We present the results of a photometric monitoring campaign
for very low mass (VLM) members of the Pleiades. Periodic photometric
variability was detected for nine VLM stars with masses between 0.08
and 0.25 M_sun. These variations are most likely caused by
co-rotating, magnetically induced spots. In comparison with solar-mass
stars, the photometric amplitudes are very low (< 0.04 mag), implying
that either the fraction of the spot-covered area, the asymmetry of the
spot distribution, or the contrast between spots and photospheric
environment decreases with mass. From our lightcurves, there is
evidence for temporal evolution of the spot patterns on timescales
of about two weeks. The rotation periods range from 2.9 h to 40 h and tend to
increase linearly with mass. Compared with more massive stars, we clearly
see a lack of slow rotators among VLM objects. The rotational evolution of
VLM stars is investigated by evolving the previously published periods for
very young objects (Scholz & Eislöffel 2004) forward in time,
and comparing them with those observed here in the Pleiades. We
find that the combination of spin-up by pre-main sequence contraction and
exponential angular momentum loss through stellar winds is able to reproduce
the observed period distribution in the Pleiades. This result may be
explained as a consequence of convective, small-scale magnetic fields.