Signs of SPIs
Identify common signs of Stored Product Insects
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Stored product insects (common species of beetles, weevils and moths in the UK) not only damage foodstuff and raw materials but can also contaminate finished products – making them unfit for use.
If you’re uncertain if you have an SPI problem or not, you can find all the signs to look out for here.
Learn the feeding habits and lifecycles of stored product insects and the damage they can do if left uncontrolled.
An approximate 3 – 4mm in length, adult confused flour beetles are a red-brown in colour and typically distinguished by antennas which broaden gradually at the tip. These insects possess the ability to fly but rarely do so. Their larvae are whitish to yellow-brown in colour, 1 – 5mm long in size.
Surviving approximately 20 days at 35°C and 45 days at 25°C, adults may live for up to 6 months in favourable conditions.
Confused flour beetles have a preference for clean flour, feeding on and pupating in flour and cereal products.
The red rust flour beetle has close set eyes, and the last three segments of their antennae form a club. Adults grow up to approximately 3 – 4mm in length and fly in warm climates.
Surviving approximately 20 days at 32.5°C and 45 days at 27.5°C, adults may live for up to 6 months in favourable conditions.
Feeds on cereals, nuts, spices and dried fruit.
Characterised by 6 saw-like projections on each side of the thorax, the saw toothed grain beetle has a long length of head behind the eyes. Adults grow to approximately 2.5 – 3mm in length and their larvae a yellow to brown in colour, with a brown head.
Surviving approximately 20 days at 35°C and 3 – 4 months at 20°C, the saw tooth grained beetle is comparatively more tolerant to temperature extremes than other pest beetles.
Feeds on cereal and cereal products, dried fruit, nuts etc.
The biscuit beetle has a humped thorax and a body covered in fine hairs, their wing cases have ridges with indentations. Adults grow to an approximate 2 – 3mm in length and larvae are known to be active in early stages of development.
Surviving approximately 70 days at 28°C and 200 days at 17°C, adults may live between 13 – 65 days in favourable conditions.
Biscuit beetles possess the ability to bore into hard substances and are able to detoxify some poisonous substances. Adults do not feed.
Black with a whitish band across the fore-part of the wing case, larder beetles are brown in colour and hairy. Larvae are distinguished by their comet shape, and these quick moving insects are known to migrate to pupate in solid material.
Larder beetles have a lifespan of approximately 2 – 3 months at 18 - 25°C.
Feeds on various animal products including cheese.
The size of booklice varies according to species, typically 1 -2 mm long, they range from a pale yellow-brown to dark brown in colour. Nymphs are very small and often appear transparent.
Booklice prefer high temperatures of 25 - 30°C but some species are known to breed at lower temperatures of 5 - 15°C.
Commonly found in homes and on pallets in factories.
With oval indentations in the thorax, grain weevils are black-brown in colour. Adults grow up to an approximate 2 – 3mm in length.
Surviving approximately 30 days at 30°C, grain weevils can live for up to 8 – 16 weeks in favourable conditions.
Feeds on grain, wheat, rye, cereal. Grain weevil larvae are usually hidden where they pupate, thus newly emerged adults leave an identifiable emergence hole in the grain.
Cigarette beetles have a humped thorax, smooth wing cases and adults grow to an approximate 2 – 3mm in length.
Surviving approximately 25 days at 30 - 35°C, cigarette beetles can live for 2 – 6 weeks in favourable conditions.
Possessing the ability to fly, the cigarette beetle feeds on a wide range of stored products including tobacco, cereal, pulses, dried fruit and spices.
With round indentations on the thorax and reddish spots on their wing cases, the rice weevil can grow up to an approximate 2 – 3mm in length.
Surviving approximately 98 days at 18°C, rice weevils can live for several months to a year in favourable conditions. Larvae will not develop below 16°C.
Feeds on grain and seeds. Rice weevil larvae are usually hidden where they pupate, thus newly emerged adults leave an identifiable emergence hole in the grain.
With 6 saw-like projections on each side of the thorax and a short length of head behind the eyes, merchant grain beetles grow up to an approximately 2.5 – 3mm in length, their larvae a yellow to brown in colour, with a black head.
Merchant grain beetles cannot tolerate low temperatures and thrive in optimum conditions of 30 – 33°C.
A particular pest of dried fruit and chocolate.
With a flattened, light red to dark reddish brown body, the flat grain beetle is characterised by a very long antennae and adults are an approximate 2.5mm in length. Adults are winged but rarely fly. Larvae are a yellow-white in colour, developing from 0.5mm to 4mm when mature.
The flat grain beetle prefers warm, damp conditions, surviving 69 – 103 days at 21°C and 26 days at 38°C.
