Carniolicum - Wildlife & Biodiversity in Slovenia: Alpine Longhorn Beetle

Friday, 12 July 2019

Alpine Longhorn Beetle - a dream comes true

Some animals are so charismatic, yet so elusive or rare, that the wish to see them escalates on every failed encounter. Sometimes they haunt you for years and you never seem to be lucky, no matter how much you try. For us this was the case with the beautiful Alpine Longhorn Beetle or Rosalia Longicorn Rosalia alpina, which until a few days ago, proved to be a mythical beast. This impressive longhorn beetle of the Cerambycidae family is rare on a European level and listed as vulnerable (VU) by the IUCN. Needles to say it is also a Natura 2000 species for which some special protection sites have been designated in Slovenia. Its life cycle is linked to the beech Fagus sylvatica and thus it is mainly found in mountain beech forests, especially those in warmer, sunnier areas of the Alps, but also other mountain and hilly areas of central and southern Europe. In Slovenia it is found in different regions, but nowhere in large densities. It is somewhat commoner in the Julian Alps, some parts of the Dinaric mountains and in some wooded hills of the Štajerska region. The essential element in its habitat is dead beech wood. Males and females are especially attracted to freshly wounded trees, but also cut timber and log piles. Apparently the smell of wounded beech wood proves irresistible to them. The easiest way to look for an Alpine Longhorn Beetle (but also other species of Cerambycidae, like the Beech Longhorn Beetle Morimus funereus for example) is to carefully check beech log piles in deciduous forests in July and August.

A few days ago we visited the Trenta valley at the heart of the Triglav National Park in the Julian Alps, with the intention to look for this rare longicorn. This time we were finally successfull as we found a nice log pile at the side of a road, where up to 5 stunning Alpine Longhorn Beetles were sunbathing!

Alpine Longhorn Beetle Rosalia alpina

The adult Alpine Longhorn Beetles emerge in summer and can be seen basking in the sun, mating or depositing the eggs on the logs. Sadly these log piles act as traps as they are taken away from the forest, with whole broods of longhorn beetles, which are subsequently destroyed during the industrial processing of the timber. A simple measure to avoid this would be to quickly remove the logged trees from the forest, before the beetles could lay their eggs in them. Another measure to help longhorn beetles is to leave some log piles in the forest without removing them. This is exactly what the Triglav National Park has done recently by placing a permanent log pile and an info board about the Rosalia Longicorn along a tourist trail in the Trenta valley. Now in the summer months visitors can read about this rare beetle and with a bit of luck, spot one basking on the logs. After finding our own longicorns at another site, we also payed a visit to this demonstration log pile called Rosalium, where amazingly 3 more Alpine Longhorn Beetles were there for all the visitors to enjoy. Very didactic!

The "Rosalium"

A tame Alpine Longhorn Beetle Rosalia alpina decided to land on my hand. Yes, the can fly!

The longhorn beetles could have been enough to make our day, but the Trenta valley provided some other interesting wildlife. Among birds we saw several Crag Martins Ptyonoprogne rupestris and heard a Western Bonelli's Warbler Phylloscopus bonelli, while butterflies of note included Styrian Ringlet Erebia stirius, Mountain Green-veined White Pieris bryoniae, Chalkhill Blue Lysandra coridon and Arran Brown Erebia ligea.
We were also very glad that Mitja Denac gave us a tip on where to see Creeping Lady's-tresses Goodyera repens - a tiny orchid sprouting in summer under conifer trees. It was a lifer for us! Finally we also enjoyed in seeing good numbers of the rare Tufted Horned Rampion or Devil's Claws Physoplexis comosa, although they weren't in full bloom anymore.