Insects and arachnids on the Faroe Islands

The painted lady (*Vanessa cardui*) is a migratory butterfly that migrates north from the Mediterranean region in spring. It is a strong flyer and can reach as far north as the Faroe Islands and Iceland. In some years, it can appear invasive, as in 2019, when painted ladies appeared in large numbers in many places on the islands. The painted lady does not tolerate frost, and the butterflies seen in the Faroe Islands in summer are therefore all migrants from the south.
JOHNNY MADSEN/BIOFOTO/RITZAU SCANPIX, 2019

The terrestrial invertebrates in the Faroe Islands are represented by insects, arachnids, molluscs, annelids and flatworms. The following describes insects and arachnids, which are the two classes of invertebrates that you are most likely to encounter on the islands.

A total of 1,355 different species of insects have been registered, which are divided into 14 orders. With 374 species, diptera, i.e. mosquitoes and flies, constitute the largest order. The largest number is seen among lake flies (Chironomidae spp.), which in the Faroe Islands comprise 80 different species. Lake fly larvae live in water and are common at the bottom of streams and lakes where they can appear at quite great depths. Another mosquito that has attracted some attention is the heather fly Bibio pomonae, which suddenly appeared in large numbers in Tórshavn in 2018, although, until then, it had only been common on Suðuroy. There are also the ubiquitous blow flies, which are divided into five species, while there are 12 species of crane flies.

Certain diptera are closely associated with domestic animals. This is the case for, e.g., golden dung fly (Scathophaga stercoraria), whose larvae live in sheep dung, and sheep ked (Melophagus ovinus), which are flies that live in the wool and suck blood from the sheep.

Hymenoptera include bees, wasps and ants and number 273 different species. The vast majority are ichneumon wasps, the larvae of which complete their development inside other animals, especially butterfly larvae. The ichneumon wasps are often very small and several have no wings. More widely known and easier to spot are common wasps (Vespula vulgaris) and white-tailed bumblebees (Bombus lucorum), which also belong to the hymenoptera and today are found on several of the islands.

It is particularly noteworthy that a total of 227 different species of lice have been recorded. That is not only because different bird species are hosts to different lice, but also because conservationist and nature guide Jens-Kjeld Jensen on Nólsoy has done a marvellous job of finding and recording new species of lice on the islands.

Beetles are represented by 219 species, several of which are closely associated with the fresh waters. Among the most impressive terrestrial beetle species is violet ground beetle (Carabus problematicus), which you will probably come across if you lift stones in the outfield. With a length of 23‑30 mm, the beautifully violet-shining ground beetle is probably not the largest, but likely the heaviest insect in the Faroe Islands.

Some of the 166 different butterfly species that are registered in the Faroe Islands are vagrants that occasionally make their way past the islands. This is the case for e.g. red admiral (Vanessa atalanta) and painted lady (Vanessa cardui), both of which migrate north in the summer months and in certain years can appear in such large numbers that some of them end up in the North Atlantic area. However, they are not able to maintain viable populations in the Faroe Islands.

There are also several endemic species of butterflies, and on hot summer days you can often see various loopers in flight across the infield. In October and right into December, you can encounter the small winter moth (Operophtera brumata). The females are wingless, and you can occasionally be lucky to see them sitting on poles and house walls while they wait for a winged male to come flying by.

Another eye-catching insect is froghopper (Philaenus spumarius), whose nymphs protect themselves from predators and drying out with a layer of foam, called cuckoo spit, while they suck on, for example, marshmarigold. The froghopper is a plant sucking insect together with ticks and aphids, of which 53 species are known from the Faroe Islands.

In addition to the insects, 194 different species of arachnids have also been recorded on the islands. Of these, the mites with 72 species and the spiders with 114 species make up the two largest groups. Among the spiders, however, it is probably only 90 species that have a permanent population on the islands. The most common spider is the orb-wheel spinner (Metellina merianae), which can be found in both infields and outfields. Wolf spider (Pirata piraticus) is also a frequent sight in the outfield where it lives in damp places in fens and along lakes and streams. It is able to run on the surface of the water and can catch its prey both above and below the water.

Further reading