In this study we hypothesized that Grammostola rosea Walckenaer 1837, an active predator of large size that depends on its two paired book lungs for respiration, would have a refined low energy strategy based on its thin air-hemolymph barrier. The morphology of book lungs and the oxygen consumption at 20° and 30° C under normal and starvation conditions were studied. The oxygen consumption was low compared to that expected for spiders from the allometric relationship, 0.027 ± 0.01 ml O₂ g⁻¹ h⁻¹ (average ± standard deviation), and it was depressed at 30° C under starvation. The harmonic mean thickness of the air-hemolymph barrier was 0.14 ± 0.03 µm, the respiratory surface density was 122.99 ± 35.84 mm⁻¹, and the book lung volume ranged from 12.2 to 37.5 mm³. With these parameters a high oxygen diffusion capacity was estimated. The combination of low resting oxygen consumption and high pulmonary oxygen conductance results in very low gradients of partial oxygen pressures across the air-hemolymph barrier (0.12–0.16 kPa) required to satisfy the resting oxygen demands.