Fig. 1.

Experimental apparatus. (A) Top-down view of the arena with backlit panorama. The thermal barrier is depicted in red. (B) A schematic side view of the fly visualization setup. Near-IR LEDs (light-emitting diodes) mounted with the camera above the arena, and two of the eight halogen lights arranged in a circular array are depicted. (C) A schematic vertical cross section of Arena 1 with passive cooling. Recirculating hot water heats the thermal barrier and four CPU fans cool the walking platform (only one is depicted). (D) A schematic vertical cross section of Arena 2 with active cooling. The thermal barrier is a strip of galvanized steel wrapped in a rope heater and insulated from the walking platform by a layer of neoprene. The walking platform in actively cooled by a PID-controlled array of four thermoelectric modules with water-cooled heat sinks (only one is depicted). (E) The two arrangements of cones in the arena. The arena floor is shown in grey for illustration purposes only; the floor and cones were both painted matte black. (F) The color-code convention used for the cones of equal lateral surface area. The angle between the base and lateral surface, and the height, are noted below each cone.