For most, a mosquito bite may seem a very primitive process – a mosquito puts its rigid trunk inside the skin, pumps out blood and flies away. Actually everything is a lot more complex than that. The first thing to note is that only female mosquitoes have special mouthparts to pierce the skin and suck blood, because they need protein from blood to develop their eggs, this is why only female mosquitoes do the biting. All of the organs used for biting, similar as ones used to find a host, are located in the head of a mosquito. Mosquitoes use numerous ways to locate a host, such as sensing carbon dioxide form breath, different body odours, heat and movement with help of antennae and palps. To understand how a mosquito bites, first you must know what mouthparts of a mosquito are included in the biting process.
Mouthparts of a mosquito
When a mosquito is biting our skin, we usually see only one large part that goes inside our skin. This part is called proboscis and it consists of multiple other, smaller mouthparts that each has an important role in the biting process. A mosquito proboscis consists of a labium, labrum, hypopharynx, two mandibles and two maxillae. Mouthparts of a mosquito that goes into the skin are actually not rigid, but very flexible, which you can see in the video below.
- Labium – Labium is an outer sheath that covers other mouthparts, it is not used to puncture the skin and does not go into the skin at all. When a mosquito punctures the skin, labium slides upwards its head and uncovers mandibles and maxillae, which are inserted into the skin.
- Mandibles – A female mosquito has a pair of mandibles, which similar to maxillae are very thin filaments used to pierce the skin. Mandibles have sharp ends to help them go deeper into the flesh.
- Maxillae – A female mosquito has a pair of maxillae, which also are used to pierce the skin, but instead of mandibles, maxillae have toothed blades to better grip the flesh, so other mouthparts can be moved deeper under the skin.
- Hypopharynx – A tube like organ with empty middle, through which a mosquito sends saliva down to a blood vessel.
- Labrum – A tube like organ with empty middle, through which a mosquito pumps blood back up form a blood vessel.
The biting process
Once a female mosquito has located a host, it searches for a place on the skin, where blood vessels are closer to the surface of the skin.
The biting process starts with the outer sheath – labium uncovering two pairs of mandibles and maxillae, which punctures the skin to allow labrum and hypopharynx to go into the flash. When a mosquito has punctured the skin, the mouth parts start to probe around the flash for a blood vessel. Because less than 5 percent of the skin are blood vessels, it may take few tries for a mosquito to successfully locate one. If mosquito does not succeed, it might fly away and search for another place on the skin.
When a blood vessel is located, a mosquito inserts two tube like organs into the vessel – labrum, which is responsible for pumping the blood out of the vessel and hypopharynx, which pumps down saliva. The hypopharynx actually has an important role, because mosquito saliva that is pumped down to the vessel contain substances called anticoagulants, which prevent blood from clotting and allows the mosquito to pump up blood till its abdomen is full, which on average can be around 4 minutes for most mosquito species. A female mosquito will continue to suck blood until the process is disturbed or until it fills its abdomen.
Mosquito saliva remains into the bitten area also after the bite, which causes human immune system to react. The immune system releases a chemical called histamine that enlarges the blood vessels and irritates the nerves around, making the bitten area to swell and cause the itching feeling. Once the immune system breaks down the proteins from saliva, both the swelling and itching dissolve.
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