The Skinny on No-See-Ums

Categories: News

There is a mosquito wreaking havoc in the tropical areas of Southern Mexico and Central America—as well as other tropical locations. The scientific name for this tiny mosquito is Ceratopogonidae, but they are better know as “no-see-ums,” deriving the name from the fact that they are hard to see. In fact, one traveler says, “they are no bigger than a period, and appear as tiny black dots.” With a surprisingly painful bite, these little critters deserve attention. Unfortunately, it seems the only remedy comes with the use of chemicals and repellents.

Every year, we get reports from Undercurrent subscribers about how swarms of no-see-ums hampered shore diving, cut beachside bar time short, and left them with a vacation souvenir of nasty bites, bumps and welts. In some cases, reactions to the bites have kept divers out of the water.

The Bay Islands in Honduras are the worst. John and Marilyn Walker (Castro Valley, CA) were there last May, staying at Fantasy Island, and were frequently bit, even indoors. “The island in general features many biting insects, but even though we sprayed with DEET and slept with the air conditioner on, we still got red, itchy welts,” they wrote.

Christopher Mohr (Dublin, OH), who also stayed at Fantasy Island, was amazed how intense and determined they were in their hunt for human blood. “They were bad unless you covered yourself with insect repellant. The bites were still on us almost a week after we returned home. The resort was diligent in spraying, which helped, but these insects are worth paying attention to -- they can be a problem.”

They’re a problem nearly everywhere in the Caribbean, and I can attest to that. While lying on a beach in the Bahamas, I got 147 bites, which ruined a day of diving. On the Honduran island of Guanaja, they chewed me up again, leaving 60 marks on me while I waited for a 7:30 a.m. flight. Regardless of where you are in the Caribbean, chances are you’ll get a few bites.

The no-see-um obviously gets its name because it is nearly invisible, small enough to go through window screens. The ones coming at me on the Utila beach were little black dots the size of a period, flying down at me like a miniature fleet of Luftwaffe. The scientific name for the no-see-um isCeratopogonidae, but it has accumulated more common names, including sand flea, sand fly, biting midge and punky. They’re common to wet areas like beaches, wetlands and creeks. Divers will experience them at their worst in Honduras, Nicaragua, Belize and Mexico’s southern coasts. Many resorts spray their grounds but can’t get them all – besides the Fantasy Island reports we mentioned above, Belize’s Isla Marisol resort is also a big breeding ground. And of course like any blight, no-see-ums breed like crazy. They lay eggs in standing water, where larvae hatch and feed on dead vegetation. Within just a few days, the larva becomes a pupa, then an adult that leaves the nest in search of food.

Though one-third the size of a mosquito, its bite is inversely more painful. While mosquito bites cause raised lumps on the skin that become very itchy, they can be soothed with calomine lotion, Benadryl, or aloe vera. No-seeum bites result in typically a whole bunch of red welts that irritate the skin, are slow to deflate, and cause three to four days of severe itching. No-see-ums on the beach will bite most often on the ankles and lower legs, just because they’re closer to the ground. But if you’re unlucky enough to pass through a dark swarm of them, no part of your body is off limits and they could fly into your eyes, ears, nose or mouth.

Every person reacts differently to no-see-um bites. Two people may receive an equal number of bites, and one will not be affected while the other will turn into a walking pincushion. For divers who suffer allergic reactions, one treatment of antihistamines may work for one person, while another may need a bigger, stronger dose of something more potent.

Bigger Than Its Bite

At times, a no-see-um bite can lead to something far worse than a red welt and uncomfortable dive days. A few years ago, we reported the story of Undercurrent readers Barry Lipman and Ingrid Preuss and their no-see-umplagued visit to Guanaja. The bugs ruined a beach picnic when Lipman received several hundred bites and had to flee the beach. That night, he developed a 102-degree fever and discovered that he was covered with little itching bumps. A six-day course of prednisone alleviated his symptoms and allowed him to continue diving, but Preuss was not as lucky. Four months after the trip, she developed small, reddish blemishes on her face at the locations of some no-see-um bites. A dermatologist diagnosed it as cystic acne, but the blemishes grew into ulcerated lesions. It took Preuss a trip to Curaçao to visit specialists in order to get an accurate diagnosis: leishmaniasis.

Not every type of no-see-um carries the disease. Scientists have found the culprits to be no-see-ums of the genuses Phlebotomus, typically found in Asia and Africa, and Lutzomya, found in Latin America and the Caribbean. Like mosquitoes, gestating female no-see-ums hungry for protein search for a “blood meal,” and in the process can transmit one of the twenty-plus species of protozoan parasites responsible for the disease. Lipman was told that the fever and rash he developed in Guanaja the night after receiving hundreds of no-see-um bites were not the result of leishmaniasis but a reaction to the toxins he received from the bites themselves. Multiple no-see-um bites can also cause death by kidney failure from their toxins alone, without any other infectious agent involved.

