Earlier work showed the existence of sialic acid (SA) in the prothoracic glands (PGs) ofGalleria mellonella(Karaçali et al., 1997). In this paper we investigated the role of SA during the degeneration process of PGs. Neuraminidase-digested larval PGs were incubated within the hemolymph collected from same age larvae. Light and electron microscopic observations showed incomplete capsule formation by the accumulation of hemocytes around desialylated gland cells, but not in the control group. Desialylated larval PG cells were recognized as a foreign structure or non-self by hemocytes. The result indicates that SA acts as a mask for hemocytic receptors during the larval period under normal conditions. However, in the absence of SA, the glands start to degenerate. We provide an explanation for the role of SA in the recognition process of hemocytes that initiates the degeneration of PGs in pupal cells and show the functionality of SA in insects, confirming that SA is a universal molecule.