Feeds on cereal, dates, dried fruit and other produce.
An approximate 3.5 – 4.5mm in length, male broadhorned beetles have two enlarged mandibles on the head, giving the appearance of horns and thus their name. Females are very similar In appearance to the confused flour beetle.
With temperature limits of 15 - 32°C, broadhorned flour beetles cannot complete their life cycle below 10°C.
Feeds on flour, dough, semolina etc. Moth eggs and larvae may supplement the broadhorned flour beetle diet.
Approximately 20mm long, yellow mealworm beetles are shiny, dark-brown or black. Larvae are a honey-yellow color with hard, highly polished worm-like body.
Highly resistant to cold temperatures, females lay about 275 – 600 white, bean-shaped eggs singly or in clusters during spring, which hatch into larvae in 4 – 14 days. The pupal stage lasts 7 – 24 days – first white, turning yellow (not enclosed in a cocoon) and finally emerging as adults with a lifespan of 2 – 3 months.
Adult yellow mealworm beetles are attracted to night-lights, and the strong fliers are commonly found in dark areas.
Covered in brown and golden hairs, the Australian spider beetle has a spider-life appearance and adults grow to an approximate 2.4 – 4mm in length.
Australian spider beetles live for up to 3 – 4 months at 20 - 25°C.
Larvae are often found feeding on miscellaneous debris, and the Australia spider beetle possesses the ability to bore into various inedible materials prior to pupation. Active in dark, damp places, the Australian spider beetle is often associated with bird nests.
Covered in golden-yellow hairs, the Golden spider beetle has an ovoid abdomen with a pinched waist and adults grow to approximately 2 – 4.5mm in length.
Surviving up 6 – 7 months at 20°C, the Golden spider beetle can live up to 9 months in favourable conditions.
Commonly linked to the damage of textiles in the domestic home, adults appear in greater numbers from June – July and October – November.
White or pale brown in colour, the slow moving flour mite can grow up to 0.5mm long. Larvae are white in colour and passes through two 8-legged nymphal stages.
Flour mites have a lifespan of 9 – 11 days at 23°C and 90% relative humidity.
Under adverse conditions, flour mites may pass through a long and very resistant stage called a hypopus.
Cheese mites have soft, hairy cream white bodies with 8 hairless legs and adults grow up to an approximate 0.5mm in length.
The cheese mite favours warm, moist conditions and eggs mature in 10 days at room temperatures. Females can lay up to 900 eggs in a lifetime at a rate of 20 – 30 a day. Adult cheese mites can live for up to 60 – 70 days.
With a preference for old cheese to young cheese, these mites also feed on nuts, dried eggs, fruit, flour and tobacco. Cheese mites are capable of contaminating foods to cause skin or gut irritation.
An approximate 7 – 9mm in length, the wingspan of an Indian meal moth develops to 15 – 20mm; the first third of forewings are a pale buff colour and the remainder of the winds are a reddish-brown. Larvae are a yellowish-white, reddish or greenish (depending on diet) with a brown head.
Surviving for 35 days at 35°C, the Indian meal moth lives for much longer at lower temperatures or when feeding on low nutrition foods.
Feeds on nuts, dried fruit and grain (maize)
Characterised by a black zig zag pattern across grey wings, the mill moth is an approximate 7 – 9mm in length with a wing span of 15 – 20mm. Larvae lives within a silken tube and have a pinkish or greenish tinge (depending on diet) with a brown head.
Surviving for 153 days at 17 and 42 days at 30°C, the prolific silk spinners can live for up to 2 weeks in favourable conditions.
A pest particular to flour, rarely feeds on other products.
Grey-brown banded with lighter and dark colours, tropical warehouse moths are an approximate 7 – 9mm in length with a wingspan of 15 – 20mm. Larvae are whitish, yellowish or reddish in colour (depending on diet) and tend to migrate to dark areas to pupate.
Tropical warehouse moths have a lifespan of 31 days at an optimum temperature of 32°C.
Often associated with imported food cargoes, the tropical warehouse moth is primarily a pest of stored cereal, nuts, dried fruit, oil seeds and oil cakes. Rarely feeds on tobacco and animal products. Adults do not feed.
An approximate 7 – 9mm in length with a wing span of 10 – 16mm, the warehouse moth is grey-brown banded with lighter and darker colours. Larvae are whitish, yellowish or reddish in colour (depending on diet) and tend to migrate to dark areas to pupate.
Eggs hatch from 3 -6 days above 20°C and pupae matures from 10 – 20 days over a temperature range of 18 - 26°C.
A formidable pest of cocoa beans, chocolate confectionary, dried fruit and nuts.