How do fleas bite and feed?

Summary

Flea mouth parts are specialized for blood feeding. The main structure is composed of 3 needle-like stylets. The two outer stylets pierce a host’s skin, while the central stylet enters a capillary to draw blood. While imbibing blood, salivary ducts open to introduce anticoagulant saliva to the wound.

Details

Fleas are Parasites

Obligatory Parasites

Cat fleas are obligatory parasites. Both sexes rely exclusively on host blood for sustenance. This trait is unique to fleas and the higher flies. Blood meals are taken only by females in most species of blood-feeding arthropods. Fleas are also one of the few insects which rely on blood throughout their entire life cycle. The larvae consume the blood-laden feces from adults.

Sedentary Ectoparasites

Fleas live on their host, not inside their body. As such, they’re classified as ectoparasites. To feed, mouth parts are inserted into the host’s skin, while the body remains motionless on the surface. Thus, fleas are classified as sedentary parasites. Fleas don’t attach onto hosts like ticks. Instead, fleas are covered spines, bristles, and combs which help prevent removal from host hair. The spination also keeps their heads wedged against host skin during feeding.

Vessel Feeding

Cat fleas are vessel (capillary) feeders, as opposed to pool feeders. The host’s blood pressure gets exploited by the parasite, resulting in a rapid feeding. Vessel feeding is the more advantageous strategy, as faster blood meals leave fleas vulnerable for shorter periods of time.

Flea Mouth Parts

Fleas mouth parts are well-adapted for piercing host skin and imbibing blood. In addition, fleas have strong nearby sucking (buccal and pharyngeal) muscles. The mouth points downward in an arrow-like shape.

• Labrum: “Upper lip” structure of insects.
• Labium: “Lower lip” structure of insects.
• Labial palps: Pair of long, five-segmented sensory organs which come from the labium.
• Maxillae: Pair of short, wide plates located in front the labial palps. Also called lobes or stipes.
• Maxillary palps: A long, four-segmented palpus comes off each maxilla.
• Fascicle: Combination of 3 long, slender stylets which are supported within the labial palps.
• Maxillary lacinae: Outer 2 stylets of the fascicle. They’re serrated and blade-like.
• Median epipharynx: Central stylet of the fascicle. It joins with the maxillae to form a tube-like food canal.

How Fleas Feed

Exploratory Probing

Once on a host, fleas seek out a suitable bite location with their labial palps. Next, exploratory probing is done, where skin is pierced to find a blood vessel. Anticoagulant saliva is introduced to the wound, which helps locate blood. Probing alone causes a bite reaction. As a result, fleas bites often appear as clusters of lesions.

Piercing Skin & Drawing Blood

The fascicle is used to pierce the host’s skin. The sharp maxillary laciniae easily puncture the epidermis. The tip of the median epipharynx then enters into a blood vessel, and blood begins flowing up the food canal. Muscles located along the foregut contract, creating suction and causing a pumping action. Blood flows into the esophagus, and then into the midgut to be digested.

Introducing Saliva

Four pear-shaped salivary glands are located within a flea’s abdomen. The glands connect to the mouth with long ducts. As blood is imbibed, a salivary canal is formed by the almost-touching maxillary lacinae, which remain outside the wound. The glands open and large droplets of saliva fall onto tissue surrounding the bite.

The saliva’s anticoagulant proprietaries help fleas imbibe blood. There’s also a substance in the saliva that spreads and softens the dermal tissue, which makes it easier to insert and remove the fascicle. When the meal is over, the mouth parts are rapidly withdrawn. Remarkably little damage occurs at the bite location. The hemorrhage will be slight or absent.

Disruptions during Feeding

Fleas often get disturbed while feeding. Movement from the host, or the host’s clothing, can cause fleas to abandon a blood meal. They then relocate and bite again nearby. This causes multiple bites marks in the same neighborhood.

Feeding Duration

Cat fleas begin feeding within a few minutes of acquiring a host. Many bite within 30 seconds. They’re able to feed to repletion in 10 minutes. On average, females feed for 25 minutes, and males for 11 minutes. Females imbibe over twice as much blood as males.

Digestion

After blood is imbibed, a structure in the gut called the proventricular armature acts as a valve to prevent regurgitation. It also releases components needed for digestion. The digestive enzymes of fleas are specially adapted for handling blood. Digestion occurs in a sac-like midgut, which empties into a short hindgut, which in-turn ends at the anus.

There are believed to be gender differences in digestion physiology, as female fleas process blood faster than males. It’s important for females to digest blood rapidly, as they need the nutrition and energy for egg laying.

Feces Excretion

Adult fleas imbibe much more blood than they can use. As blood rapidly passes through the gut, only that nearest to the functional midcut cells is retained for digestion. As a result, fleas produce large amounts of feces, consisting largely of undigested blood. Adult feces (flea dirt) is the primary food source of flea larvae.

References