Mosquitoes are a common presence in many environments. While both male and female mosquitoes possess a feeding tube, only the female mosquito seeks out blood meals. This behavior is linked to their reproductive cycle, as the proteins in blood are necessary for the development of their eggs. The specialized mouthparts that allow them to feed, often referred to as “needles,” play a role in both nuisance bites and disease transmission.
Anatomy of the Mosquito’s Biting Parts
The mosquito’s “needle” is actually a complex structure called the proboscis, which houses six distinct components known as stylets. The outer sheath of the proboscis is the labium, a scaly, flexible lower lip that encases these delicate stylets when not in use. The labium terminates in two sensory lobes called labella, which help the mosquito locate a suitable biting spot on the skin.
Inside the labium are the fascicle, a bundle of six stylets. The central stylet is the labrum, which is needle-like and serves as the primary food canal for drawing blood. Flanking the labrum are two maxillae, serrated structures designed to saw through the skin, and two mandibles, sharp and helping with initial penetration. The hypopharynx works with the labrum to form a straw-like feeding structure and injects saliva.
The Biting Process
When a female mosquito prepares to feed, she first lands gently on the skin. Using sensory organs on her labella, she probes the skin to find a suitable location, detecting body heat and chemical cues. Once a spot is selected, the outer labium bends back, allowing the fascicle to penetrate the skin.
The maxillae and mandibles work together with a sawing motion to cut through the skin’s surface. The labrum then probes deeper, searching for a blood vessel, guided by receptors that can detect blood. Once a vessel is located and pierced, the gutter-shaped labrum, aided by the hypopharynx, begins to draw blood into the mosquito’s abdomen.
Why the Bite Goes Unnoticed
The initial mosquito bite often goes undetected because of chemical compounds present in the mosquito’s saliva. As the mosquito inserts its proboscis, it injects saliva into the host’s bloodstream. This saliva contains a mix of compounds that facilitate feeding and suppress the host’s immediate response.
Among these compounds are anesthetic agents that numb the area, preventing the host from feeling the initial piercing. The saliva also contains anticoagulants, which prevent the blood from clotting and ensure a continuous flow. These anti-clotting properties allow the mosquito to feed efficiently without interruption.
How Diseases Spread
The hypopharynx plays a direct role in the transmission of pathogens during the biting process. When an infected female mosquito bites, her saliva is injected into the host’s skin. If the mosquito carries viruses, bacteria, or parasites, these pathogens can be present in her saliva.
Upon injection, these infectious agents are introduced into the host’s bloodstream, initiating a new infection. Mosquitoes can acquire these pathogens by feeding on an infected person or animal, with the pathogens replicating within the mosquito’s body before being transmitted to a new host with a subsequent bite. This mechanism makes mosquitoes vectors for diseases such as West Nile virus, Eastern Equine Encephalitis virus, and Jamestown Canyon virus.