The parasitic Hymenoptera are an extremely diverse group of insects comprising over 100,000 species and the largest group of parasitic animals. Their behavior and ecology have been extensively investigated as a result of the group's importance to biological control and pest management. Lipoidal compounds play important roles in the physiology and metabolism of insects and other arthropods. The major lipid fractions of both arthropods and "higher" animals are glycerides and phospholipids. Glycerides or acylglycerols, esters of long chain fatty acids and glycerol, are the major components of depot or storage fat, and triglyceride comprises the bulk of this neutral lipid fraction with partial glyceride generally present in very small amounts. In contrast to the maintenance of the fatty acid composition of most animals within rather specific limits, G. K. Bracken and J. S. Barlow reported that the fatty acid composition of the total body fats in the ichneumonid parasite, Exeristes comstockii, was nearly identical to that of its host species.