While leishmaniasis affects 12 million people in 88 countries (with two million new infections annually), most of the high-risk areas are not dive destinations. However, leishmaniasis is well-entrenched in Mexico, Honduras, Belize and other parts of Central America. It also appears to be spreading to some islands in the Caribbean, including Trinidad and Hispaniola. Elsewhere, Thailand and Egypt have also reported cases.

Though leishmaniasis accounts for less than five percent of the tropical infections American travelers return with each year, unless the victim consults a physician specializing in tropical medicine, diagnosis is often inaccurate. The disease itself is difficult to cure and victims are prone to recurrences. For decades antimony (sodium stibogluconate) has been considered the most effective treatment, but the three-week intravenous regimen is toxic in itself, and the parasite is reportedly becoming resistant in some areas. Other treatments are available but no cure is 100 percent effective, and there are currently no preventative medications or vaccines.

Signs of leishmaniasis are sores that change in size and appearance over time. They often end up looking somewhat like a volcano, with a raised edge and central crater. Some sores are covered by a scab and can be painless or painful. Some people also have swollen glands near the sores (for example, under the arm if the sores are on the arm or hand). If you fear persistent sores are signaling leishmaniasis, ask for a referral to a tropical medicine specialist or contact the U.S. Centers for Disease Control (, which can help clinicians with biopsies and cultures, and recommend and provide medication.

You Can’t Beat DEET

Fortunately, the chances are slim that you’ll die from a nosee- um bite, but if you are a person who experiences strong reactions to bee stings or mosquito bites, chances are you’ll also react strongly to these.

The first line of defense is dousing yourself with insect repellents containing at least 30 percent DEET. Some divers report success with cactus juice, a repellant sold in Roatan that comes in a brown bottle and smells like Citronella or Avon’s Skin-So-Soft, although Consumer Reports recently found the latter offered no protection at all against the aedes mosquito, an aggressive species that can carry dengue fever. Most likely, the people who found these questionable remedies helpful wouldn’t be prone to attacks anyhow.

A more aggressive measure is applying concentrated doses of DEET. Generally, the higher concentration of the chemical DEET, the more effective the repellent. Consumer Reports’ top-rated Deep Woods Off with 98 percent DEET kept the aedes away for 12 hours. Products with 30 to 34 percent DEET protected for at least five hours, while those with seven percent DEET lasted only an hour against the aedes.

The CDC recently recommended two other active ingredients to fight bites. One is picardin, which is odorless and non-greasy.Consumer Reports recommends Cutter Advanced, which prevents bites for two to three hours for aggressive species, eight hours for less so. Another is oil of lemon eucalyptus, which the CDC says is as effective as DEET. Consumer Reports tested Repel Lemon Eucalyptus spray against another repellent containing 10 percent DEET and found that Repel prevented bites for four to seven hours for aggressive mosquito species, and more than 12 hours for less aggressive mosquitoes, longer than the DEET repellant and picardin.

DEET Plus Sunscreen a No-No

While it’s safe to apply it regularly over a two-week vacation, don’t use it with sunscreen. Recent studies using animal and human skin cells suggest the mixture might increase DEET absorption but might not make sunscreen not protect as well. About 20 versions of sunscreen-bug repellent combinations are sold, but because the Food and Drug Administration regulates sunscreen and the Environmental Protection Agency regulates insect repellant, guidance for using these combo products is in limbo since they don’t really belong to either agency. Complicating the issue, Canadian researchers recently tested human skin cells and found questions beyond the all-in-one products: Spraying on DEET and then rubbing on sunscreen actually increased DEET absorption the most.

Be alert when you’re sitting at the outdoors bar for your post-dive drinks – no-see-ums wake up when the sun goes down and are most active at dawn and dusk. If possible, wear long-sleeved shirts, long pants and socks. Make them lightcolored and avoid dark or bright colors. Thoroughly spraying clothing and fine-mesh screens and bed nets with permethrin will give added protection (also dry them thoroughly before use). Aerosol insecticides can also be used in rooms to clear them of pests.

The most effective way to fend off no-see-ums is to take a liveaboard trip, but the odds of bringing home anything worse than itchy welts are too small to require a change of dive travel plans. Still, it makes sense to take aggressive steps to avoid becoming the main course for these biting bugs.

via UnderCurrent

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