They Call it “Sea Lice”

I have played in the waters of the northern Gulf of Mexico all of my life… but I have never heard of this – “sea lice.” It has been in the news recently and I have had a couple inquiries concerning it so I decided to investigate.


A few weeks ago there was a report of “sea lice” in Walton County. Bathers were leaving the water with a terrible skin condition that was itchy and painful, particularly in areas beneath their bathing suits. Photos of this show a series of whelps over the area – almost like a rash. What was causing it? And what can you do about it?

this illustration the anatomy of the thimble jellyfish - believed to be the creature known as "sea lice".   Graphic: University of Michigan
this illustration the anatomy of the thimble jellyfish – believed to be the creature known as “sea lice”.
Graphic: University of Michigan

My first stop was Dr. Chris Pomory, an invertebrate zoologist at the University of West Florida. Dr. Pomory indicated that the culprit was most probably the larva of a small medusa jellyfish called the thimble jellyfish (Linuche unguiculata), though he included that it could be caused by the larva any of the smaller medusa. Dr. Maia McGuire, Florida Sea Grant, told me a colleague of hers was working on this issue when she was in grad school at the University of Miami. Published in 1994, it too pointed the finger at the larva of the thimble jellyfish. Here I found the term “Sea Bathers Eruption” (SBE) associated with occurrences of this. I also found another report of SBE from Brazil in 2012 – once again pointing the finger at the thimble jellyfish larva. So there you go… the most probable cause is the larva of the thimble jellyfish. Note here though… Dr. McGuire indicated that SBE was something that was problematic in south Florida and the Caribbean… reports from the northern Gulf are not common.


So what is this “thimble jellyfish”?

Most know what a jellyfish is but many may not know there are two body forms (polyp and medusa) and may not know about their life cycles. The classic jellyfish is what we call a medusa. These typically have a bell shaped body and, undulating this bell, swim through the water dragging their nematocyst-loaded tentacles searching for food. Nematocysts are small cells that contain an extendable dart with a drop of venom – this is what causes the sting. Nematocysts are released by a triggering mechanism which is stimulated either by pressure (touch) or particular chemicals in the water column – hence the jellyfish cannot actually fire it themselves. The thimble jellyfish are dioecious, meaning there are male and females, and the fertilized eggs of the mating pair are released into the ocean. These young develop into a larva called planula, and these seem to be the source of the problem. Drifting in the water column they become entrapped between your skin and your bathing suit where the pressure of the suit against the skin, especially after leaving the water, causes the nematocyst to fire and wham – you are stung… multiple times. The planula larva are more common near the surface so swimmers and snorkelers seem to have more problems with them.


So what can be done if you encounter them?

Well – there are two schools of thought on this. (1), go ahead and stimulate the release of all nematocysts on your body and get it over with or (2) do everything you can to keep any more nematocysts from “firing”. Some prefer #1 – they will use sand and rub over the area where the jellyfish larva are. This will trigger the release of any unfired nematocyst, you will deal with the pain, and it will be over. However, you should be aware that many humans have a strong reaction to jellyfish stings and that firing more nematocysts may not be in your best interest. Some will want to take a freshwater shower to rinse them off. This too will trigger any unfired nematocysts and you will be stung yet again. Using vinegar will have the same response as freshwater.

So what do you if you DO NOT to get stung more? Well… the correct answer is to get the bathing suit off and rinse in seawater that DOES NOT contain the larva… easier said than done – but is the best bet.


Is there any relief for the pain and itch?

Dr. McGuire provided the following:

Once sea bather’s eruption occurs (and you have taken off your swimsuit and showered), an application of diluted vinegar or rubbing alcohol may neutralize any toxin left on the skin. An ice pack may help to relieve any pain. The most useful treatment is 1% hydrocortisone lotion applied 2-3 times a day for 1-2 weeks. Topical calamine lotion with 1% menthol may also be soothing. Nonsteroidal anti-inflammatory drugs such as ibuprofen and aspirin (but not in children) may also help to reduce pain and inflammation. If the reaction is severe, the injured person may suffer from headache, fever, chills, weakness, vomiting, itchy eyes and burning on urination, and should be treated with oral prednisone (steroids). The stinging cells may remain in the bathing suit even after it dries, so once a person has developed sea bather’s eruption, the clothing should undergo machine washing or be thoroughly rinsed in alcohol or vinegar, then be washed by hand with soap and water. Antihistamines may also be of some benefit. Other treatments that have been suggested include remedies made with sodium bicarbonate, sugar, urine, olive oil, and meat tenderizer although some of these some may increase the release of toxin and aggravate the rash. Symptoms of malaise, tummy upsets and fever should be treated in the normal fashion.


This is a “new kid on the block” for those of us in the northern Gulf. It has been in south Florida and the Caribbean for a few decades. As the Gulf warms, more outbreaks may occur, there is really not much to be done about that. Hopefully most reactions will be minor, as with any other jellyfish sting.


Posted: June 10, 2016

Category: Coasts & Marine, Natural Resources, Wildlife
Tags: Sea Lice, Sea Life, Thimble Jellyfish

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