I came to Runmarö to meet a peculiar entomologist with a gift for digression, and to try to understand the secret life of the Baltic island he has lived on for nearly 30 years. It is a place just an hour away from Stockholm, but accessible only by boat, whose complicated natural and literary history is encoded in a landscape of deceptively simple beauty.

But first I had to survive the Swedish midsummer festival. This annual bacchanal – pegged to the solstice, dressed up in folk costume and steeped in Viking meaning – happened to coincide with my visit. I remember the herring and the new potatoes, the ring dance around the maypole, a song about a frog, the fetching girls with wildflowers in their hair, the shameless boogieing to Abba. The rest is gone, washed away in a river of aquavit and brännvin.

The next morning, emphatically hungover, I awake to find Fredrik Sjöberg puttering away in his Wellington boots. He invites me into his study. I try not to make too much of the fact that on his desk he has a bottle of cyanide, his preferred method of killing the bugs he traps and pins down. His collection numbers 211 species, all found on the island, all hoverflies.

Sjöberg is exclusively interested in this family of insects, Syrphidae, which is distinguished by an uncommon flair for disguise. While harmless, Syrphidae have adapted, so that they look like stinging or biting bugs, mostly bees or wasps. To capture them, Sjöberg uses a net and a long tube called a pooter, a kind of fibreglass straw from which he inhales, sucking the fly into a cylinder backed with a mesh filter that prevents it continuing down his throat.

Sjöberg wrote about his entomological exploits on Runmarö in a thin, wry, at times poetic, memoir called The Fly Trap. As far as books about bugs go, this one was a minor sensation, selling 30,000 copies in Sweden alone, which led to popular translations all around Europe and to two more books in the series.

Rusticated existence

When not hosting midsummer ragers, Sjöberg lives a quiet, rusticated existence with his wife, Johanna, who runs a bookbindery out of the simple cottage they bought on Runmarö in 1986. They raised three children here in an environment of pastoral grace and occasional privation, where water came from a well and they showered with a bucket.

“We were young and stupid,” Sjöberg says. “People thought we lived this way because of the romance, some environmental nonsense. But the truth is we had very little money, and we really struggled.”

Today, he adds, his little cottage has grown in value 10 times over as Runmarö, along with many other islands in the Stockholm archipelago, has become attractive to city dwellers who can pay a small fortune for the Swedish dream, a little rust-red house by the sea.

The archipelago consists of a few thousand islands in a 50-mile-wide band that buffers the Swedish capital from the Baltic. No one can agree on how many islands there are: published reports vary from 10,000 to more than 50,000, although many of these are little more than limestone skerries, destinations for the curious seal only. About 100 of them are linked by a network of efficient, state-run ferries.

These islands have long been a kind of escape hatch for Stockholmers, something like a Nordic Cape Cod. This is where Benny and Björn from Abba went to write songs, where Mikael Blomkvist hid out with the girl with the dragon tattoo, where Swedes of every stripe indulge in their national pastimes of camping, sailing and skinny-dipping.

On approach, Runmarö looks like any other isle in the archipelago. Little docks shoot out every which way from stone outcroppings. Walking off the ferry, you’re quickly surrounded by pastures of wildflowers and clapboard houses painted in the distinctive matte red called Falu. (Made from a natural pigment derived from a copper mine, this paint became popular because it was so cheap; now it’s fashionable, part of the Swedish heritage brand.)

Resort

Runmarö was among the first islands in the archipelago to be exploited as a resort. Many artists, particularly writers, spent summers there. Among them was the dark and dangerous playwright August Strindberg, who wrote a novel there and conducted a tempestuous affair with his Danish lover, and Tomas Tranströmer, the Nobel laureate who died in March.

Tranströmer, who was the 20th century's most translated poet after Pablo Neruda, grew up on Runmarö and spent most of his summers there in the house that his grandfather built in the mid-1800s. The island is written all over his work, especially his first collection, 17 Poems.

Today, Runmarö is more popular among orchid hunters and lepidopterists than among writers. Its calcareous soil has produced one of the richest concentrations of natural life in Scandinavia. Herbaceous forests of young pines covered in lichen give way to bogs concealing rare species of carnivorous plants.

Sjöberg has become an authority on the island’s microclimate. In summer, you can find him standing perfectly still in the sun, sometimes for hours, perched atop raspberry thickets or wild chervil. Passersby might suspect he’s lost in meditation, and, as he says, this is not wholly inaccurate.

After breakfast, Sjöberg leads my wife, Yana, and me on a hike to the most remote of Runmarö’s nine freshwater lakes. The path curves around cottages fenced in by rows of conical candy-coloured flowers and empties out into the forest. Somehow, the smell of sea water is sharper here, just as Tranströmer observed. This is the Baltic “sighing in the middle of the island.”

