Cat flea head (Ctenocephalides felis). Its body is laterally-flattened to allow it to move easily through the fur of its cat host. Comb-like spines on the head, called ctenidia, help to anchor the flea in the fur of its host. Fleas have three pairs of legs, with the long hind legs adapted for jumping. Most fleas remain on their host only while feeding. Magnification unknown.