There is provided a method or improving the surface sterility of an invertebrate organism having an external cuticle, comprising contacting an outer surface of the organism, or a portion thereof, with an aqueous alcohol solution of less than about 70% v/v for a period of less than 60 seconds. The method is especially useful to provide research-grade organisms which can be utilised in research involving injection of compositions through the external cuticle, by reducing phenotype changes resulting from introduction of surface contaminants into the interior of the organism.