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Wildlife guide · Mustang Island

Jellyfish in Port Aransas.

Most of the gelatinous creatures in the Gulf off Mustang Island are harmless — moon jellies and cabbage-head (cannonball) jellies rarely sting. The one to learn to recognize is the Portuguese man o' war, with its blue-purple gas-filled sail. Here's what you'll see, when stings are most likely, and the right first aid if it happens.

Jellyfish (and look-alikes like the Portuguese man o' war) are a normal part of life on the Texas Gulf. Stings happen, but serious medical incidents are rare. The single most useful skill is recognizing a man o' war — alive in the water or washed up on the wet sand — and giving it room. The purple beach flag means dangerous marine life has been reported on the beach; check it before you swim.

Species you'll see on this coast

Moon jellyfish

Aurelia aurita

The classic translucent saucer shape with four pale-pink horseshoe markings. Mild sting that's often barely noticeable. Common year-round but most visible in summer. Largely harmless.

Cabbage-head (cannonball) jellyfish

Stomolophus meleagris

Round, opaque, brown-rimmed dome that does look like a cabbage. Very common in late summer and fall, often washed up in numbers after onshore winds. Considered harmless to humans — sting is very mild.

Portuguese man o' war

Physalia physalis

Not a true jellyfish but a colonial siphonophore. Identified by a translucent blue-purple gas-filled sail, often with a pink crest, and long blue tentacles trailing below. Sting is painful and occasionally serious. Most often blown ashore on southeast winds in spring and fall. Even a washed-up specimen with no signs of life can sting if touched.

Sea nettle

Chrysaora quinquecirrha

Less common in Port Aransas than further north on the Atlantic coast, but occasionally seen. Translucent body with reddish stripes, long tentacles. Stings sting; rinse with seawater.

Box jellyfish (occasional)

True box jellies of medical concern are rare in Texas waters, but occasional sightings are reported. Treat any jelly with caution and report unusual species at the lifeguard stand.

When sting risk is highest

Sting risk is highest in late spring and early fall, when southeast winds blow Portuguese man o' war ashore. Cabbage-head jellies are most numerous in late summer and early fall but rarely sting.

Absent Rare Possible Peak
Jan
Essentially none
Feb
Essentially none
Mar
Early man o' war on south winds
Apr
Peak man o' war risk
May
Peak man o' war risk
Jun
Moon jellies common; man o' war drops
Jul
Scattered jellies
Aug
Cabbage-heads start arriving
Sep
Peak — cabbage-heads + return of man o' war
Oct
Peak man o' war risk on south winds
Nov
Tapering off
Dec
Essentially none

First aid if you're stung

Most jellyfish stings off Mustang Island are mild and resolve in a few hours. Portuguese man o' war stings are more painful and need attention. The wrong first aid (freshwater, ice, urine) can make a sting worse by triggering more nematocysts to fire.

Get out of the water calmly

Don't thrash. Walk out, then move to dry sand away from the surf line.

Rinse with SEAWATER, not freshwater

Freshwater changes the salinity around any remaining stinging cells (nematocysts) and can trigger them to fire. Use seawater, vinegar (5% household), or saline. Hot tap water is acceptable as a follow-up after vinegar to deactivate venom.

Remove tentacles with a hard edge

Use a credit card, plastic shell, or stick to scrape tentacles off — not bare fingers. Tweezers work too. Avoid rubbing the area.

Apply heat (hot water) for pain

Soaking the affected area in hot water (as hot as is comfortable, ~104–113°F / 40–45°C) for 20–45 minutes is the most effective pain reliever for man o' war stings, per emergency-medicine consensus.

Watch for severe reactions

Most stings cause local pain and a red welt. Seek immediate medical attention for: severe pain that doesn't ease with hot water, large or central body stings, breathing difficulty, chest tightness, dizziness, vomiting, or any sign of allergic reaction. Call 911.

Don't pee on it. Don't use ice.

Urine has variable salinity and isn't reliable. Ice and freshwater can both trigger more nematocysts to fire. Stick to seawater rinse, scrape, vinegar, then heat.

On the beach, give washed-up specimens room

A man o' war stranded on the wet sand can still sting for hours. Keep kids and dogs away. Do not pick one up to inspect it.

Jellyfish & Portuguese Man o' War — FAQ

When is jellyfish season in Port Aransas?

Peak sting risk is spring (April–May) and fall (September–October), when southeast winds push Portuguese man o' war into the surf zone. Moon jellies and cabbage-head jellies are most visible in summer and early fall. Winter and early spring are essentially jellyfish-free.

What does the purple beach flag mean?

Purple means dangerous marine life has been reported on the beach — typically jellyfish or Portuguese man o' war. Read it as a warning to stay out of the water or be prepared for stings. It's posted alongside the daily green/yellow/red surf-condition flag at public beach access points.

How do I recognize a Portuguese man o' war?

Look for a translucent blue, purple, or pink gas-filled sail (often the size of a balloon, 4–10 inches), often with a pink crest, floating on the water or stranded on the wet sand. Long blue tentacles trail below in the water — sometimes 30 feet or more. The whole organism looks delicate and almost iridescent. If you see one, give it (and any blue strings on the sand) a wide berth.

Can a washed-up Portuguese man o' war still sting?

Yes — for hours after stranding, sometimes longer. The stinging cells (nematocysts) can fire when touched even if the organism appears dead. Keep children and dogs away. Don't pick one up to inspect or move it.

Should I rinse a sting with freshwater?

No. Freshwater changes the salinity around any nematocysts left on the skin and can cause them to fire and inject more venom. Use seawater, 5% household vinegar, or saline. Hot water (as hot as is comfortable) applied after deactivating any remaining stingers is the most effective pain reliever.

Is peeing on a sting helpful?

No. Urine's effectiveness is unreliable — its salinity varies, and in some cases it can make the sting worse. Use seawater or vinegar instead.

When should I go to the ER for a sting?

Seek immediate medical attention for: severe pain that doesn't subside with hot water; large or whole-body stings; central body or face stings; chest tightness; difficulty breathing; dizziness; vomiting; or signs of allergic reaction such as swelling beyond the sting area or hives. Call 911 for anything severe.

Are there box jellyfish in Port Aransas?

True box jellyfish of major medical concern are rare in Texas waters, though occasional sightings are reported. Most Port Aransas stings come from Portuguese man o' war or sea nettles. Report any unusual jellyfish sighting at the lifeguard stand.

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