Fleas are wingless insects with a laterally compressed body of about 1.5-4 mm length. Like all insects they possess six legs and three body segments. Taxonomically they belong to the order Siphonaptera (Eckert et al. 2000) (Table 1). This family contains several species and subspecies.

Fleas represent one of the most important external parasites (Mehlhorn 2000; Mehlhorn et al. 2001b). At the moment there are more than 2000 described species and subspecies throughout the world (Borror et al. 1981).

These species belong to the families Pulicidae, including Pulex spp., Ctenocephalides spp., Spilopsyllus spp. and Archaeopsyllus spp., or the familia Ceratophyllidae with the genuses Ceratophyllus or Nosopsyllus to mention only some of the most important veterinary and human representatives.

Fleas have a history of about 60 million years and were already found on prehistoric mammals. While becoming parasitic the original exterior of the two-wing insects, also designated as the order Diptera, has changed by losing the wings in the adults, whereas the larval form still has similarity with the larva of the order Diptera (Strenger 1973). About 95% of the ~2000 different flea species parasitize on mammals, 5% live on birds.

Table 1. Taxonomy of fleas

• Borror DJ, DeLong DW, Triplehorn CA (eds) (1981) Order Siphonaptera. In: An introduction to the study of insects, 5th edn. WB Saunders Co, Philadelphia, pp 620-628
• Eckert J, Rommel M, Kutzer E (2000) Erreger von Parasitosen: Systematik, Taxonomie und allgemeine Merkmale. In: Rommel M, Eckert J, Kutzer E, Körting W, Schnieder T (eds) Veterinärmedizinische Parasitologie, 5th edn. Parey Verlag, Berlin, pp 2-39
• Mehlhorn H (2000) Mode of action of imidacloprid and comparison with other insecticides (i.e. fipronil and selamectin) during in vivo and in vitro experiments. Suppl Comp Cont Educ Pract Vet 22 (4A):4-8
• Mehlhorn H, Hansen O, Mencke N (2001b) Comparative study on the effects of three insecticides (fipronil, imidacloprid, selamectin) on the developmental stages of the cat flea (Ctenocephalides felis Bouché 1835): a light and electron microscopic analysis of in vivo and in vitro experiments. Parasitol Res (in press)
• Strenger A (1973) Zur Ernährungsbiologie der Larve von Ctenocephalides felis felis. B. Zool Jahrb Syst Bd 100:64-80