Files in this Data Supplement:

• Supplemental Figure S1 -

  Fig. S1. Trial in which specimen (mass 189.0 mg) appeared to be using rhythmic tracheal compressions, but stopped when the x-ray beam was turned on. The beetle resumed compressions when the beam was turned off (not shown).

• Movie 1 -

  Movie 1. Rhythmic tracheal compression in the anterior head of the carabid beetle Pterostichus stygicus. Note occurrence of tracheal collapse in the mandibles as well. Anterior is to the left; field of view is 3.2 mm×2.4 mm. Frame rate, 15 frames s⁻¹.

• Movie 2 -

  Movie 2. Rhythmic tracheal compression in the prothorax of the carabid beetle Pterostichus stygicus. Anterior is to the left; field of view is 3.2 mm×2.4 mm. Frame rate, 15 frames s⁻¹.

• Movie 3 -

  Movie 3. Rhythmic tracheal compression in the mesothorax of the carabid beetle Pterostichus stygicus. Circular structures are coxae. Anterior is to the left; field of view is 3.2 mm×2.4 mm. Frame rate, 15 frames s⁻¹.

• Movie 4 -

  Movie 4. Rhythmic tracheal compression in the lateral mesothorax and metathorax of the carabid beetle Pterostichus stygicus. Anterior is to the left; field of view is 3.2mm×2.4 mm. Frame rate, 15 frames s⁻¹.

• Movie 5 -

  Movie 5. Rhythmic tracheal compression in the abdomen of the carabid beetle Pterostichus stygicus. Anterior is to the left; field of view is 3.2 mm×2.4 mm. Frame rate, 15 frames s⁻¹.

• Movie 6 -

  Movie 6. Correlation of tracheal compressions with pulses of external CO₂ in the carabid beetle Pterostichus stygicus. Video is focused on the prothorax and femur of the beetle. Anterior is to the left; field of view is 3.2 mm×2.4 mm. Frame rate, 15 frames s⁻¹.