Household guests, named by DNA.

Fungus gnat

Sciaridae (incl. Bradysia sp.)

small, dark, mosquito-like

Damp potting soil and seedling trays. Flies slowly close to the soil surface and often arrives with new plants or bags of compost. The larvae eat algae and fungal threads but can damage the roots of young seedlings.

Tip: Let the top layer of soil dry out between waterings and remove withered leaves. A sticky trap catches the adults.

Sources: Hyönteismaailma · Anticimex.se: sorgmyggor

Fruit flies

Drosophila melanogaster etc.

adult 2–4 mm, larva 3 mm

Small, pale yellow-brown flies that swarm around spoiled fruit, kitchen waste, leftover beer and wine, jam and rotting potatoes. A female can lay up to 400 eggs and a generation develops in 10–14 days. Large numbers often come from the organic waste bin.

Tip: Remove spoiled fruit, keep fruit in bags and empty and clean the organic waste bin often.

Sources: Helsingin kaupunki: tuholaisesite · Hyönteismaailma · Anticimex.se: fruktflugor

House fly

Musca domestica

adult 6–8 mm, larva 10–12 mm

Flies into homes and breeds in compost, waste and livestock buildings. The thorax has four narrow dark stripes. The fly carries bacteria on its feet and mouthparts onto food and can spread stomach illnesses.

Tip: Non-toxic fly paper or a transparent window trap.

Sources: Hyönteismaailma · Anticimex.se: flugor

Blow flies (bluebottle and greenbottle)

Calliphora vomitoria, Lucilia etc.

9–13 mm and about 10 mm

The bluebottle is metallic blue and bristly, the greenbottle shiny green. They lay eggs on meat, fish and products made from them, and follow the smell of food from far away. In flight they buzz loudly.

Tip: Dispose of food waste and other breeding material carefully.

Sources: Hyönteismaailma · Anticimex.se: flugor

House spider (barn funnel weaver)

Tegenaria domestica

about 3 cm including legs

Dark brown and one of the most common indoor species. Spins its web in room corners, preferably in damp places. It is harmless and useful because it catches flies and other insects. No spider in Finland is a danger to people.

Tip: No control is needed.

Sources: Hyönteismaailma

Common harvestman

Phalangium opilio

3–9 mm, long thin legs

Not a spider. The body looks like a single part and the legs are long and slender. Lives on shady house walls, in cellars and outbuildings and often wanders indoors. It dies quickly in dry air. The harvestman eats harmful insects and mites.

Tip: Reduce moisture if harvestmen keep appearing indoors.

Sources: Hyönteismaailma · Anticimex.se: lockespindlar

Long-tailed silverfish

Ctenolepisma longicaudata

10–12 mm, up to about 18 mm

Wingless, silvery and matt, with three long bristles at the rear. Active at night. Spreads with furniture, clothes and bags, and moves through apartment blocks along pipe entries and gaps. Eats flour, food scraps, skin flakes, old books and textiles, among other things. Can live up to 8 years. It was first found in Denmark in 2017 and in Estonia in 2018 (Tartu), and it is spreading in northern Europe.

Tip: Seal cracks and gaps behind skirting boards. There are still few control methods, so an advanced infestation calls for a professional.

Sources: Hyönteismaailma · Anticimex.fi: paperitoukka · Videnskab.dk: skægkræ · Biodiversity Data Journal: Ctenolepisma longicaudatum, Viro

Reesa vespulae

2–4 mm, yellow spots at the base of the wing covers

Lives naturally in wasp and bee nests. Thrives in dry, warm centrally heated houses and eats dead insects, dry plant parts and seeds. Destroys insect and plant collections and seed stores.

Tip: Remove wasp nests from buildings and check collections and seed stores.

Sources: Hyönteismaailma · Helsingin kaupunki: tuholaisesite

Spider beetles and other uncommon beetles

Ptinus fur, P. tectus, Niptus hololeucus, Thylodrias contractus

Ptinus fur, Australian spider beetle, Niptus hololeucus, odd beetle

Rare in homes. Ptinus fur likes attics and cellars, the Australian spider beetle often arrives in imported goods, and Niptus hololeucus is spider-like and covered in golden-yellow hair. The odd beetle mostly harms insect collections.

Tip: Look for damp or rotting plant waste and clean attics, cellars and storage rooms.

Sources: Hyönteismaailma · Anticimex.se: tjuv- och mässingsbaggar

Pale mottled willow

Caradrina clavipalpis

wingspan about 3 cm

A noctuid moth with yellow-grey forewings crossed by black lines. The larva is grey-brown and about 2.5 cm long. In autumn both adults and larvae may come indoors to overwinter.

Tip: No control is needed. The larvae can be carried outside.

