Discovering the Rosalia Alpina: Unveiling the Hidden Jewel of the Forests

The Alpine Rosalia: A Quest for the Brilliant Blue Beetle

In July, the Alpine Rosalia beetle emerges, presenting a prime opportunity to witness this dazzling blue insect. Join us in the Swiss mountains, where we meet with an entomologist eager to spot this rare creature.

This article is published in collaboration with .

Fully (Switzerland), report

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Perched on a south-facing balcony in the heart of the Swiss Alps, today might be the day we finally encounter a creature that seems to belong more to the tropics or a fairy tale than to these latitudes. This large insect, known as the Alpine Rosalia, sports a striking blue shell tinged with ink-black and long, curved antennae, making it a rare sight in this region. The Alpine Rosalia is elusive, its sightings fleeting, and its numbers dwindling.

Yannick Chittaro greets us with a smile against a backdrop of cloudless mountain skies. He has chosen this location because the forests here are full of ancient trees with plenty of hollows—perfect for wood-dependent beetles like the Rosalia. Despite the early hour, it’s already sweltering at 9:30 AM. “This is perfect weather for this sun-loving beetle, active on the hottest days of the year,” our guide for the day beams. “I’d say we have a 50% chance of spotting one.” Yannick knows this area well, having conducted numerous entomological surveys here.

We bump along a rocky road in his small car, nets, beetle traps, and other scientific paraphernalia rattling around in the back, accompanied by the chorus of cicadas drifting in through the slightly open windows. “These steep, sparse forests are ideal: hard to exploit, they contain old trees that dry while standing, maximizing sun exposure,” Yannick analyzes as the landscape whizzes by. “But that’s not all; specific types of trees are needed. The Rosalia’s favorite is the beech, and here occasionally, the sycamore maple. Elsewhere in Europe, you might find them in ashes, willows, maples, lindens, or elms. Moreover, for a tree to be chosen as a meeting and breeding place, the diameter of the trunks or branches must be at least 20 cm, ideally over 50 cm.”

Meeting the Rosalia is a dream. But is it akin to finding a needle in a haystack? We step out of the car and onto a trail overwhelmed by hazelnuts. The first task is to find a dying or dead beech tree. “Broken by wind, frost, or the weight of snow, struck directly by lightning or a falling rock, or simply worn out by time,” Yannick lists the possible conditions of the trees we’re looking for. Forest management practices can increase potential habitats if high stumps are left in place. These sites serve as meeting and breeding grounds for our blue and black beetle.

A venerable beech, locally known as ‘foyard,’ stands before us, its bark partially stripped. The insect enthusiast inspects it meticulously, explaining the typical fate of a Rosalia egg laid in a bark crevice: “A small white larva hatches and begins to burrow a tunnel with its mandibles. It feeds on the wood and burrows deeper, compacting the sawdust against the walls instead of excavating it, leaving little trace of its presence. This allows it to eat and grow in relative safety—or almost.” A woodpecker might end this safety with a few well-placed pecks. Another, more insidious danger lurks if the egg is laid in a log cut and left temporarily in the sun, a highly attractive breeding site, as the woodworm could end up in a sawmill or stove before completing its lifecycle.

“The local forestry service, which we work with, is aware of these issues,” Yannick continues. “Cut wood is quickly cleared away. Clearings are also made around key old trees left standing for woodboring insects.”

No longhorn beetles on our first beech tree. With confident strides, the entomologist heads down the slope towards a clearing flooded with harsh sunlight. It’s hard to keep up with his long steps amid the jumble of fallen trunks. His trained eyes sweep the area, his hands shielding the sun. From ground to sky, close and far, everything must be checked. A Rosalia might be hiding in the foliage or camouflaged on the bark.

If no adults are visible, could we possibly uncover some larvae? “Yes, if we take an axe to it… Which we’re not going to do, of course,” he jokes. “These white sausages bore tunnels where the fibers are still hard enough, at the level of the heartwood and sapwood. There’s no use looking for them in decayed parts.”

With both larvae unreachable and adults unseen, our quest is challenging. Rosalia, give us a sign! While examining an old stump, net in hand, Yannick shares that a Rosalia larva lives two to three years in the darkness of its shelter, progressing along its tunnel as it feeds. Before its final hibernation, it turns back towards the periphery.

In spring, when it reaches about 4 cm in length, it carves out a small chamber under the bark to transform into a nymph. The immobile, ivory-white creature already has antennae and legs, tucked against its body. It gradually gains color. Finally, in summer, from June to August depending on the region, a magnificent blue and black insect emerges to take flight.

Our initial enthusiasm has somewhat faded. “With the early heatwave this spring, we might be a week too late,” Yannick worries. “Last year, right here, I saw up to six individuals running up a trunk, males trying to push each other away in the presence of a female.”

It’s all about timing. After spending years in total darkness as larvae, Rosalias only flit about in the light for about ten days. “During their short adult phase, all their efforts are dedicated to reproduction. They hardly feed, at most licking the sap that flows from beech trees,” explains the man who fell in love with insects in his childhood.

Rosalia, have you moved on to other realms? We change locations one last time. Near a bench at the crossroads of two paths stands a centuries-old beech known as the ‘lover’s tree.’ Its species not well-suited to extreme droughts, it’s a wonder how it grew here, alone among downy oaks, pines, and field maple trees.

Once majestic, this tricentennial partially collapsed under a gust of wind ten years ago. Despite its isolated location, it has hosted about ten generations of Rosalias. “But this year, it seems almost too old and dry for the larvae. It’s all about balance. Moreover, the undergrowth and ivy cast too much shade and could hinder the adults’ flight,” Yannick laments.

It’s time to head back. In this stifling atmosphere, our hopes are dwindling. The flight holes peppering the old tree trunk seem merely a memory left by past Rosalias. But Yannick makes one last check out of due diligence… And suddenly cries out in victory! Can you believe it? Two large blue commas adorned with black tufts emerge behind a root. What a marvel! Slowly, the creature begins to climb its tree.

Staying against the bark for camouflage, it gently folds its antennae against its body each time it passes under the clinging vines. “In longhorn beetles, these long appendages are the main sensory organ, the seat of smell. Their vision is probably quite poor,” he details while positioning his hand next to the insect, unflappable, to gauge its size. The nearly 3 cm long body appears as soft as velvet, and its markings resemble a strange mustachioed face.

“Another Rosalia in flight!” Yannick exclaims. It was likely attracted by the pheromones of the first or by the scent of the beech. In blinding light, it lands somewhat clumsily at the top of the old sage. It blends perfectly onto the bluish bark. “This is probably one of the last years we’ll see them on this beech,” the entomologist muses thoughtfully.

Rosalia, if only you knew the joy we feel in meeting you, just in the right place, at the right time.

This article is from the series, “Rosalia and Company.”