  We combine a semi-analytical model of galaxy formation with a very large
simulation which follows the growth of large scale structure in a LambdaCDM
universe to predict the clustering of Ly-alpha emitters. We find that the
clustering strength of Ly-alpha emitters has only a weak dependence on Ly-alpha
luminosity but a strong dependence on redshift. With increasing redshift,
Ly-alpha emitters trace progressively rarer, higher density regions of the
universe. Due to the large volume of the simulation, over 100 times bigger than
any previously used for this application, we can construct mock catalogues of
Ly-alpha emitters and study the sample variance of current and forthcoming
surveys. We find that the number and clustering of Ly-alpha emitters in our
mock catalogues are in agreement with measurements from current surveys, but
that there is a considerable scatter in these quantities. We argue that a
proposed survey of emitters at z=8.8 should be extended significantly in solid
angle to allow a robust measurement of Ly-alpha emitter clustering.
