Cecropins [PMID: 3318666, PMID: 2015623, PMID: 1915368] are potent antibacterial proteins that constitute a main part of the cell-free immunity of insects. Cecropins are small proteins of about 35 amino acid residues active against both Gram-positive and Gram-negative bacteria. They seem to exert a lytic action on bacterial membranes. 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.