Priobium sp., an anobiid beetle, can attack wood used for historic constructions in Japan. Its life history and feeding biology, especially larval development and behavior, are poorly understood because the beetles are hidden inside wood most of the time. We used X-ray computed tomography (CT) to regularly scan wood blocks infested with the larvae of the Priobium sp. and observed the process of their movement and development inside. The wood blocks were scanned at intervals of approximately 10 days from July 2019, and the analysis was based on the CT data until February 2020. The CT images clearly captured the silhouettes of the larvae, as well as parts of wood and frass. By registering the CT volume data obtained on different scanning dates, the movement of individual larvae could be traced. The larvae, in most cases, seemed to move about within the frass packed inside the wood blocks, instead of newly tunneling into undamaged parts of the blocks. By measuring the position coordinates of the larvae, their displacement in the scanning intervals was quantified. The larvae became inactive when the temperature dropped to around 10 °C. The body length of the larvae kept fluctuating, but no apparent growth was observed throughout the experiment.

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