Microscopy was performed using either a Leica SP5 point scanning confocal (63×/1.4 HCX PL Apo CS oil lens) or an Andor Dragonfly Spinning Disk confocal microscope (60× water objective). Images were collected with LAS AF or the Andor Fusion software respectively. Minor processing (Gaussian blur) was performed using FIJI. For live imaging, embryos undergoing germband extension were mounted ventro‐laterally between O2‐permeable membrane (Sartorius) and a glass coverslip in Voltalef oil (Attachem). Embryos were gently squashed such that the ventrolateral ectoderm was flattened.