The use of sensor networks in sophisticated applications is emerging as a new trend. However, the integration and coordination of heterogeneous sensors is still a challenge, especially when the target application scenario is susceptible to constant changes. Such systems must adapt themselves in order to fulfill requirements that can also change during the system runtime. Moreover, the changes that occur in such scenarios require services located at different places during the system runtime. Due to the dynamicity of this context, system adaptations must take place very quickly, requiring that decisions for adaptation are taken autonomously by the system without waiting for human operator's directions. Thus a reflective behavior must be provided. This paper presents a reflective middleware that supports reflective behaviors to address adaptation needs of heterogeneous sensor networks deployed in dynamic scenarios. This middleware presents specific handling of concerns related to real-time, service adaptation and resource allocation through network reasoning. These concerns are addressed mainly by the use of mobile and multi-agents, and aspect-oriented concepts. The use of multi-agents represents the spreading of intelligence over the network, while the mobile-agents provide service adaptation by code mobility. In the same direction, aspects address behavioral adaptations related to crosscutting concerns.