  Based on a microscopic model, we develop a continuum description for a
suspension of microscopic self propelled particles. With this continuum
description we study the role of long-range interactions in destabilizing
macroscopic ordered phases that are developed by short-range interactions.
Long-wavelength fluctuations can destabilize both isotropic and also symmetry
broken polar phase in a suspension of dipolar particles. The instabilities in a
suspension of pullers (pushers) arise from splay (bend) fluctuations. Such
instabilities are not seen in a suspension of quadrupolar particles.

Statistical Mechanics;Soft Condensed Matter