Male fleas do bite. Both sexes rely exclusively on host blood for nutrition. Both genders also need blood to mate and reproduce. Fleas imbibe more blood than they can use. The excess blood gets excreted as feces to feed larvae.
Both Sexes are Blood-Feeders
Male and female cat fleas feed exclusively on blood. This trait is unique to fleas and higher flies. In nearly all other blood-feeding arthropods (e.g. ticks, mites, and mosquitoes), blood meals are only taken by females. Fleas are also one of the few insects which rely on blood throughout their entire life cycle, as even larvae consume the blood-laden feces of adults.
Fleas must consume a blood meal before they can mate and lay eggs. Newly emerged females have under-developed ovaries, and feeding triggers sexual maturation. Similarly, the testes of unfed males are blocked by a plug, which prevents sperm transfer. They won’t even attempt to mate. The testicular plug dissolves soon after the first blood meal.
Males Consume less Blood than Females
Adult fleas imbibe and excrete large quantities of blood, especially the females. Male blood meals are shorter and less frequent.
Male fleas feed for an average of 11 minutes, while female feedings last 25 minutes Fig 1. Females can stay attached for over three hours, while males are rarely stationary for more than 20 minutes.
Fig 1 Percent of fleas (y-axis) that completed a blood meal across 80 minutes (x-axis).
Amount of Blood Consumed
During a single meal, males consume less than 15% of the blood which females ingest. In five minutes, females consume twice as much blood. In four hours, females imbibe quadruple the amount of blood of males. Females can imbibe 13.6 uL of blood a day. This is equal to over 15 times their body weight.
Female fleas digest blood faster than males, which suggests differences in physiology. Rapid digestion is more important for females, as blood provides them with the energy and nutrition needed to lay eggs.
Size & Weight
Male fleas are half the size of females. They also have smaller abdomens. Unfed females increase in weight by 140% after a blood meal, while males increase by 19%. Fully fed females weigh 2.5 times more than males.
Excess Blood Consumption & Parental Care
Both genders imbibe more blood than they can use. The extra blood gets excreted as feces (flea dirt). Larvae rely on the fecal blood for food. Male and female feces are equal in protein content. Thus, both genders both provide their offspring with a protein-rich food.
Once feeding begins, imbibing excess blood has few energy costs. However, benefits to the offspring are substantial. Flea dirt can exist in the environment for a long time, serving as nutrients for future generations. Fleas may consume excess blood to harvest out key nutrients found in low levels within blood, such as B vitamins. Regardless, the larvae greatly benefit in the end. It may be an initial evolutionary step towards parental care.