......and the winner is....
The secret to finding the stamp was "earthworm" not "worm"
Because it is widely known, Lumbricus terrestris goes under a variety of common names. In Britain, it is primarily called the Common Earthworm. In North America, the term Nightcrawler (or Vitalis) is also used. In Canada, it is also called the Dew Worm, and in Britain, Lob Worm (though that name is also applied to a marine polychaete). In the rest of the world, most references are just to the scientific name, though, with occasional reference to the above names.
Although this is not the most abundant earthworm, not even in its native range, it is a very conspicuous and familiar earthworm species in garden and agricultural soils of the temperate zone, and is frequently seen on the surface, unlike most other earthworms. It is also used as the example earthworm for millions of biology students around the world, even in areas where the species does not exist.