What do fleas look like and how do they bite humans? - briefly
Fleas are tiny, laterally flattened insects measuring 1–3 mm, dark reddish‑brown, with powerful hind legs that enable rapid jumps. They penetrate human skin with a needle‑like proboscis, inject anticoagulant saliva, and consume blood, producing a small, itchy bite spot.
What do fleas look like and how do they bite humans? - in detail
Fleas are small, laterally compressed insects measuring 1–4 mm in length. Their bodies exhibit a dark reddish‑brown coloration that may vary from tan to black depending on species and engorgement. The head is reduced, bearing large compound eyes and short antennae concealed in grooves. Three pairs of legs emerge from the thorax; the hind legs are markedly enlarged, ending in a row of spines that enable rapid jumps of up to 150 times the body length. The abdomen consists of segmented segments covered by tiny bristles (setae) that assist in detecting vibrations and temperature changes.
Key morphological traits:
- Lateral flattening facilitates movement through host fur or hair.
- Strong, spring‑loaded hind femora generate jumping force.
- Serrated, piercing‑sucking mouthparts (the proboscis) consist of a sheath, a stylet bundle, and a salivary canal.
- Specialized tarsal pads increase grip on host surfaces.
Host detection relies on a combination of sensory cues. Fleas sense carbon dioxide exhaled by mammals, detect body heat through thermoreceptors, and respond to vibrations and odors emitted by skin. Upon contact, the insect climbs the host’s hair or clothing, positioning its mouthparts toward the skin.
The biting process begins when the proboscis penetrates the epidermis. The stylets separate to create a narrow channel, while the salivary canal injects a mixture of anticoagulant proteins and enzymes. These substances prevent blood clotting and suppress local inflammation, allowing continuous ingestion of blood. Blood is drawn up the salivary canal by a muscular pump within the flea’s head, then transferred to the digestive tract.
Human bites appear as small, red papules often grouped in clusters. Initial irritation may be mild; however, the anticoagulant proteins can provoke allergic reactions, leading to itching, swelling, or secondary infection if the lesions are scratched. Flea saliva may also transmit pathogens such as Yersinia pestis (plague) or Rickettsia spp., though transmission to humans is comparatively rare.