Our destination, Silver Lake (Silvertrasket), takes its name from local legend. When Russians raided the archipelago in the 18th century, fearful residents apparently sunk their silver in the lake. Once out of danger, they tried to dredge it up, but the silver was never found, so the lake was presumed to be bottomless. Later, fishermen reported ghost sightings, and as a result no one fished the lake and no one built houses around it. Strindberg folded the legend into a short story that he set here, written in 1898 and later published in the German avant-garde journal Quickborn, with eerie illustrations by the painter Edvard Munch.

Wet ground

The ground becomes wet: wild rosemary and cottongrass have come here, and young pines stand as straight as fence poles. There is a knocking, as at a night-time door by a latecomer: it is the woodpecker. There is a whimpering and moaning, as of a woman in childbirth: it is the wood dove.

Sjöberg knows all the sounds, he knows all the plants and animals, so that if he heard or saw something unfamiliar, he would take it as an affront.

He spends a lot of time in his book joking about flies, about how no sensible person is interested in them, “or, anyway, no woman”.

He ascribes his hoverfly hunting to a pedantic impulse to know one thing, any thing, inside and out (what Strindberg derisively terms “buttonology”) and to the pleasure of “exercising slowness” in a world that’s moving ever faster. Ultimately, he says, none of that is quite right: the flies are actually metaphors, “glosses”, a way of not merely looking at nature but of reading it as if it were a book.

This nature-as-language theme is his great takeaway, a kind of challenge not just to be captivated by the superficial romance of the outdoors but to practice “landscape literacy”, to understand its constituent parts.

“I’m afraid,” Sjöberg writes, “that our path to what is beautiful must first pass through what is meaningful.”

We bid farewell to Sjöberg, intending to spend our last few days in Sweden island-hopping. The 10-minute boat trip from Runmarö gives us barely enough time to reminisce before we’re dropped at Stavsnäs harbour. A quick taxi ride takes us to Djurönäset, a resort complex that dominates the island of Djurö, one of the last sections of the archipelago that can be reached by car from Stockholm via a series of small bridges.

The hotel is by turns luxurious and austere – call it sanatorium chic – and is designed around the natural features of the island, with hammocks hung between tall pine trees and benches nooked into moss-covered rocks. Some accommodations are made to look like the traditional cottages you see on islands such as Runmarö.

All this — and the proximity to the harbour, where you can catch boats to take you to islands farther afield — makes Djurönäset an excellent base for exploring the archipelago.

Birchwood-fired sauna

The islands beckon, but so does the hotel’s birchwood-fired sauna, perched in a spacious shack at the water’s edge. A small dock leads to the brackish, bracing waters of the Baltic. When we have enough heat, it’s time to jump in.

We rinse and repeat several times, before throwing on robes and collapsing on wooden chaises.

The next morning we taxi back to the harbor and board a boat to Sandhamn, the fanciest and most remote of the islands in this section of the archipelago. We scurry along the port, escaping yachts blasting techno, and stop by a bakery for fika, a kind of second breakfast, a wonderful concept that Sweden should export to the rest of the world in lieu of a trillion tons of particle board.

We take our coffee and our fresh cardamom buns to the terrace, bound by a red picket fence. The sun, a coy little tease during most of our trip, finally emerges. Everything is perfect. But then a wasp menaces, landing on our table.

I remember Sjöberg's disquisition on hoverflies, about how they masquerade as stinging insects but how you can read their true nature in the number of wings: Syrphidae have two, whereas bees and wasps have four.

“Don’t worry,” I say, counting the wings, or maybe just pretending to. “That’s only a hoverfly.”

If you go

Runmarö and the islands in this section of the archipelago are accessible by ferry from Stavsnäs Vinterhamn, a harbour that's about an hour from downtown Stockholm. The website of the state-run ferry company Waxholmsbolaget posts schedules in English at waxholmsbolaget.com.

Commercial life on Runmarö consists of just one bakery, a grocery store and a seasonal restaurant and bar, Svängen, that serves pizza. For those who want to spend the night, consider Anders Olofsson's lovely, if rustic, accommodation, Tarnviken, which is surrounded by a rose garden. It costs from 230 Swedish krona (about €24.75) per night per person , as well as a one-time charge of €35 per person for linens). See tarnviken.se.

Djurönäset Located on Djurö, a five-minute drive from the Stavsnäs harbour, this sleek Nordic spa resort is an excellent base for exploring the archipelago, complete with a dockside restaurant, a birch-fired sauna and accommodations styled like many of the little cottages you'll find throughout the islands. Double rooms cost from 1,790 krona (€190) a night. See djuronaset.com.

Sandhamn

Popular with the moneyed sailing set, Sandhamn is one of the few islands in the middle archipelago with serious hotels and restaurants. The fresh-baked cardamom buns at the Sandhamns Bageriet, at the northern tip of the port, are alone worth the ferry trip.

At the other end of the port are Monrad's (monrads.se/sandhamn), a cafe that sells provisions for sailors and serves delicious house-cured gravlax and bleak roe, and the elegant nautical-themed Sandhamn Yacht Hotel (sandhamn.com), from 2,300 krona (€240) per night. – The New York Times Syndicate