S-trifluorobutenyl thiocarbonic acid esters of the formula STR1 and salts thereof, wherein X is R1 N or S and Y is RS or R3 R2 N; wherein R is a metal or a radical selected from alkyl, cycloalkylalkyl, halocycloalkylalkyl, alkenyl, haloalkyl, haloalkenyl, alkynyl, alkoxyalkyl, alkylthioalkyl, alkoxycarbonylalkyl, halophenoxyalkyl, trialkylsilylalkyl, (vinyl)dialkylsilylalkyl, (allyl)dialkylsilylalkyl, 2-chlorothiophene-5-ylmethyl, phenylalkyl, halophenylalkyl, nitrophenylalkyl, haloalkylphenylalkyl, dialkyl-2,3-dihydrobenzofuran-7-yl, [2-methyl-(1,1'-biphenyl)-3-yl]methyl, 3-phenoxybenzyl, phenylthioalkyl, halophenylthioalkyl, dialkylphosphoryl, dialkylthiophosphoryl, dialkylisoxazolylalkyl and thienylisoxazolylalkyl; wherein R1 is alkyl, cycloalkyl, cyano, dialkyl-2,3-dihydrobenzofuran-7-yl, halophenyl, halophenylalkyl, haloalkoxyphenyl, pyridinyl, halopyridinyl, alkyl-1,3,4-thiadiazolyl, haloalkyl-1,3,4-thiadiazolyl, benzothiazolyl, dialkyloxazolyl or thiazolinyl; wherein R2 is hydrogen or alkyl; and wherein R3 is alkyl, haloalkyl, cycloalkyl, cycloalkylalkyl, dialkylaminoalkyl, dialkyl-2-oxazolyl, 2-thiazolinyl, 2-benzothiazolyl, 4-phenyl-2-thiazolyl, alkyl-1,3,4-thiadiazolyl, haloalkyl-1,3,4-thiadiazolyl, pyridinyl, halopyridinyl, phenyl, halophenyl, halophenylalkyl, haloalkoxyphenyl, or dialkyl-2,3-dihydrobenzofuran-7-yl; provided that: when X is S, Y is R3 R2 N, when X is R1 N, Y is RS, R1 is other than alkyl and R is other than haloalkenyl; and when X is R1 N where R1 is CN and Y is RS, R is other than alkali metal. The compounds exhibit nematicidal and anthelmintic activity and are useful in agriculture and veterinary practice.