An important service provided by invertebrates is waste recycling - making minerals and organic material available again to plants and other animals. In the soil earthworms and other invertebrates play crucial roles in the decomposition of organic matter. Their activities improve the drainage, aeration and composition of the soil, thus enabling plant growth. The decomposition of dead plants and animals including dung and fallen wood relies upon invertebrates.
|Hibernating earthworm © Roger Key|
Basis of ecosystems
Most marine habitats are dominated by invertebrates. In some cases, such as Flameshell reefs (Limaria hians) and Northern sea fan (Swiftia pallida) and sponge communities, the entire habitat is based on invertebrates. Birds and fish rely on these invertebrates for food and the abundance and diversity of marine plankton is a useful indicator of healthy marine ecosystems.
Many plants rely on insects to pollinate their flowers and so complete their reproductive cycle. Well-known pollinators include bumblebees, honeybees, butterflies and hoverflies, less well known ones include moths, thrips, beetles and solitary bees.
|Hive bee © Alan Stubbs|
Invertebrates form the basis of numerous food chains. Many birds feed on invertebrates, whether as food for their chicks or as part of their adult diet. Migrant birds such as swallows, swifts and martins travel long distances to feed on insects in the British Isles. The chicks of Blue tits eat an estimated 35 billion caterpillars and other small invertebrates every year. A number of uplands birds, such as Golden plovers and Greenshanks time their breeding to coincide with the emergence of craneflies, which form the majority of the diet of their chicks. Baleen whales such as the Minke whale and many seabirds feed extensively on Krill (Euphausia superba) and other marine crustaceans. The diet of Puffins primarily consists of Sand eels, which in turn feed upon planktonic species of crustacean and other invertebrates. Mammals such as bats, badgers, voles and shrews also feed on invertebrates. It is estimated that a single Pipistrelle bat will consume over 3,000 small insects every night. In freshwater ecosystems the diet of game fish such as the Atlantic salmon and Brown/Sea trout is comprised entirely of aquatic invertebrates. Birds such as the Dipper and Grey Wagtail also depend upon aquatic invertebrates in our rivers and streams.
There is a long history of invertebrates being used as indicators of the health of our environment. In determining the quality of our rivers and lochs, the Scottish Environment Protection Agency routinely use assessments of the number and variety of aquatic invertebrates alongside chemical analyses. Invertebrates are also used to test the toxicity of chemicals such as pesticides.
Assessing habitat quality
Since 1979 the UK butterfly monitoring scheme has been recording trends in butterfly species. The information gathered plays an important role in assessing habitat diversity, habitat fragmentation and the impacts of climate and other environmental change. Through the Rothamsted light-trap network, which started in 1965, we know that about two-thirds of moth species are declining, and about 20% of all species are declining sharply.
|Chequered skipper © Martin Warren|
The Scottish Agricultural Science Agency monitors aphid populations as part of the Rothamsted suction trap network which has been in operation since 1965. The information from this network is used to study the factors affecting the dynamics of aphid populations and to guide aphid control decisions.
In agricultural systems, simple measures such as conserving headlands and making ‘beetle banks’ encourage predatory invertebrates such as beetles and hoverflies, which not only help to control pests but also provide additional food for birds and mammals.
In addition, pests can be individually targeted with specific invertebrate enemies like native ladybirds and parasitoid wasps. Increasingly these are available commercially and they may offer an environmentally friendly option to chemical control.