Sand Fleas and Other Flaws

Sand-flies a flying, or sand fleas a fleeing
I shan’t discuss; I’d rather be freeing
My mind on more weighty affairs and things,
Like angels’ wings and serpents’ and spiders’ stings.

Arthur Clifford Hawes, 1893, The Muse Poetic: In Eight Cantos (Canto III, XXIII)
Topsail Beach, North Carolina. Photo by Trish Weaver

Unlike Arthur Clifford Hawes who wrote the poem above, I feel a pressing need to discuss sand fleas. Imagine if you will… a time, before or after social distancing, when you can go to the beach. Let’s say you live in the southern United States, and you’ve decided to go fishing, but you don’t have any bait… then it dawns on you and you say to yourself, “I know! I’ll go down to the swash-zone and dig up some “sand fleas”… Yippee! problem solved.”

Now let’s say you live in the northeastern U.S. and you decide to take a stroll along the beach in the evening. As you’re walking you notice small critters ricocheting off your feet and ankles. “Sand fleas!”…how annoying.

Or maybe you’ve been to the beach in either of those places and you’re noticing red, itchy welts on your lower extremities…Dang it! “Sand fleas!”

Or perhaps you’ve been on vacation in a sub-tropical paradise, say Central or South America, and suddenly you’ve got oozing white pustules, with black dots on your feet…Dang and Blast! “Sand fleas!”

Or perhaps, you’re me giving a tour of the NCSM Invertebrate Paleontology Collection and are showing your visitors some fossil frog crabs, when someone asks are these related to …wait for it…”sand fleas?!” It’s then you realize you’ve got problems….

A fossil frog crab, Ranilia sp. from the Pliocene Intracoastal Formation, Florida. This specimen is in the NCSM Invertebrate Paleontology Collections and causes me no end of grief. Photo by Trish Weaver

So, what are all these creatures we call sand fleas? They can’t all be the same thing, can they? and by golly what do people on the west coast call sand fleas? Let’s take it region by geographic region shall we?

This is not a sand flea, it’s a mole crab, Emerita talpoida. But it does make great bait. Photo by Bronwyn Williams

If you’re in the south and are fishing with “sand fleas” as bait, you’re actually fishing with mole crabs, “sand crabs,” “digger crabs,” or what New Englanders like to call “beach bugs.” Mole crabs are decapod crustaceans, infraorder Anomura (different tail), genus Emerita. Mole crabs do not have pinchers, and though they have mouths to eat with, they do not “bite” humans…but they do tickle. Mole crabs are a tasty snack for shore birds and a variety of fishes, thus they make good bait. The genus Emerita is common along both the Pacific and Atlantic coasts of North America, and the Atlantic coast of Africa. Mole crabs are somewhat oval shaped, have a hard exoskeleton, and are spectacular burrowers. When burrowing, they dig into the sand butt-first, sometimes leaving their antennae exposed to catch plankton and other detritus to eat. Unlike most true crabs, Mole crabs can only move backwards, rather than from side to side. Again, they don’t bite, or hop per se, so why people call them “sand fleas” is beyond me.

This is also not a sand flea. It is talitrid amphipod. These are also known as beach or sand hoppers. Photo by Phillip McErlean / CC BY-ND 2.0

If you’re in the Northeast or really anywhere, and are walking along the beach in the evening, those “sand fleas” pinging off your legs and feet are actually amphipods. Most likely belonging to the family Talitridae. These “land,” “sand,” or “beach” hoppers, sometimes even called sand shrimp (don’t get me started), live near or above the high-water mark. During the day, to avoid drying out, they mostly shelter in burrows in the sand, under rocks, or under seaweed that has washed ashore, but at night and early in the morning, they hop around in search of detritus. Yep… detritus! Not your feet or legs! Once again, the name sand flea is a misnomer, as talitrid amphipods don’t bite people…but they do hop really well and it can be pretty annoying to have them colliding with your legs and feet while strolling along the beach.

