Macro-programming advocates the use of high-level abstractions to specify distributed systems as a whole. However, macro-programming implementations are often centralised. In this paper we present PICO-MP, the first fully decentralised macro-programming middleware for wireless sensor and actuator network (WSAN) applications. PICO-MP incorporates a novel publish-subscribe service that can correlate events scattered across a WSAN using global formulae specifications that are automatically checked in a distributed fashion. PICO-MP has been implemented for the TinyOS operating system and validated on a case study that uses global formulae to improve energy efficiency (lifetime) of the implementation.