Sources: Hyönteismaailma

Common green lacewing

Chrysoperla carnea (syn. Anisochrysa carnea)

overwinters in homes

A harmless houseguest that overwinters indoors. In spring, individuals swarming inside can be let outside.

Tip: Release outdoors in spring.

Sources: Hyönteismaailma

Bee moth

Aphomia sociella

larvae live in nests, pupate indoors

Lives in the nests of bees, wasps and bumblebees. The larvae may move indoors to pupate and form a dense cluster that is hard to remove.

Tip: Remove wasp nests from buildings so the larvae cannot get in.

Sources: Hyönteismaailma

Common earwig

Forficula auricularia

about 2 cm

Dark brown, narrow and flat, with pincer-like appendages at the rear. Lives in gardens, moves at night and eats plants and fallen apples. Sometimes strays indoors but causes no damage.

Tip: Keep compost heaps away from the house.

Sources: Hyönteismaailma · Helsingin kaupunki: muut hyönteiset

Centipedes and millipedes

Chilopoda and Diplopoda

centipedes (Chilopoda) and millipedes (Diplopoda)

Centipedes have a flat body and one pair of legs on each segment. Millipedes have a cylindrical, hard body and two pairs of legs per segment. They come indoors with plants or looking for shelter and cause no damage.

Tip: Clear plant waste from around the house, pools and root cellars.

Sources: Hyönteismaailma · Anticimex.se: enkel- och dubbelfotingar

Two-spotted spider mite and strawberry mite

Tetranychus urticae and Phytonemus pallidus

under 0.5 mm and about 0.25 mm

Mites, not insects. The spider mite spins webs and sucks cell sap from the underside of leaves, and it likes dry, warm air. The strawberry mite damages developing leaves: young leaves turn brownish and the plant stays stunted. Hosts include strawberry and cyclamen.

Tip: A water spray or higher humidity, isolating the infested plant and good plant care.

Sources: Hyönteismaailma · Anticimex.se: kvalster

Common clothes moth

Tineola bisselliella

adult 9–16 mm, larva 10–12 mm

A glossy straw-yellow moth with a rust-brown head. The larva eats wool, fur and feathers and spins a tubular case from fibres and silk. Holes in fabric and pupal cases give the moths away.

Tip: Air, shake and vacuum wardrobes. Wash textiles at 40–60 °C or freeze them for a week at −20 °C.

Sources: Helsingin kaupunki: tuholaisesite · Martat: tekstiilituholaiset ja lutikat · Anticimex.se: mal

Indian meal moth

Plodia interpunctella

adult 14–20 mm, larva about 10 mm

The base of the forewings is yellow-grey and the tips strongly rust-red, and the head is rust-red. The larva is grey, slightly translucent and brown-headed. Contaminates dry foods such as crispbread, flour, spices and biscuits, and usually arrives in shop packaging.

Tip: Check dry goods, including unopened packs, discard infested items and store food in glass or plastic containers. A suspect product can be frozen for a week.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: skafferiskadegörare

Fur beetles

Attagenus woodroffei, Attagenus pellio

adult 4–6 mm, larva 10–11 mm

The banded fur beetle is dark brown with a broad yellowish wavy band across the back. The two-spotted fur beetle has two silver-grey spots on the back. The larvae are brown and cross-banded with a tuft of hair at the rear. They eat wool, fur, hides and stored grain.

Tip: Check storage spaces, vacuum and dispose of the bag. Wash at 40–60 °C or freeze for a week at −20 °C.

Sources: Helsingin kaupunki: tuholaisesite · Rentokil.dk: tekstilskadedyr · Anticimex.se: pälsängrar

Carpet beetles

Anthrenus museorum, A. verbasci, A. scrophulariae, A. olgae

adult 1.5–4 mm, larva 4–5 mm

A roundish, patterned beetle. The museum beetle (A. museorum) is almost spherical, black with grey and yellow-brown patches. Adults visit flowers and fly in through windows. The damage is done by the hairy larva with a tuft at the rear: it eats wool, feathers and dead insects and makes small holes in fabric.

Tip: Check lamps, windowsills and hiding places under sofas. Vacuum, wash textiles at 60 °C or freeze for a week at −20 °C.

Sources: Helsingin kaupunki: tuholaisesite · Rödceder: mattbaggar · Martat: tekstiilituholaiset ja lutikat

Larder beetle and other Dermestes beetles

Dermestes lardarius, D. maculatus

adult 6–10 mm, larva 12–16 mm

The larder beetle is dark grey with a broad pale grey band, carrying three small dark spots, at the base of the wing covers. The larva is dark, hairy and banded, with two small curved spines at the rear. A Danish source also lists Dermestes maculatus, which eats animal material: hide, feathers, hair and dried fish.

