) 5:00 PM to simulate the daylight cycle. According to previous tests [16], the exciting frequency was selected to be 466 Hz to effectively stimulate the fire ants distributed on the tub bottom. Several groups of image frames were recorded for each test case: the first ant image recording group was taken one minute before the excitation as a reference. The second ant image recording group was acquired a few seconds after the ants were excited. The remaining 8 ant image recording groups were obtained at different time delays to observe the development of the ant motion within a one-hour period. Each image group has 1228 frames that were acquired at a rate of 60 fps in about 20 seconds. A sample image is shown in Fig.2. In this sample image, most of the ants cluster on the lower left corner of the image frame; some of the ants randomly distribute on the tub bottom; and a food source of two _Heliothis virescens_ pupae is placed on the mid-high right.