Cecropins are antimicrobial peptides.They were first isolated from the hemolymph of Hyalophora cecropia, from whence the term cecropin was derived. Cecropins lyse bacterial cell membranes; they also inhibit proline uptake and cause leaky membranes. Cecropins constitute a main part of the cell-free immunity of insects. Cecropins are small proteins of about 31 - 37 amino acid residues active against both Gram-positive and Gram-negative bacteria. Cecropins isolated from insects other than Hyalophora cecropia (Cecropia moth) have been given various names; bactericidin, lepidopteran, sarcotoxin, etc. All of these peptides are structurally related. Cecropin P1, an intestinal antibacterial peptide from Sus scrofa (Pig), also belongs to this family. Cecropin family also consists Cecropin A and Cecropin B.