long range order in 2D [@Toner1995; @Toner1998], anomalous fluctuations [@Ramaswamy2003; @Narayan2007], dynamical structures and patterns [@Koch1994; @Budrene1991; @Budrene1995; @Matsushita1997]. In addition to serving as prototypical systems to explore emergent dynamical behavior, active materials also form the physical scaffold of biological systems in that active matter, when coupled to regulatory signaling pathways, provides a model for a variety of living systems, such as bacterial biofilms or the cytoskeleton of a cell.

Active particles are generally elongated and form orientationally ordered states [@Ramaswamy2010]. The nature of the ordered state depends on both the symmetry of the individual particles and the symmetry of the aligning interactions (see Fig. \[Fig1\]). Physical realizations of *polar* active particles (characterized by a head and a tail) include bacteria, asymmetric vibrated granular rods, and polarized migrating cells. Polar active entities are often modeled as self-propelled (SP) particles, where the activity is incorporated via a self-propulsion velocity of the individual entities. *Apolar* (head-tail symmetric) active particles, often referred to as “shakers”, have also been considered in the literature. Realizations are symmetric vibrated rods [@Narayan2007]. It has also been argued that melanocytes, the cell that distribute pigments in our skins, may effectively behave as “shakers” [@Gruler1999; @Kemkemer2000].

The nature of 