In addition to this wide selection in insect diversity, several insect species are good representatives for economically important pest insects such as caterpillars, beetles or aphids, while the honeybee belongs to the group of beneficial insects that are essential for pollination. Flies and mosquitoes, on the other hand, are important transmitters of many diseases. Because protein modifications such as glycosylation are not directly encoded by the genomic code, glycosylation in insects was studied at the proteomics level. Recent developments in high-throughput technology for studying proteomes and the public availability of the genome data of different insect species allowed a comparative study of the BAY 43-9006 molecular weight glycoproteins present in the different insect species. Lectin affinity chromatography using the snowdrop lectin was used to selectively purify different sets of mannosylated glycoproteins from different insect species. Subsequently, the purified glycoproteins were identified with LC-MS/MS and characterized according to biological or molecular function. To our knowledge, this is the first report that presents a comparative study of the glycoproteomes present in different insect species. Studying glycoproteomes in different insect species should ultimately result in the development of a more holistic understanding of the importance of glycobiology in insects. One of the major findings in this paper is that very little overlap was observed between the glycoprotein sets derived from the different insect species. This was expected between insect species sampled at different developmental stages because glycosylation profiles change depending on reproductive and developmental stage. However, when comparing only adult insects the diversity in glycoproteins remained extremely high. Since glycosylation is a post-translational modification, changes in carbohydrate composition that were found to be useful during insect evolution can easily be introduced. Because N-glycosylation of proteins occurs in the endoplasmic reticulum and the Golgi apparatus, it was expected that most glycoproteins would be derived from the luminal part of the secretory pathway such as plasma membrane proteins or secreted proteins. Therefore glycoproteins involved in biological processes such as cell adhesion, cell communication and transmembrane transport were expected to be very dominant. Surprisingly, the cumulative percentage of glycoproteins associated with these processes never exceeded more than 12%. Moreover, it is striking that many glycoproteins were related with metabolic processes associated with certain intracellular compartments such as lysosomes. Many lysosomal enzymes are hydrolases such as proteases, lipases or phosphatases which were found to occur very frequently in the different glycoprotein sets. These enzymes are synthesized by membrane-bound ribosomes on the ER and transverse the ER-Golgi pathway to leave the Golgi apparatus in transport vesicles that fuse with lysosomes.