  We study the dynamics of self-propelled chains with the excluded volume
interaction via the Brownian dynamics simulation, in which the bending
elasticity of chains is varied. The changes of the bending elasticity lead to
various characteristics of the clustering behavior in the short-chain-only
system. When a long self-propelled chain is mixed with these short chains, it
can fold into the spiral-coil, a steadily rotating spiral conformation, either
at a high density of short chains or at a low density if the long chain itself
is sufficiently flexible. Our results qualitatively support the speculation on
that the formation of the spiral-coil in the swarm of Vibrio alginolyticus is
triggered by collisions from the clusters of the shorter bacteria.
