Following the 2009 Churchill Cup van der Merwe joined Glasgow Warriors on a two-year contract. Van der Merwe debuted for the Scottish side as a replacement against the Cardiff Blues in October of that year. During the 2009–10 Celtic League season van der Merwe made 11 appearances scoring 4 tries in the process for a total of 20 points as well as playing in 4 matches of the 2009–10 Heineken Cup.