Anguis fragilis Linneaus 1758

Elmberg, Johan, 2023, Amphibians and reptiles in North Sweden: distribution, habitat affinities, and abundance (Classes: Amphibia and Reptilia), Zootaxa 5301 (3), pp. 301-335 : 319

Slow Worm Anguis fragilis Linneaus 1758

Distribution ( Figure 8 ). Included records from Artportalen (N=360): as there are not any confusion species all reports have been included.

Common and widespread in the Southern Boreal and the coastal southern part of the Middle Boreal. From Medelpad and northwards all records have been made within 60 km of the Baltic coast.

The vast majority of records is from coastal areas or low altitudes in river valleys. Nevertheless, there are several records from above 300 m altitude in Hälsingland and Ångermanland, and a photo-documented occurrence at 425 m in Medelpad (15 km SW of Stöde).

Although most common near the coast, the total lack of records from offshore islands in North Sweden indicates poor dispersal capacity over brackish water.

There are no indications of changes in distribution during the last 50 years. Note, though, that the northernmost occurrence presented in the map ( Figure 8 ; lower Byske River valley and the adjacent Tåme area to the north (Västerbotten )) became publicly known as late as 1989, despite the species having been known locally since at least the 1920’s ( Södermark 1989). This occurrence has long been regarded as a disjunct population ( Elmberg 1995) and perhaps the result of anthropogenic spread, but recent records around Skellefteå have gradually closed the previously supposed 70+ km distribution gap.

Habitat and movements. In North Sweden this is the only reptile regularly encountered in closed forest, particularly in mesic stands with scattered deciduous trees and protective undergrowth. However, the most widely used habitats are fairly open, yet with denser undergrowth than those preferred by Vipera berus and Zootoca vivipara : forest edges, natural grasslands, shores, and rock outcrops. Most sightings of Anguis fragilis are made in anthropogenic habitats such as clear-cuts, fields, meadows, roadsides, and near recreational buildings ( Figures 13 , 19 ).

Although it is the only reptile in North Sweden frequently seen active in cloudy weather, its general habits are seclusive. Shelter is typically found under flat stones, haystacks, compost piles, sheet metal, woodpiles, and tarps, in other words often under man-made objects. This habit may facilitate inadvertent anthropogenic spread.

Daily and annual movements have not been studied, including any seasonal variation in habitat affinity.

Subterranean hibernation sites are most likely found in or very close to the summer habitat, but nothing is known about hibernation habits in North Sweden.

Abundance estimates and trends. There are not any published abundance data, but estimates based on extensive field work in the Umeå area (Västerbotten) 1975–1994 run in the neighborhood of> 200 adults /km 2 in landscapes with mixed habitat near the coast (Elmberg, unpublished, Stefan Andersson, personal communication) .

There are no indications of changes in abundance over the last 50 years.

Figures

FIGURE 8. Distribution of Anguis fragilis in North Sweden. The oval in northernmost Västerbotten represents many records over a long time period, a population that is possibly disjunct. Note the total lack of records from offshore islands in the Baltic.

FIGURE 13. Recently abandoned hayfields are prime summer habitat for Rana temporaria, R. arvalis, Bufo bufo, Anguis fragilis, and Vipera berus. The forest edge in the background is typical habitat also for Zootoca vivipara. Baggböle, Västerbotten, Middle Boreal region. Photo: Johan Elmberg.

FIGURE 19. Clear-cuts offer summer habitat for Zootoca vivipara, Anguis fragilis, and Vipera berus for a decade or so until planted conifers grow tall enough to shade the ground. Robertsfors, Västerbotten, Middle Boreal region. Photo: Johan Elmberg.