Stuart produced a cocktail set with gruesome-looking spiders in 1935 - illustrated in McConnell, Miller's 20th Century Glass, p241. A single glass sold recently on e-bay for £33 (McConnell suggests £350 for the set). And they did produce enamelware in a similar shade of green - eg the flowered pot illustrated in this Cambridge Glass Fair feature: http://www.cambridgeglassfair.com/exhibitions/pastexhibitions/2006-02-stuart.htm
. Their chief designer Ludwig Kny came from a family of Czech glassmakers, which would account for the similarity to Bohemian enamelware.But
all the pieces I've seen have had "Stuart England" etched on the base. And your bugs seem a little more naturalistic and less cartoon-like than the Stuart spiders.
Stop press - just went to search for the spider glass on e-bay and discovered a cocktail shaker in the same pattern, but without the Stuart attribution, which went for only £10.50 - dammit: 160041380023. Note to self: must revise my search terms!