Tip: Remove animal-based food such as dried meat and fish and vacuum thoroughly. Wash textiles at 60 °C or freeze for a week.

Sources: Helsingin kaupunki: tuholaisesite · Rentokil.dk: tekstilskadedyr · Anticimex.se: fläskängrar

Sawtoothed grain beetle

Oryzaephilus surinamensis

adult 2.5–3.5 mm, larva 3 mm

A brown, elongated beetle with saw-toothed sides on the thorax. The larva is pale and almost hairless. Contaminates dry foods such as crispbread, flour, spices and biscuits, and usually arrives in shop packaging. The food is rarely poisonous but is spoiled.

Tip: Check dry goods, discard infested items, empty and vacuum cupboards. Report the find to the shop where the product was bought.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: skafferiskadegörare

Flour beetles (Tribolium)

Tribolium destructor, Tribolium confusum

5–6 mm and 3–4 mm

Tribolium destructor is black or dark brown. The larva is shiny yellow-brown with two upward-curving spines at the rear. Its foul-smelling, foul-tasting secretion makes food inedible. The confused flour beetle is reddish brown, smaller and resembles it.

Tip: Check flour and other dry goods, discard infested items and store food in glass or plastic containers.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: mjölbaggar

Yellow mealworm beetle

Tenebrio molitor

adult 12–16 mm, larva about 30 mm

A black or dark brown beetle that resembles the flour beetle but is larger. The larva is shiny yellow-brown and sturdy with two small spines at the rear. Lives in rotting wood and bird and wasp nests, from where it enters homes and eats food.

Tip: Look for a possible nest near the building and discard infested food.

Sources: Helsingin kaupunki: tuholaisesite

Drugstore beetle

Stegobium paniceum

adult 3 mm, larva 3 mm

A small, rust-brown, densely hairy beetle. The larva is pale with a curved rear end. Eats dry foods and usually arrives in shop packaging. A Swedish source treats bread beetles and tobacco beetles together because they resemble each other.

Tip: Check dry goods, empty and vacuum cupboards and store food in sealed containers.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: bröd- och tobaksbaggar

German cockroach

Blattella germanica

adult 8–13 mm

Yellowish brown with two dark brown stripes on the thorax. The wings fully cover the abdomen and the antennae are long and thread-like. Nymphs resemble adults but have short wing pads. May spread salmonella.

Tip: Keep food in sealed containers and clean up food scraps. Report the find to the property manager or maintenance company.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: kackerlackor

Common silverfish

Lepisma saccharinum

about 12 mm

Wingless, elongated and silvery, with three long bristles at the rear. Active at night and likes damp rooms such as kitchens, bathrooms and areas near floor drains. Eats paper, wallpaper paste and fungi. Large numbers can point to moisture damage.

Tip: Keep damp rooms dry and ventilated, clean floor drains and seal pipe entries.

Sources: Helsingin kaupunki: tuholaisesite · Helsingin kaupunki: muut hyönteiset · Anticimex.se: silverfiskar

Ghost silverfish and relatives

Ctenolepisma calvum, C. lineatum, Thermobia domestica

Thermobia about 2 cm

The ghost silverfish (C. calvum) has been reported spreading to museums and homes in Europe. A Danish source also names C. lineatum, larger than the common silverfish and found indoors near food and dust, and Thermobia domestica, a heat-loving firebrat that is grey with dark spots.

Tip: Keep moisture and food under control and seal gaps. Report an unfamiliar species to an expert.

Sources: Rentokil.dk: sølvfisk · Aarhus Univ.: sølvkræ · Insects 2022: Ctenolepisma calvum

Black garden ant and carpenter ant

Lasius niger, Camponotus herculeanus

black garden ant about 4–5 mm

The black garden ant is black and the most common ant found indoors in Finland. The nest is usually in soil or under stones, and ants visit homes in spring and summer looking for food. The harm stays minor unless the nest is in the building structure.

Tip: Find the entry point by following the ant trail, discard contaminated food and seal the rest. A nest in the structure needs an expert.

Sources: Helsingin kaupunki: tuholaisesite · Helsingin kaupunki: muut hyönteiset · Anticimex.se: hästmyror

Pharaoh ant

Monomorium pharaonis

1.5–2 mm

Yellowish and tiny, so it is hard to spot. Thrives in warm, humid places with food and water, and there are often many nests. Originally from tropical Africa. Can short-circuit electronics and spreads from building to building along district heating ducts.

Tip: Control requires a professional.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: faraomyror

Bed bug

Cimex lectularius

5–8 mm

A broad, flat, brownish blood-feeding bug. A hungry individual is pale. Hides by day in mattress seams, bed frame crevices, behind wallpaper and in sockets. Signs are blood stains and black faecal spots on sheets and itchy welts.

