Despite attempts in a number of studies to utilize muscle tissue and cells as microactuators, all of the biohybrid microdevices have been operable only in the culture medium and none have worked in air due to the dry environment. This paper demonstrates an atmospheric-operable bioactuator (AOB) fabricated by packaging an insect dorsal vessel (DV) tissue with a small amount of culture medium inside a capsule. The AOB, consisting of microtweezers and the capsule, was designed based on a structural simulation that took into account the capillary effect. The base part of the microtweezers was deformed by spontaneous contractions of the DV tissue in the medium inside the capsule, by which the front edges of the microtweezer arms projecting above the medium surface were also deformed. First, we confirmed in the medium that the DV tissue was able to reduce the gap between the arm tips of the microtweezers. After taking the AOB out of the medium, as we expected, the AOB continued to work in air at room temperature. The gap reduction in air became larger than the one in the medium due to a surface tension effect, which was consistent with the simulation findings on the surface tension by the phase-field method. Second, we demonstrated that the AOB deformed a thin-wall ring placed between its tips in air. Third, we measured the lifetime of the AOB. The AOB kept working for around 40 minutes in air, but eventually stopped due to medium evaporation. As the evaporation progressed, the microtweezers were pressed onto the capsule wall by the surface tension and opening and closing stopped. Finally, we attempted to prevent the medium from evaporating by pouring liquid paraffin (l-paraffin) over the medium after lipophilic coating of the capsule. As a result, we succeeded in prolonging the AOB lifetime to more than five days. In this study, we demonstrated the significant potential of insect muscle tissue and cells as a bioactuator in air and at room temperature. By integrating insect tissue and cells not only into a microspace but also onto a substrate, we expect to realize a biohybrid MEMS device with various functions in the near future.