The effect of tannic acid on gypsy moth,Lymantria dispar(L.), larvae was stadium-specific. First- to third-instar gypsy moth were larger and developed faster on tannin-supplemented artificial diets than on control diets. After the start of the fourth stadium, however, larvae on tannin diets grew more slowly than larvae on control diets. The longer the insect's feeding period after the fourth stadium, the greater the negative effect of the tannin diets on eventual pupal weights. Female gypsy moths were most affected by tannin content of the diet because their extra instar results in a longer feeding period. This results in a proportionally greater influence of the negative effects of tannins.