Tip: Control needs a professional, so report it to the property manager at once. Wash bedding at 60 °C or freeze for a week at −18 °C. Do not use consumer pesticides.

Sources: Helsingin kaupunki: tuholaisesite · Martat: tekstiilituholaiset ja lutikat · Anticimex.se: vägglöss

Head louse and body louse

Pediculus humanus

head louse 2.5–3 mm

The head louse is wingless, flat, white or grey, lives only in hair and glues its nits to the base of hairs. It is not known to spread disease. The body louse lives in clothing and can spread disease.

Tip: Head lice are treated with pharmacy products and bedding is washed at 60 °C. For body lice, contact a health centre.

Sources: Helsingin kaupunki: tuholaisesite · Anticimex.se: löss

Fleas

Siphonaptera (incl. Pulex irritans)

1–6 mm

Shiny, wingless and usually dark, flattened from side to side and strong jumpers. The larva is white and legless. They live in the nests of mammals and birds. Denmark has 45 species, including hedgehog, bird, dog and cat fleas.

Tip: Control needs a professional. Vacuum the mattress and bed, wash bedding at 60 °C and notify the property manager.

Sources: Helsingin kaupunki: tuholaisesite · Rentokil.dk: skadedyr i hjemmet · Anticimex.se: loppor

Booklice (psocids)

Psocoptera

1–4 mm

Greyish white or brown, thin-skinned and almost translucent. They run jerkily and seem to hop, and are often mistaken for bed bug nymphs. Common in attics, cellars, dust, old books and cardboard boxes. They eat mould spores, so their presence points to humidity.

Tip: Keep indoor humidity at or below 50 % and clean dry without wet mopping.

Sources: Helsingin kaupunki: muut hyönteiset · Anticimex.se: damm- och boklöss

Springtails

Collembola

up to 6 mm

Small, round or elongated, with a forked jumping organ under the abdomen. Sweden has 170 known species. Most live in vegetation, soil and rotting wood. They show up in houseplant pots because they feed on decaying plant matter and fungal threads. Harm to seedlings is rare.

Tip: Let the surface of the pot soil dry out.

Sources: Helsingin kaupunki: muut hyönteiset · Anticimex.se: hoppstjärtar

Woodlice

Oniscus asellus, Porcellio scaber

up to 18 mm

Not insects but crustaceans. Flat, oval and armoured, with seven pairs of legs. The common woodlouse and the rough woodlouse live in damp places and eat decaying plant matter. Sometimes stray into cellars. Not pests except in sensitive places such as commercial kitchens. They dry out easily.

Tip: Reduce moisture and clear rotting plant matter around the cellar.

Sources: Helsingin kaupunki: muut hyönteiset · Anticimex.se: gråsuggor

House longhorn beetle

Hylotrupes bajulus

exit hole 5–8 mm

The larva lives inside the wood and bores winding galleries. Signs are oval exit holes and pale boring dust. Attacks only softwood, pine and spruce, often roof trusses in attics. Sweden's most notable wood-boring insect, which can destroy entire houses.

Tip: If you suspect an infestation, order a professional inspection.

Sources: Anticimex.se: husbock

Common furniture beetle

Anobium punctatum

2–4 mm, exit hole about 2 mm

A small brown beetle whose larvae damage wood. Signs are round exit holes and fine boring dust. Likes damp wood, often in unheated buildings such as holiday homes and churches. Can also attack damp-stored books and paper.

Tip: Dry the wood, since dry wood prevents new infestations. Small items can be frozen for at least a week.

Sources: Anticimex.se: strimmig trägnagare

Moth flies (drain flies)

Psychodidae (incl. Clogmia albipunctata)

small fly

Small, hairy flies. They lay eggs in floor drains, sewer pipes and water traps, where the larvae and pupae develop. Adults are drawn to light and sit on windows. They do not bite or damage anything but are a nuisance in large numbers.

Tip: Clean rarely used floor drains and water traps.

Sources: Anticimex.se: fjärilsmygga

Cluster flies

Pollenia

fly, autumn overwinterer

They seek shelter indoors in autumn to overwinter. The larvae live outdoors in the soil and eat earthworms. They do not harm people or property, but large numbers are a nuisance.

Tip: Seal gaps, fit fine mesh to vents and windows and vacuum up flies that get in.

Sources: Anticimex.se: vindsflugor

Bird mites

Dermanyssus gallinae etc.

tiny mites

They normally live among birds' feathers. When the host birds are gone, for example from an abandoned nest, the mites may spread into a home. They feed on blood and the bites can cause an irritating rash.

Tip: Look for nearby birds and nests, remove or clean abandoned nests and call a professional for a severe case.

Sources: Anticimex.se: fågelkvalster