Bees use thorax vibration to achieve flight, facilitate pollination, and communicate information. When threatened, many bee species buzz to warn predators of an impending sting; this behavior is referred to as defensive buzzing. Force production and thoracic vibrations have been evaluated during flight, but little is known about defensive buzzing. We measured the directional force production and thoracic vibration velocity during defensive buzzing. We mounted carpenter bees Xylocopa californica to a carbon fiber post fixed to a high-sensitivity transducer to measure force production. Thorax vibration velocity was measured via laser vibrometry. Root-mean-squared (RMS) force production was 25.86 ± 9.6 mN along the dorsal-ventral axis, 15.37 ± 6.6 mN along the anterior-posterior axis, and 8.72 ± 3.1 mN along the medial-lateral axis. This suggests the bee is vibrating with axes aligned with its indirect flight muscles. RMS thorax velocity was 20.86 ± 6.5 mm/s and occurred at a fundamental frequency of 95.9 ± 19.4 Hz. Individual bees adjusted their primary thorax vibration frequency approximately 15% from the average. Because force components exhibit pronounced integer harmonics of the primary thorax vibration frequency, bees can excite a wide frequency range of nearly 500 Hz. This ability may be useful during behaviors such as buzz pollination, where the insect may benefit from resonating a flowers’ pored anther. This work suggests that the dynamics of the bee’s thorax differ between defensive buzzes and other behaviors.