When it comes to summertime pests, mosquitoes are public enemy number one. But why do mosquitoes bite us? Why do their bites itch? And how can you stop mosquitoes from biting you?
For starters, estimates of mosquito species worldwide range from 3,200 to 3,900 or more. More than 150 of those species can be found in the U.S., and 60 of them can be found in North Carolina alone. But they're not all bad guys. Only 10-15 of the species found in North Carolina regularly bite people.
In fact, many mosquitoes pose no threat to humans at all. Specifically, the males. Male mosquitoes feed on nectar and other sources of sugar. Females are the ones you have to worry about.
Why Do Mosquitoes Bite?
While females of some mosquito species do not drink blood, most do. They use the blood to provide the proteins and lipids they need to develop their eggs (which is why males don't bite).
For example, female tiger mosquitoes, or Aedes albopictus, feeds on all kinds of mammals - including humans. This tiger is thought to have come to the U.S. from Japan in the 1980s, and it has made itself at home from Florida to Massachusetts and California. It lays its eggs in water-filled containers near homes or in woodlands, and its eggs are robust enough to survive winter weather. Research from NC State has shown this species is very abundant in neighborhoods with older houses and is a suburban specialist.
Why Do Mosquito Bites Itch?
Mosquitoes are drawn to the carbon dioxide we exhale when we breathe. They land on us and probe our skin, puncturing it with their needle-like mouthparts. This does two things. First, the mouthparts lacerate capillaries in our skin, releasing adenosine triphosphate (ATP) from injured cells. The ATP then stimulates the mosquito's feeding behavior. Second, the mouthparts inject saliva into our blood. The saliva contains a biochemical mixture that prevents the blood from clotting by stopping platelets from sticking together.
The mouthparts damage nerve cells in the skin, causing pain, and the platelets respond to the biochemicals in the saliva by releasing histamines. Those histamines cause additional nerve injury that results in more pain and that annoying itching sensation that accompanies mosquito bites. The swelling associated with mosquito bites stems from the physical tissue damage caused by the mouthparts, and the pooling of blood in the area due to the anticoagulants in the saliva.
Are Mosquito Bites Dangerous?
Mosquitoes are more than just an annoying summer interloper. They are a vector for a host of life-threatening diseases, including malaria and dengue, which claim more than 500,000 lives each year.
Here's an example of how that works. Our friend albopictus is a known vector for Zika fever. When albopictus bites someone infected with Zika fever, it takes in the virus that causes the disease. The virus penetrates the mosquito's midgut during digestion and reproduces in its blood, ultimately colonizing the mosquito's salivary glands. When the mosquito injects its saliva into her next victim, it is unwittingly injecting a fresh batch of Zika virus. Because the saliva prevents the victim's blood from clotting, the virus is able to get into the victim's bloodstream. The virus replicates in the human, causing fever, pain and other symptoms.
How Can I Protect Myself From Mosquito Bites?
The best way to avoid mosquito bites is to eliminate mosquitoes around your house. Because all mosquitoes have to grow up in water (they are aquatic), eliminating standing water near the home can be an effective way of controlling these pests. For example, empty the bird bath regularly, limit items that can collect rainwater, and cover containers.
Another option is to use so-called "mosquito dunks." These donut-shaped disks are available at most hardware stores and are placed in standing water that you can't (or won't) get rid of, such as a rain barrel. Mosquito dunks release a bacterial toxicant that kills mosquito larvae, but won't harm children, pets or even most other insects (such as butterflies or honeybees).
It is also a good idea to use insect repellent when you're spending time outdoors. Contrary to what you may have heard, there are a variety of repellents that work, in addition to DEET. You can find a list of effective repellents here. But, with any of these repellents, you don't want to over-apply - especially with kids. If it's an aerosol spray, spray it onto your hands and then apply it to the skin. And if the repellent isn't working, just put on a little more. Don't douse yourself liberally and keep re-applying. You want just enough to work, not overkill.
If, despite your best efforts, you get some nasty mosquito bites, there are things you can do to minimize your suffering. Put an icepack on the bite, take an oral antihistamine (make sure you take the correct dosage), and put some topical cortisone cream on the bite site to promote healing.
Lastly, if you think that mosquitoes like you more than they like your friends and family - you may be right. Researchers have found that some people are more attractive to mosquitoes than others - though they don't know why. They know it has something to do with the blend of chemicals that we release through our skin, but no one is quite sure what the magic combination is that makes some people irresistible to the little blood suckers. Whatever it is, it's a cologne you don't want.
Note: Many thanks to Michael Reiskind, professor of entomology at NC State, for taking the time to talk to me about mosquitoes. Any errors in the above post are mine alone.
