Results of previous field excavation of nest structure of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), the Formosan subterranean termite, indicated that the total length of the gallery system ranged up to 580 m, and its total space may occupy >34,800 cm³. Because Formosan subterranean termite does not build mounds, it has been speculated that it creates tunnel space by compacting soil. The objective of this study is to test a “modified soil-compaction hypothesis” that Formosan subterranean termite removed and compacted soil to increase space during tunnel excavation. Contrary to the hypothesis, the deposited sand was less dense than the unexcavated sand in all replications; thus, we rejected the soil-compaction hypothesis. Instead, we offered wood-consumption hypothesis that termites gain the tunnel space as a result of consuming wood. When termites were placed with wood pieces for 30 d, the decreased volume of consumed wood was significantly higher than the increased volume of carton material. The net increased space is ≈50% of volume of consumed wood. We speculate that the space created by wood consumption could be transformed into tunnel space during soil displacement.