  We present an analysis of long-term photometric variability for nearby red
dwarfs at optical wavelengths. The sample consists of 264 M dwarfs south of DEC
= +30 with V-K = 3.96-9.16 and Mv~10-20 (spectral types M2V-M8V), most of which
are within 25 pc. The stars have been observed in the VRI filters for ~4-14
years at the CTIO/SMARTS 0.9m telescope. Of the 238 red dwarfs within 25 pc, we
find that only ~8% are photometrically variable by at least 20 mmag (~2%) in
the VRI bands. We find that high variability at optical wavelengths over the
long-term can be used to identify young stars. Overall, however, the fluxes of
most red dwarfs at optical wavelengths are steady to a few percent over the
long term. The low overall rate of photometric variability for red dwarfs is
consistent with results found in previous work on similar stars on shorter
timescales, with the body of work indicating that most red dwarfs are only
mildly variable. We highlight 17 stars that show long-term changes in
brightness, sometimes because of flaring activity or spots, and sometimes
because of stellar cycles similar to our Sun's solar cycle. Remarkably, two
targets show brightnesses that monotonically increase (G 169-029) or decrease
(WT 460AB) by several percent over a decade. We also provide long-term
variability measurements for seven M dwarfs within 25 pc that host exoplanets,
none of which vary by more than 20 mmag. Both as a population, and for the
specific red dwarfs with exoplanets observed here, photometric variability is
therefore often not a concern for planetary environments, at least at the
optical wavelengths where they emit much of their light.
