Prospekt Fauna, Intresting facts

Photo 1. The black-veined moth Siona lineata in Leska Valley in Risnjak National Park (Photo by M. Randić)


From a recent excursion to the hinterland of Rijeka I brought back an unusual yellow cocoon containing the pupa of an unknown butterfly. I waited to see if anything would emerge from it.

The yellow cocoon was four centimetres long and had a parchment-like texture. The surface was covered in loose threads of yellowish silk. At first I thought the cocoon belonged to a moth species of the family Zygaenidae. However, on 30 May when a white moth with dark veins on its wings (Photo 1) emerged from the cocoon, I realized it was a black-veined moth Siona lineata of the very large family of geometer moths, Geometridae.

In Gorski Kotar, I have previously come across this species at Crni Lug (Photo 2), Zelin, Lič, Fužine and Delnice, as well as in the marginal parts of Gorski Kotar near the Littoral: at Kamenjak, on the edge of Grobničko Polje, at the foot of Mali Platak and above Plase. The Blaž doline in the hinterland of Krasica is the lowest location, closest to the sea, where I have spotted the black-veined moth.

This moth can be found in the field from the first half of May to the last week in June. Typically, the late afternoon is the time of day when they are most likely to be seen flittering around. Most often, they prefer lush continental habitats, as well as certain types of sub-Mediterranean grasslands. The latter are characterized by a somewhat particular ecology. Namely, in the early morning heavy dew often forms on these grasslands, while at twilight colder air flows over them.

Temperatures taken of the layer of air close to the ground and surface layers of soil at the bottom of the Blaž doline indicate that a “lake” of cold air hovers over the meadow, especially in the early morning and evening (and probably during the night), making the bottom of the doline a frost pocket (Photo 3). When there is no wind on a clear day, the air at the bottom of the doline heats up quickly and in these conditions the temperature in the doline is usually a few degrees higher than the temperature along the doline edges. It seems that the (micro) climate conditions of the meadow at the bottom of the doline suit the black-veined moth, at least in these sub-Mediterranean areas close to the sea, one of which is the deep Blaž doline, a frost pocket in the hinterland of Krasica.

Marko Randić

Photo 2. The black-veined moth is often attracted to the flowers of the field scabiosa (Knautia sp), a nectar-producing plant. (Photo by M. Randić)

Photo 3. The meadow at the bottom of Blaž doline, where air and soil temperatures were measured. It can be noted that in the springtime the trees on the bottom of the doline sprout leaves later than the trees on the slopes of the doline, indicating that the bottom is a frost pocket, in which frost can form even in springtime. (Photo by Ana Randić and Nina Randić)