  The number of long-duration Gamma Ray Burst (LGRB) host galaxies with
measured metallicities and host masses has now grown to over one hundred,
allowing us to investigate how the distributions of both these properties
change with redshift. Using the combined host galaxy metallicity sample from
Graham & Fruchter (2013) and Kr\"uhler et al. (2015), we find a surprising lack
of evolution in the LGRB metallicity distribution across different redshifts.
In particular, the fraction of LGRB hosts with relatively high metallicity
(12+log(O/H) $\geq$ 8.4) remains essentially constant out to z = 2.5. This
result is at odds with the evolution in the mass-metallicity relation of
typical galaxies, which become progressively more metal poor with increasing
redshift. A similar result is found when converting the LGRB host galaxy mass
distribution taken from the SHOALS (Swift GRB Host Galaxy Legacy Survey) sample
to a corresponding metallicity distribution by applying a redshift-dependent
mass-metallicity relation. The SHOALS sample is compiled using an unbiased
selection function implying that the observed lack of evolution in the host
galaxy high metallicity distribution is not caused by selection effects.
However, the LGRB host galaxy metallicities estimated from the stellar mass are
typically a quarter dex higher at all redshifts than the metallicity we measure
spectroscopically. This implies that using mass-metallicity relationships to
estimate host metallicities will thus produce a substantial systematic bias.
