The cap mesenchyme is essential for ureteric branching during mammalian kidney development, but the mechanism by which the cap domains are maintained at the tips of the epithelial ureteric tree is not clear. Now, using ex vivo timelapse imaging, Combes et al. show that the cells of the cap mesenchyme are highly motile. As well as migrating within and between cap domains, these cells attach and detach from the ureteric epithelium over time. The researchers suggest that this swarming behaviour enables a distinct cap mesenchyme domain to be maintained whilst also facilitating dynamic remodelling in response to changes in the tip.