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It has long been thought that the life cycle of Streptomyces bacteria encompasses three developmental stages: vegetative hyphae, aerial hyphae and spores. Here, we show interactions between Streptomyces and fungi trigger a previously unobserved mode of Streptomyces development. We term these Streptomyces cells ‘explorers’, for their ability to adopt a non-branching vegetative hyphal conformation and rapidly transverse solid surfaces. Fungi trigger Streptomyces exploratory growth in part by altering the composition of the growth medium, and Streptomyces explorer cells can communicate this exploratory behaviour to other physically separated streptomycetes using an airborne volatile organic compound (VOC). These results reveal that interkingdom interactions can trigger novel developmental behaviours in bacteria, here, causing Streptomyces to deviate from its classically-defined life cycle. Furthermore, this work provides evidence that VOCs can act as long-range communication signals capable of propagating microbial morphological switches. DOI: http://dx.doi.org/10.7554/eLife.21738.001, eLife digest Soil is home to many bacteria. In fact, soil gets it characteristic ‘earthy’ smell from a common type of soil bacteria known as Streptomyces. Remarkably, Streptomyces are also the original sources of most of the antibiotics that are prescribed by doctors to treat bacterial infections. Scientists have been studying Streptomyces for over 70 years, and in all this time, there has been unanimous agreement on how these bacteria grow. That is to say that, unlike most other bacteria, Streptomyces grow like plants: they don’t move, and instead produce spores that are dispersed like seeds. This stationary lifestyle makes these bacteria somewhat vulnerable to predators, and so it is thought that Streptomyces make antibiotics to help protect themselves from other bacteria that are able to move around in the soil. However, this established view of Streptomyces growth has now been turned on its head because Jones et al. have discovered that Streptomyces bacteria can indeed move when grown in the presence of fungi. Specifically, when a species of Streptomyces is grown with yeast, some of the bacteria start to explore their environment, move over top of other bacteria and up hard surfaces to heights that would be the equivalent of humans scaling Mount Everest. Unexpectedly, Jones et al. also found that these “explorer” Steptomyces can communicate with nearby Streptomyces bacteria with a perfume-like airborne signal and convince their relatives to begin exploring too. Furthermore, while this volatile signal promotes the growth of Streptomyces, it adversely affects other bacteria and makes them sicker such that they are less able to grow and survive. Together these findings reveal new ways that bacteria and other microbes can interact and communicate with each other. They also emphasise that researchers will need to consider such long-range communication strategies if they hope to better understand microbial communities. DOI: http://dx.doi.org/10.7554/eLife.21738.002