Newly discovered Mesozoic fleas have been recently reported from the Middle Jurassic Daohugou fauna (ca. 165 Ma) and the Early Cretaceous Jehol fauna (ca. 125 Ma) of Northeast China. These giant fleas are represented by three forms each with both with males and females. The females are slightly to distinctly larger than the males. These ancient ectoparasites display some general habitus, such as large size (more than 2 cm long in some specimens), more or less dorso-ventrally flattened body, and non-jumping hind legs. Their developed, posteriorly-directed setae on thorax and abdomen and scattered ctenidia on legs indicate an ectoparasitical behavior that lived on haired or feathered vertebrates. Most modern fleas parasitize mammals, and small, advanced groups (about 5%) parasitize birds. The possible Mesozoic hosts of these fossil fleas include dinosaurs and pterosaurs with hair-like feathers, early birds, and early mammals. This primary study indicates clear morphological differences between these Mesozoic fleas. At least three different groups may be distinguished. These are: 1) the Middle Jurassic types (Middle Jurassic to Early Cretaceous, China), armed with a typical long and serrate piercing-suctorial siphon like some Recent groups (e.g. Tungidae); 2) Tarwinia-type (Early Cretaceous, China and Australia), armed with a relatively simple siphon and different tarsal structures; 3) Saurophthirus-type (Early Cretaceous, Russia and China), armed with a relatively simple siphon and very slender and elongate legs. The basal morphological differences probably indicate a remarkable adaptability to different hosts.

Strashila is the most bizarre animal among all known fossil insects. It was hypothesized to be an ectoparasite, even a supposed dinosaur parasite. The new morphological details indicate it is a true aquatic insect. Moreover, Saurodectes vrsanskyi from Siberia was suggested to have louse affinities, but it is more likely a wingless dipteran.