The diameters of the tracheal trunks which supply air to the foregut (oesophagus and crop diverticulum) were measured in 26 European chrysopid species representing 10 genera. Marked differences between the genera were observed and, in several species, between the sexes. Females have larger tracheae, especially to the  crop. Only in Chrysopa species (except Chrysopa viridana), do males and females have relatively small tracheal trunks and an approximately similar relative air supply.
The size of the mandibles was measured in 19 species and, in most of them, the crop and gut content were analysed. Only the adult of the genus Chrysopa are true predators with strong mandibles.
The species of the other genera have significantly larger tracheae and small mandibles; their crops harbour yeast symbiotes, and they are honeydew feeders. However, Hypochrysa elegans has almost no ventilation to the foregut, and no symbiotes; it has strong mandibles and is an exclusive pollen feeder.