In this paper, we describe the development of a mobile butterfly-watching learning (BWL) system which supports independent learners by offering a new pattern of outdoor mobile learning (or called as m-learning) activities. The proposed BWL system was designed using a wireless mobile ad-hoc learning environment. In our designed system, each individual learner has a wireless handheld device, which is a PDA (Personal Digital Assistant) with an IEEE 802.11 wireless network card and a small-sized CCD camera. One instructor has a notebook computer with a Wi-Fi wireless LAN card which serves as the local server. The notebook has a complete butterfly database. All learners' wireless handheld devices and the notebook constitute a mobile ad-hoc learning environment. During the butterfly-watching activity, each learner takes a distinct butterfly picture, and wirelessly transmits the picture to the local server. A content-based butterfly-image retrieval technique is applied herein to search for the most closely matching butterfly information, which is returned in real time to the learner's wireless handheld device. To illustrate the effect of the BWL system, an outdoor BWL activity was actually performed at elementary school in Taiwan. This article reports on our attempts to develop a new m-learning system to support an independent learning model. We deeply believe that it is worth developing a mobile learning system to provide a possible independent-learning environment for outdoor learners.