From a glossary of the Cornish dialect:
Bilders. Heradlum spJioncUlmm. Cut as fodder for
pigs. Couch (Hist, of Polperro) thinks that this
name, in other parts of Cornwall, is applied to the
poisonous hemlock, water-drop-wort. JEnanihe.
Note that the above appears to be a misspelling or a typo for heracleum sphondylium, which is known as common hogweed; see here for more info:
http://en.wikipedia.org/wiki/Common_Hogweed