Cat flea. Coloured scanning electron micrograph (SEM) of a cat flea (Ctenocephalides felis). Its body is laterally-flattened to allow it to move easily through the fur of its cat host. The flea's antennae can be withdrawn into its head. Comb-like spines on the head, called ctenidia, help to anchor the flea in the fur of its host. The mandibles are modified to pierce the skin and suck blood. Fleas have three pairs of legs, with the long hindlegs adapted for jumping. Most fleas remain on their host only while feeding. Magnification unknown.