cantharides

[James di Properzio]

Here's a surprise: while I was surveying usage of "apothecary weight"
(as opp. to "apothecaries' weight"), I happened upon  _Pharmacognosy_ by
H.W. Youngken; Blakiston: Philadelphia,1921, in which I found:

Cantharis U.S.P. (Cantharides)
Synonyms.--Spanish Flies, Russian Flies, etc.

Note the U.S.P (United States Pharmacopoeia) standard drug designation!
There is a page and a half of description of the powdered drug, the
beetle from which it is derived (including a description of its anatomy,
and of the insect's taste), "Production and Commerce," etc., including a
photo of a pile of dead bugs (legend: Spanish Flies (Cantharis
Vesicatoria)).  It claims that they are often found on olive trees in
Spain. Lamentably, uses and dosage are not described.

-James di Properzio