Neutrophil swarming is a type of coordinated neutrophil movement that acts in response to acute tissue inflammation or infection. The term comes from the swarming characteristics of insects that are similar to the behavior of neutrophils in response to an infection. These processes have mostly been studied in tissues of mice and studies of mouse ear tissue has proved to be very effective at observing neutrophil movement. Neutrophil swarming typically aggregates at surface layers of tissue so the thin nature of the mouse ear tissue makes for a good model to study this process. Additionally, zebrafish larvae have been used for the study of neutrophil movement mainly because of their translucence during the first few days of their development. With transgenic lines that fluorescently label zebrafish neutrophils, the cells can be tracked by epifluorescence or confocal microscopy during the course of an inflammatory response. Through this method, specific subpopulations of neutrophils can be tracked and their origin and fate during the induction and resolution of inflammation is observed. Another advantage for using zebrafish to study neutrophil swarming is that adaptive immunity for this organism does not develop until around 4 weeks of age. This allows for the study of neutrophil movement and other host immune responses independent of adaptive immune responses. Variations A study of the lymph nodes of mice that were infected by injection of parasites into their earflaps revealed two types of neutrophil swarming: transient and persistent swarms. Transient swarms are characterized by groups of 10-150 neutrophils forming multiple small cell clusters within 10-40 minutes that quickly dispersed. Persistent swarms showed clusters of more than 300 neutrophils and recruitment lasted for more than 40 minutes. For both the transient and persistent swarms, the formed neutrophil clusters appeared to be competing with each other with the larger clusters attracting neutrophils from the smaller clusters. The study also revealed two distinct phases in swarm formation. The first phase occurs when a small number of “pioneer” neutrophils respond to an initial signal and form small clusters and this is followed by the second phase where there are a large scale migration of neutrophils leading to the growth of multiple cell clusters. The exact size or duration of swarms depends on the specific inflammatory conditions as well as the tissue type of the infection location. Several factors that influence the swarm phenotype are: the size of the initial tissue damage, the presence