Flagellated bacteria exhibit a particular mode of locomotion denoted as swarming, where they migrate collective over surfaces and from stable aggregates, which can become highly mobile. Bacteria in swarms are distinctly different from planktonic cells as they assume different morphologies — they are more elongated and the number of flagella is significantly increased — and they are densely packed. This points toward the importance of cell shape and propulsion in swarming. Moreover, collective swarming is observed for other microswimmers, e.g., trypanosomes, which are propelled in a completely different fashion.