This chapter discusses hemolymph, which is the circulating fluid or “blood” of insects. Insect hemolymph differs substantially from vertebrate blood, with the absence of erythrocytes and a high concentration of free amino acids being two of the common distinguishing features. Themain component of hemolymph is water, which functions as a solvent for a variety of molecules. Water in hemolymph makes up to 20–50% of the total water in insect bodies, with larval stages generally having a larger relative hemolymph volume than adults. Hemolymph serves as a water storage pool for use by tissues during desiccation and as a storage depot for other types of chemicals. It also contains circulating cells called hemocytes. Hemolymph can function as a hydraulic fluid, for example, in the expansion of a newly molted butterfly's wings and serves important roles in the immune system and in transport of hormones, nutrients, and metabolites.
