It was a simple question, from one who was (literally) irritated.

After a friend received multiple jellyfish stings on a beautiful beach day, she asked what are these gelatinous globs are good for, anyway? The answer might be more than you think.

The easy and usual response I offer is that jellyfish feed sea turtles, especially leatherbacks, and, also, ocean sunfish. However, with some research, I found a few other interesting benefits of this often-maligned sea creature.

This month, there have been lots of reports of jellyfish, from Lucy Vincent to State beaches and many locations in between. Different species have been suggested as the offending jelly, but it wasn’t until an inquiry and photo from a few State Beach Path 13 regulars that I got my arms (or tentacles) around the identity of one of the culprits.

The key photo one of them sent me was almost like a mug shot. It showed me that the cause of the harm on this beach was (as Hooper from Jaws would say) no boating accident, nor any propeller, and it wasn’t any coral reef, and it wasn’t Jack the Ripper. It was a sea nettle.

Sea nettles have been floating among the swimmers at State Beach throughout August. Sea nettles are saucer-shaped jellyfish with four frilly oral arms and four to 40 long, thread-like tentacles. Their bell can be two to eight inches wide, and with the tentacles the animal can extend to seven feet long.

The coloring of sea nettles can be very variable, though pictures of this jellyfish most often show shades of white and pink, which led to quite a case of confusion in this summer blockbuster mystery with another jellyfish find.

Seven-year old Nash Verbeck from Nashua, N.H., caught a jellyfish at State Beach with red spots at the top and radiating down the bell. His jellyfish had a few short, fat oral arms, but it lacked the long tentacles usually seen on sea nettles.

His family and friends were quite excited to have stumped this naturalist. And, not to be outdone, I returned to my research and eventually found a match. Nash likely also had a sea nettle, though it was a juvenile that hadn’t yet grown its longer tentacles and appeared to be a red-brown color morph of the species.

My research also informed me that these creatures — surprisingly — also have benefits that extend to other animals and even to humans. A few stand out.

Sea nettles are carnivores and will eat mosquito larvae, among other things, which certainly depletes the number of these buzzing biters before they metamorphose into adults.

More surprisingly, I found some of their interactions with species we appreciate.

In a creative coupling, blue crabs enjoy a symbiotic relationship with sea nettles, riding atop their bells while cleaning off and eating debris and parasites. Juvenile spider crabs hang around sea nettles too, living under the bell and feeding on the jelly’s mucus and tissues. Harvest fish will shelter in those long tentacles, and nudibranchs prey on sea nettle polyps, stealing their uncoiled (and unused) stinging cells, called nematocysts, to store and use later as defensive tools.

Perhaps the most interesting interaction is with oysters. Though sea nettles were once thought to be predators of this bivalve, eating oyster larvae, and thus a bane to oyster farmers, it is now believed that sea nettles are allies of sorts. Sea nettles do eat oyster larvae, but strangely, they don’t digest them. They spit out these oyster babies live and healthy, preferring to consume ctenophores, more widely recognized as comb jellies, which do actually consume larval oysters. By taking out oyster predators, and thereby giving the oyster young some temporary protection, sea nettles can actually help larval oysters survive.

So with sea nettles, one must take the good with the bad. Shakespeare accurately summarized the oysters’ position when he said, “out of this nettle, danger, we pluck this flower, safety.”

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature.