About invertebrates in Scotland


Internationally important

Scotland’s rivers are home to internationally important populations of freshwater pearl mussels. These mussels can live for over 100 years, if they are not killed, illegally, by someone with the slim hope of finding a pearl.

The historic pine woods of the Highlands are home to many rare and threatened species including the pine hoverfly which lays its eggs in old pine stumps.


Flower-rich machair grassland in northwest Scotland supports populations of the great yellow bumblebee and the northern colletes bee. The marsh fritillary butterfly is declining across Europe and wet meadows in western Scotland managed in traditional ways are one of the most important remaining areas for this species.

Nature needs them

Invertebrates are vitally important to us. They turn natural waste into fertile soil and pollinate our crops and flowers. They are an essential food source for wild animals and birds; a single bird species, the blue tit, feeds it chicks with approximately one billion caterpillars and other small invertebrates every year.

We need them

Many smaller invertebrates also have important roles in the food-chain, occurring in large numbers and concentrations that nourish many fish and whale species, from tiny sandeels to giant basking sharks and humpback whales. Invertebrates which attach to the seabed and live in large colonies also form some of the most important marine habitats, supporting a diverse range of other marine organisms.

What SNH is doing


Scottish Natural Heritage (SNH) helps to protect invertebrates by including them in the Species Action Framework and by looking after designated sites. SNH works with and funds other organisations to provide information, events and research into the best ways to protect all our wildlife. SNH also recently supported the development of a strategy for the conservation of Scottish invertebrates  .  Some invertebrates have legal protection because their future is so precarious. 

What you can do

Many invertebrates are threatened by the loss and break up of their habitats or a decline in habitat quality. Others are at risk from climate change or pollution. To find out more about how you can help invertebrates, follow the links to the organisations listed on the species pages..

Freshwater invertebrates

The invertebrates that live in our lochs and burns are diverse and play a vital role in maintaining the quality of our water. They help with the breakdown of organic debris and are a food source for other species such as fish, birds and bats.

Dragonflies and damselflies

The order Odonata comprises dragonflies (wings outstretched at rest) and damselflies (wings folded at rest). They are an ancient group, having arisen in the Carboniferous Period (300 million years ago). This is 150 million years before the first birds, and 295 million years before man appeared on Earth.


They are mainly tropical insects with over 5,000 species worldwide. Europe has about 114 breeding species, the British Isles 38 and Scotland 21. In Scotland, the commonest species breed in ponds and lochans. These water bodies are quite widespread but vulnerable to drainage, pollution and infilling.

The adults feed on live insects which they catch while in flight, particularly midges and mosquitoes. They also will take butterflies, moths and smaller dragonflies. The adults frequent sheltered, sunny glades where prey is plentiful. Eggs are deposited in, or near, fresh water or into aquatic vegetation.


The larvae prey on a variety of aquatic organisms and moult several times over a period of months, or years depending on species.

How you can help

Dragonflies are attractive and just about as easy to identify as birds.  We are very short of dragonfly recorders in Scotland so if you live here or are just visiting on holiday, please do send in your dragonfly records to the British Dragonfly Society to help us determine the health of our dragonfly populations. 

Freshwater pearl mussel

The freshwater pearl mussel is an important part of our biodiversity and has an important place in our cultural heritage. However the species is one of the most critically endangered molluscs in the world. Part of the reason pearl mussels are rare in Scotland is due to ongoing, illegal pearl fishing and they need your help.

Freshwater pearl mussel

Scotland contains many of the world’s most important remaining populations. But even in Scotland there has been a dramatic decline in the number of rivers that continue to support freshwater pearl mussels. Over the last 100 years more than one third of the rivers that used to contain freshwater pearl mussels no longer do so. A further third only contain old freshwater pearl mussels, with no sign of reproduction. They are witness to our rivers’ deteriorating status and need urgent conservation action .

What can I do to help?

To help counter criminal threats the pearl mussel very much needs your help. If you see any suspicious activity in or near a river that may contain pearl mussels, please contact the police  as soon as possible. Further information about how to help is available in a leaflet   . If you are planning to work in a river that may contain pearl mussels, please be aware it is a crime to damage pearl mussels. 

What are freshwater pearl mussels?

Freshwater pearl mussels are similar in shape to common marine mussels but grow much larger and live far longer than their marine relatives. Incredibly, they can live for more than 100 years, making them one of the longest-lived invertebrates. They can grow to as large as your hand and are dark brown to black in colour. They live at the bottom of clean, fast-flowing rivers, where they can be completely or partly buried in course sand or fine gravel. They feed by drawing in river water and filtering out fine particles. Each day an adult is able to filter more water than we use in an average shower.  They have a complex lifecycle and, in their first year, they harmlessly live on the gills of young salmon or trout.

Why are they endangered?

Their place in our history comes from the fact that they very occasionally bear a pearl. In some ways this has led to their downfall, with over-exploitation by ‘pearl-fishers’ primarily responsible for massive declines in their numbers and range. But as filter feeders, freshwater pearl mussels are also extremely vulnerable to water pollution and engineering work in rivers such as the construction of weirs or deepening of pools. The effect of these threats means that the survival of the species in Scotland is not assured. As such, the freshwater pearl mussel is fully protected  making it illegal to disturb, injure, take or kill a freshwater pearl mussel. Despite this protection, the threat continues and the freshwater pearl mussel is a UK wildlife crime conservation priority.

Their place in our cultural heritage

Exploitation of freshwater pearl mussels has taken place since pre-Roman times. The earliest reference in Britain is by Julius Caesar’s biographer, Suetonius, who stated that Caeser’s admiration of pearls was a reason for the first Roman invasion in 55BC. In Scotland, the earliest reference dates back to the 12th Century when Alexander I, King of Scots was said to have the best pearl collection of any man living. The medieval poem ‘The Parl’ which dates from the late 14th Century is another early reference to freshwater pearl mussels in Scotland.

Freshwater pearl mussel

There are further references in later centuries that indicate a growing exploitation of Scottish pearl mussels. By the 18th century the first references to a decline in pearl mussel numbers can be seen. This decline accelerated during the 20th century, such that more recently there was evidence that pearl mussels became extinct from an average of two rivers every year in Scotland between 1970 and 1998 (when the species gained full legal protection).

Given the freshwater pearl mussel’s place in our cultural history it is important that the final chapter in that history is not to see the species become extinct in our rivers. Rather, with action, its history will remain alongside its continued place as an important component of our biodiversity.

Stoneflies, mayflies and caddisflies – river flies

This category includes several groups of insects which spend most of their lives as larvae on the beds of our rivers and lochs. They are an essential part of this environment providing a food supply for fish and birds such as the dipper.

Mayflies are some of the oldest winged insects known dating from over 300 million years ago. There are around 3050 species known from the World. Mayflies are the only insects to have two winged adult stages. 51 species know from the British Isles.


Stoneflies are a small group of aquatic insects, which generally prefer stony, fast flowing streams. There are 34 British species, including one species, the Northern February red (Brachyptera putata) which is only found in Scottish watercourses.

The Trichoptera, or Caddisflies, are an order of insects, which resemble moths, and of which there are just under 200 species in the British Isles. The name means ‘hairy-winged’, and indeed they differ from moths in having hairs rather than scales on their wings, amongst other differences.

Riverflies are vulnerable to pollution but Scotland has a high proportion of very clean waters. 

Marine invertebrates

Land based (terrestrial) invertebrates

Invertebrates (especially insects) are everywhere and in very large numbers. They are essential in recycling dead material and in the pollination of flowering plants. They form one of the primary steps in the food chain, and many of our mammals and birds depend on them as food to some degree.

The health of the environment and the very survival of humans depend on invertebrates, and for those reasons the biologist Edward O. Wilson called them “the little things that rule the world”.

There are at least 14,000 species of insects in Scotland, not including all the other invertebrate groups such as spiders, worms, slugs and snails, crabs and lobsters. A number of our species occur nowhere else in the world, these are known as endemic species.

Scotland is unique within the British isles in having a large proportions of boreal (northern or Scandinavian) insect species that are associated with our mountains, peatlands and native woodlands of pine, aspen and birch. In many aspects Highland insects in particular show greater affinity to those in countries such as Norway and Sweden rather than with other parts of the British isles.

Some species are naturally scarce, but many have became rare because of habitat loss or fragmentation. The diversity of invertebrates on agricultural land has been greatly affected by modern agricultural techniques.

Bees, wasps and ants

Hymenoptera are the “membrane-winged” insects, one of the most diverse groups of animals. Their largest family, Ichneumonidae, includes more species than those of all birds and mammals combined. There are more than 6,500 species in Britain, comprising almost 30% of the total insect fauna.


Many species have developed social systems in which members are divided into workers, drones and queens. These social hymenoptera may live together in nests or hives of many thousands of individuals. But not all species are social; many live a solitary life, coming together only for a brief mating. Hymenoptera are invaluable for their services in pollination and pest control.

Some important Hymenoptera species or groups include:

  • wood ants  
  • bumblebees  
  • mason bees  
  • northern colletes bee  
  • wasps  


Beetles belong to the Order Coleoptera (sheath-winged, a reference to their hardened forewings), range in size from 0.25 mm to over 17 cm, and occur practically everywhere.

Beetles are the largest group of insects, with approximately 400,000 species described across the world. This number means that 1 in 4 of all known animal species is a beetle. Hence the quote, ascribed to the British geneticist J. B. S. Haldane, that the Creator has, or had, an inordinate fondness for beetles.  There are about 4,000 species from the British Isles. Of these, about two thirds, or between 2,500 and 3,000, occur in Scotland. However, most of Scotland remains poorly surveyed and our knowledge of the beetle fauna as a whole is patchy and incomplete.


Many beetles are important pollinators, while dung beetles (especially (scarabs) remove vast quantities of dung from the environment. Carabid beetles help reduce the number of plant-eating caterpillars and slugs. The simplification of our arable ecosystems has reduced the number of such predators in our fields and strips of grass may be deliberately left in fields as beetle banks. Other beetles, such as the heather beetle and the harlequin ladybird, can be harmful under certain circumstances.

In Scotland, some species are of special conservation concern, such as the ten-spotted pot beetle, the six-spotted pot beetle, the water beetle Hydroporus rufifrons and the reed beetle Donacia aquatica.

Butterflies and moths

If you can identify birds, you can identify the butterflies which are readily recognised by their colourful wing patterns. Moths are less known because they generally fly by night but they are much more diverse and include some species that are even more striking than our butterflies.  There are about 34 species of butterfly seen regularly in Scotland but about 1,300 species of moth.

Butterflies and moths

Some moths do fly by day – look out for the striking red and black burnet moths in grassland that still has a good range of flowers, especially by the sea. Their colour has a reason, it is to warn predators that they are poisonous – so that is why they can fly by day. 

Technology can help to bring moths to your garden for you to look at and identify – moth traps do not harm the moths but lure them in with light.  If you try this, do send in your observations to Moths Count (see ‘how you can help’ below).

Threats to butterflies and moths

There have been large changes in the way we manage the countryside over the past 50 years and we know that butterflies and moths have suffered as a result.  Butterflies have been divided into generalists that are continuing to do well and specialists, such as the chequered skipper, the marsh fritillary and the pearl-bordered fritillary, that are becoming increasingly rare as their habitats are being reduced or altered. The indicator of trends in Scottish butterflies   suggests that about 48% of our specialist butterflies declined since 1967. 

Moths are also affected in the same way: the once familiar garden tiger moth, for instance, is believed to have declined by 90% in the UK since 1960.  The indicator of trends in Scottish moths   suggests that the proportion of species declining in Scotland is very similar to that in Britain as a whole (21%) but that we have a higher proportion of increasing species (45%).  

How you can help

Butterfly Conservation Scotland involve their members, and others, in the monitoring and management of threatened butterflies and moths.  Recent actions have taken place to protect the marsh fritillary butterfly, the slender scotch burnet moth and the dark bordered beauty moth.  In addition Butterfly Conservation run the important national monitoring schemes for butterflies and moths  which depend on volunteers like you. 

Never underestimate the power of the volunteer.  One of Scotland’s greatest conservation successes, the saving of the New Forest Burnet Moth (no longer known in the New Forest but still found on one site in Scotland) was lead by a committee of experts who voluntarily gave their time to work closely with Scottish Natural Heritage on this species.


Although beetles are the dominant insect group worldwide, flies (Order Diptera, meaning “two wings”) are more abundant in temperate regions. In the British Isles, there are about 7,000 species.

The young stages of flies – the larvae – are commonly found in the soil, water, plants, carrion, dung, dead wood – mostly places with high levels of moisture. Many are nectar feeders and play an important role as pollinators. That’s the case of hoverflies; they are familiar garden visitors. Others feed on decaying matter and are important for recycling dung and dead animals.


Some species of Diptera, represent serious health problems.  Mosquitoes can transmit deadly diseases, including yellow fever, malaria and sleeping sickness. In Scotland, midges can be a major nuisance because of their numbers in the summer months, but they are an important part of the food chain

Scotland is home of two hoverflies of special interest because of their rarity and the conservation efforts put together to protect them; they are the aspen hoverfly and the pine hoverfly. Other important species in Scotland are the craneflies Scottish yellow splinter and the Northern yellow Splinter, and the stiletto fly Spiriverpa lunulata.

Slugs and Snails (Molluscs)

Molluscs are soft-bodied invertebrates without internal skeletons, although most of them have shells that support and protect their bodies. Molluscs comprise bivalves (clams and mussels) and gastropods (snails and slugs). Gastropod means “belly feet”, a reference to the way they move by creeping on their undersides (“bellies”).


Slugs have evolved from snails through the reduction or loss of their shell. Lacking a convenient shell to hide in when times get tough, slugs are more susceptible to desiccation than snails, although they protect themselves to some extent with mucus.

Slugs and snails are usually seen as pests in the garden, although most of them prefer to eat decaying plant matter. This means that tidy gardens are likely to suffer more damage than those that have dead vegetation around. However, transfer your molluscs to the compost bin and they will do you a great service there. 

There are about 24 British slug species, and about half of these turn up in the garden from time to time. A mature garden can have an interesting range of snails to try to identify too. Thrushes, frogs, toads, slow-worms, shrews and hedgehogs all feed on snails and slugs.


Different groups can be distinguished from each other by their ways of locomotion. Earthworms wriggle and use bristles along their body, flatworms slowly glide with the aid of tiny cilia (hair-like structures) and nematodes (roundworms) move franticly in S-shaped curves. Some worms keep the soil healthy, others attack plants in the garden, and one, the medicinal leech, can be used as an aid on the surgery table…

There are over 3,000 kinds of earthworm in the world. Most of them tunnel burrow in tunnels that allow air to penetrate the soil. Charles Darwin found that by this methodical work, worms could bury the equivalent of a football pitch in 15 tonnes of soil a year from the casts they leave on the surface.


Nematodes or roundworms can be found mostly in ponds, but many species are soil dwellers or live as parasite in other organisms. They form an important role in the breakdown of organic matter in soil and the bottom of ponds.

Flatworms are simple animals, often found in damp places. They are mostly scavengers or predators. Freshwater flatworms live in many aquatic habitats, from running water to ponds and lakes. The New Zealand flatworm occurs predominantly in gardens, where it feeds exclusively on earthworms. There is still concern about its likely impact on earthworm populations in Britain as earthworms are an important prey item for many animals including badgers, buzzards and the blackbirds on your lawn but most importantly they are so important in maintaining the fertility of the soil.

Spiders, harvestmen, mites and ticks

Spiders, harvestmen, pseudo-scorpions, ticks and mites belong to a group of invertebrates called arachnids. One of the most evident differences between insects and arachnids is the number of legs: insects have six legs, arachnids have eight.

Spiders make up the majority of the group, with over 50,000 known species. Almost all spiders are predators, and in turn are eaten by lizards, slow-worms and by many birds and small mammals. Scotland is a special place for mountain spiders which live under the stones on our highest mountains and for a few species that live in our native pinewoods.


Harvestmen, which superficially resemble spiders, are also predators of other animals including slugs, snails, woodlice, millipedes, centipedes – and spiders. Among the creatures that eat harvestmen are some birds, common lizards, beetles, centipedes and hedgehogs. However, harvestmen are able to produce a secretion from glands on their body which evidently deters some potential predators such as blue tits and house sparrows.

The first spiders and harvestmen  that look just like those we see today are found as fossils as far back as the early Devonian period – more than 400 million years ago.  The dinosaurs arrived about 170 million years later. 

Other groups

Many more invertebrates are part of the Scottish fauna, some very abundant but little known because they are small, others often overlooked because they live underground or hidden behind a tree bark or among foliage. These include:

  • Millipedes and Centipedes (Myriapods)
  • Woodlice and Waterlice (Isopods)
  • Bristletails (Thysanura and Diplura)
  • Springtails (Collembola)
  • Lice (Mallophaga and Anoplura)
  • Grasshoppers (Orthoptera)
  • True bugs (Hemiptera)
  • Earwigs (Dermaptera)
  • Lacewings, alderflies and Snake flies (Neuroptera)  

Never underestimate the invertebrates, they make up nearly all of the animal life in Scotland.  And they have been here a long time.  There are fossil myriapod (giant centipede) tracks in Scotland on Arran, at Crail in Fife  and on Skye.  Those in Fife date from the lower Carboniferous period about 350 million years ago.  The Rhynie Chert  , found near the Scottish village of Rhynie, is one of world’s most exciting fossil beds of the first plants about 410 million years old.  It has springtails (and mites) like those found in decaying leaves today in modern woods. 

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