Lionel with a sea urchin in foot in Koh Rong, Cambodia
Lionel checking out the sea urchin's prickly spines!

If you have ever ventured out into the ocean as a surfer, swimmer, or scuba diver, you have likely come across one of the many interesting species of sea urchins. You can find a wide variety of sea urchins in different colors, shapes, and sizes. If you don’t bother them, they won’t bother you; but step on one and get a sea urchin in your foot, and you will definitely need to know what to do to treat the injury!

Let’s learn more about what to do with a sea urchin sting and more about this prickly creature!

Prickly Creatures

Seemingly harmless, the sea urchin has a unique defense system that includes two different modes of protection. This protection comes most obviously in the form of the exterior spikes, which may contain harmful venom. The urchins commonly use their spikes to defend themselves against predators such as other fish, eels, and crabs. 

This article will help you discover how best to remove the sea urchin’s spines with our five-step method. For example, you may get one of the spines of a sea urchin in your foot for the first time; what will you do? Safely removing the sea urchin from your skin is something that every beachgoer should know how to do just in case you suffer from an unexpected sting. Keep reading as we answer some of the most commonly asked questions about sea urchin stings and removing the spines of a sea urchin from your foot. 

What is a Sea Urchin?

A sea urchin is a type of marine animal known as an echinoderm. Each of the 950 or more urchins species plays a vital role in maintaining the reef’s ecosystem. Numerous benefits are linked to urchins’ presence, such as how they work to balance coral and algae, build reef resilience, and provide settlement spaces for corals. In contrast, a large sea urchin outbreak could lead to unsustainable bio-erosion.

How Big is a Sea Urchin?

The sea urchin’s average size is one to four inches (10.1 centimeters), while larger species can reach up to 14 inches (35.5 centimeters). Long-Spined Urchin (Diadema Antillarum) quickly penetrates the skin with their spines if you contact one in the water. 

How Does a Sea Urchin Travel in the Water? 

A sea urchin moves around by using its tube feet which are assisted by its spines. Don’t worry; they typically only move about 3 to 20 inches (50.8 centimeters) per day. The sea urchin can not intentionally reach out towards you and bite or sting you; it simply can be a matter of being in the wrong place at the wrong time.

Where does a Sea Urchin Live? 

You can only find sea urchins in the ocean, and they can not survive in freshwater systems. The urchins enjoy living in rock pools, coral reefs, and seagrass beds. They move in a similar way to starfish, and while they don’t have eyes, they can sense movement. 

Are Sea Urchins Poisonous?

The dangerous Flower Urchin / Toxopneustes pileolus
A close-up of the beautiful but dangerous flower sea urchin (Toxopneustes Pileolus). Photo by Vincent C. Chen

One sea urchin species called the Flower Sea Urchin or Toxopneustes Pileolus is the most dangerous sea urchin in the world. It is commonly found in the tropical Indo-West Pacific which includes the Indian Ocean, the western and central Pacific Ocean, connecting together in the general area of Indonesia. Other sea urchins with poisonous spines include those in the Echinothuridae, Toxopneustes, and Tripneustes species. 

Are Sea Urchins Deadly? 

Fatalities from sea urchin stings have occurred and some sea urchin species (as noted above) can be deadly. In severe cases, nausea, vomiting, paresthesias (“pins and needles”), muscular paralysis, and respiratory distress may occur. 

Sea urchins are also harvested and consumed as a delicacy in some locations around the world; commercial fishing and harvesting are considered a high-risk industry. Fishermen are more likely to suffer injury as they intentionally come into contact with the sea urchins.

Want to read about our own experience of ‘catching’ and eating sea urchins in Cambodia?  

Sea Urchin Spines

Sea urchin spines are composed of calcium carbonate and are currently the only animals that can still see without having eyes. This is truly amazing as they instinctively use the cells in their feet to sense light.

Prickly sea urchin
Despite its appearance, this is not the sea urchin’s ‘eye.’ Their spines are light sensitive and this is how they ‘see.’ Photo Gerhard G. / Pixabay

How Can I Avoid a Sea Urchin Sting? 

To avoid touching a sea urchin, mind your step, and avoid jumping into the shallow water from the shore or a boat if you do not have a clear view of the bottom.

For scuba divers, the tides and currents can cause you to brush up against the urchins, and yes, the spines can even puncture through neoprene so take good care to avoid them as much as possible. It is common for new scuba divers to be directed to kneel on the sandy floor-bed when practicing Open Water skills, so do exercise caution and always check where you are placing your legs and arms.

Read More: The Difference between a Scuba Diver vs Open Water Certification

What Happens when I Step on a Sea Urchin?

In the best case scenario of stepping on a sea urchin, the delicate spine will just break off and be embedded in your skin. It will be sensitive but not toxic. To encourage the spine to come out, you can soak your foot in clean, warm water. This will soften your skin and over time your body will push the non-toxic spine out.

However, multiple deep puncture wounds from stepping on a sea urchin may cause severe injury, especially if accompanied by symptoms such as:

  • Weakness
  • Muscle aches
  • Shock
  • Paralysis
  • Intense fatigue

A serious sea urchin sting may cause pain to the injury site leading to swelling and inflammation. Symptoms from a venomous sea urchin sting will lead to additional symptoms such as dizziness, breathing problems, chest pain, changes in heart rate, loss of consciousness, nausea, and vomiting. In the worst-case scenario, the venom will enter the bloodstream and cause death. 

Sea Urchin Removal

If you have a sea urchin spine injury, it is essential to remove the affected area’s spine. The calcium-filled spines that a sting can leave behind can be difficult to remove from the skin, so if you can, ask someone for assistance and be gentle to avoid the spines from breaking inside the skin. 

Anyone with allergic reactions to bites or stings should take extra precautions and get medical assistance immediately. The following is a guide to help you known what steps to take if this should occur and is not intended to replace the possible need for medical care: 

Step 1: Immerse the area for 30 – 90 minutes in hot water. Sea urchin toxins are heat-labile meaning hot water immersion is very effective in reducing the pain. If you can not access hot water, try to source vinegar as this will help the spines dissolve, making them easier to remove. Vinegar and hot water bath commonly use treatment to break down the spines so they can be successfully removed from the skin.

Step 2: Remove the larger spines with tweezers (use a magnifying glass if possible). 

Step 3: Remove the smaller spines known as pedicellariae by scraping them carefully with a razor or a credit card.

Step 4: Clean the wound with warm water and soap. Always use the cleanest possible water to prevent infection to the wound.

Step 5: Rinse the wound with clean water again to ensure all spines are removed. If you find that the spines can not be removed, you should see medical attention for assistance right away. 

It is typical for the site of the sting to turn blue or black. This is a symptom of the dye, which the sea urchin may release on impact or as a result of minor bruising. Remember to keep the wound clean and treat the area with a topical antiseptic ointment to ensure no bacteria causes an infection. If you are concerned about infection, seek further medical advice as a doctor may suggest a round of antibiotics.

Final Thoughts 

Sea urchins should not bother you while you are exploring the ocean’s beauty, but it is possible that a simple misstep can lead you to be stung and get the sea urchin spines in your foot. Follow the five steps for removing the sea urchin spines from your foot mentioned above and seek further medical attention if required. We hope that the sea urchin populations continue to protect the coral reefs and learn to appreciate their vital role in the ecosystem.