Also, not a sand flea. A biting midge on human skin. Photo by CSIRO / CC BY 3.0

If neither mole crabs nor talitrid amphipods are biting me, then what is? What IS causing those itchy red welts? Sand fleas? Whelp… that’s good question…which doesn’t necessarily have a good answer. There are many different organisms they could be biting you including sand flies, biting midges, and other “no-see-um” insects. Yes, insects! But biting midges in the family Ceratopogonidae are likely the culprit. There are over 5,000(!) species within this family. These annoying insects live all over the world and are incredibly tiny (adults generally 1-3 mm in length), hence the common name “no-see-ums.” Adults are usually gray and when viewed under a microscope look like miniscule flies. To be a bit more specific it’s likely ceratopogonid females of the genus Leptoconops are making you itchy, because they burrow in moist, usually saline, sand or mud of coastal and inland beaches, have a global sub-tropical to tropical distribution, and are diurnal feeders on vertebrate blood. Their bites are painful and can cause itchy lesions. So now, we’ve got insects that live in the sand and bite, but still aren’t fleas.

What the heck is a “sand flea?”

Finally, an actual sand flea or jigger, Tunga penetrans. Photo by Michael Wunderli / CC BY 2.0

For the answer we have to travel to Central or South America, the Caribbean, Sub-Saharan Africa or Madagascar… Awesome! I’d love to go to those beaches…But wait…”Sand fleas!” True sand fleas are indeed fleas, like the ones you worry about your pet having, that live in the sand in these regions. Also known as chigoe fleas or jiggers (not to be confused with chiggers, which are mites), sand fleas, Tunga penetrans, are nasty little bugglelies. These wretched creatures live in the sand, are parasitic, and cause an inflammatory skin disease known as Tungiasis.

The female of the species uses its proboscis to create an opening, or lesion. Then it burrows head-first into you, leaving the butt end of its abdomen visible through a tiny hole in your skin. This hole allows the flea to breathe, defecate, mate, and expel eggs while feeding on you. YUCK!

That hole in your skin is kind of like a snorkel…

From Tom and Jerry 1945 short “Tee for Two”

While embedded in your skin the female’s midsection swells to about the size of a pea. At this point, the outer layer of your skin is stretched thin, resulting in a white halo around a black dot which is actually the butt end of the flea. From there, the flea dies under your skin after releasing its eggs, which drop to the ground. Ew!

Do yourself a favor, don’t look any of this up, you really don’t want to know. Good news is we now have a flea that lives in the sand and can correctly be called a sand flea. Yippee! Sand fleas!

Frog crab, Ranilia murcata, from the NCSM Non-Molluscan Invertebrates Collection. Photo by Bronwyn Williams

Hang on a second…how are any of these “sand fleas” related to the fossil frog crabs in the Invertebrate Paleontology Collection that started this whole diatribe? Well… none of the aforementioned “sand fleas” are closely related to frog crabs. Frog crabs, like mole crabs, are decapod crustaceans, but frog crabs are actually true crabs in the infraorder Brachyura (meaning short tail, technically abdomen), family Raninidae. Like mole crabs, frog crabs are great burrowers and can only move forwards and backwards, but unlike mole crabs they do have pinchers. When moving through the water they look like frogs hopping hence the name frog crab. Not sand fleas at all.

Frog crab, Ranilia murcata, showing its pinchers. Specimen from the NCSM Non-Molluscan Invertebrates Collections. Photo by Bronwyn Williams.

After all of this I still don’t know what folks on the west coast of the U.S. call “sand fleas” but perhaps someone who lives there will chime in and let us know. For now, I think I’ll take A.C. Hawes sage advice and will free my mind to think about “angels’ wings and serpents’ and spiders’ stings”


Thanks for joining us. If you would like to follow the everyday adventures of our lab, check us out on Twitter and Instagram at @BWWilliamsLab. We hope you enjoyed this awesome story as much as we did. If so, please share it with your friends and let us know in the comments! Signed, the NMI Lab.

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