Full-field 2-D projection images created using phase-contrast synchrotron x-rays. Images were chosen to highlight the highest quality imagery currently obtainable (a, b) and corresponding stills from live video (c-l). (a) Carabid beetle (Pterostichus stygicus) in dorsoventral view with legs removed and sacrificed prior to imaging. Image is a high-resolution composite of multiple images. The air-filled tubes of the tracheal system can be prominently seen. The dark spots on the left side, mid-body are soil particles on the outer surface of the elytra. (b) Close-in view of one section of the prothorax, showing the branching pattern of tracheae. (c, d) One half-cycle of rhythmic tracheal collapse in a live carabid beetle (Platynus decentis) in dorsoventral view. Images are frame grabs from a video recording (See Additional file 1); time interval is 0.5 s. Total time of collapse and reinflation of the tubes is 1.0 s. (e-l) Visualization of internal food movement using labeled markers. (e) Schematic of the head and thorax of a butterfly (Pieris rapae) in lateral view. The foregut is shown in red; the square highlights the region of video stills in (f-h), and black arrow indicates the direction of food movement. (f-h) Video stills of passage of a food bolus posteriorly through the esophagus, moving through the frame from upper right to lower left (see Additional file 2). Red arrows indicate the leading (f) and trailing (h) edges of the bolus. Interval between frames is 0.5 s. Food is sugar water/iodine mixture. X-ray energy (33.2 keV) was tuned to just above the K-edge absorption band for iodine. (i) Schematic of a carabid beetle (Pterostichus stygicus) in dorsoventral view (legs removed). Circular structures in mid-body represent coxae; the gut is represented in gray and red. Square highlights video in (j-l), visualization of cadmium-laced food in the foregut (see additional file 3). Video stills (j-l) show movement of gut including anterior-posterior translation and squeezing of the crop (cr) and translation and rotation of the proventriculus (pr). The proventriculus is a valve that leads to the midgut ; here, it is closed. Note that only parts of the gut with contrast agent can be seen. Interval between frames: j-k, 2 s; k-l, 6 s. X-ray energy, 25 keV. Scale bars: a,b, 1 mm; c,d, 200 μm; f-h, 200 μm; j-l, 1 mm.