Adult fleas are small, wingless insects that feed on the blood of mammals and birds, making them common parasites. Their coloration provides a first clue to their identity, though their appearance shifts depending on recent activities. Understanding the changes in a flea’s color provides insight into its feeding habits and helps identify a potential infestation.
The Definitive Color of an Adult Flea
The typical adult flea, such as the common cat flea (Ctenocephalides felis), ranges in color from dark brown to a warm reddish-brown. This dark, mahogany coloring allows them to remain camouflaged within the dense fur or hair of a host. Their exoskeleton often possesses a glossy sheen, sometimes making them appear nearly black from a distance.
Adult fleas measure about 1/8 of an inch (2.5 to 4 millimeters) in length. Their bodies are distinctive, being laterally compressed, meaning they are narrow from side to side. This streamlined, flat shape enables them to move quickly through the thick coat of a host.
How Feeding Status Changes Appearance
A flea’s appearance changes notably after it has consumed a meal. When unfed, its abdomen is relatively flat and the segments overlap closely, contributing to a dark brown or blackish appearance. Unfed fleas are sometimes a lighter reddish-brown overall.
After an adult flea takes a blood meal, its abdomen expands dramatically to accommodate the ingested blood, sometimes nearly doubling in size. This engorgement stretches the abdominal segments, and the presence of digested blood gives the flea a plumper, darker, and more reddish-black appearance. The darker coloration is a direct result of the host’s blood filling the digestive tract, which is visible through the outer shell.
Visual Clues for Confirming an Infestation
Live fleas can be seen, especially around the neck, base of the tail, and inner thighs, but their rapid movement makes them difficult to spot. A more consistent indicator of an infestation is “flea dirt,” the common term for flea feces. Flea dirt looks like tiny specks of black pepper or small, dark grains of sand scattered in the host’s fur or bedding.
Flea dirt is composed of the host’s dried, undigested blood, excreted by the adult fleas. To confirm if the specks are flea dirt and not environmental debris, perform the “wet paper towel test.” By collecting the specks onto a damp white paper towel, the dried blood within the feces will rehydrate, confirming an active flea population if the specks smear into a reddish-brown or rusty color.