Invertebrates are animals without a backbone, such as insects, spiders, worms, slugs, snails and centipedes.
Virtually unseen to the untrained eye, invertebrates are vital components of a bush ecosystem.
What do they do?
They can be:
- Pollinators e.g. bees and butterflies.
- Herbivores e.g.stick insects.
- Predators e.g. spiders, praying mantis.
- Parasites e.g. ticks and lice.
- Detritivores i.e. breaking down leaf litter and other organic matter e.g. worms.
- Food for reptiles, birds, mammals and other invertebrates!.
Where do they live?
Look out for invertebrates living in the soil, leaf litter, forest understory and high in the canopy. Many shelter under logs and stones. Take a torch and explore the bush at night, as this is an active time for many bugs. Each has an important role to play in the overall functioning of the bush.
Standing in a forest, many visitors are surprised to learn that most of the animal life around them lies under their feet! The majority of invertebrates living in the bush are found in the leaf litter or underground, including earthworms and the larvae of insects such as beetles, moths and cicadas.
Worms are natural ‘mulchers’ and ‘composters’, maintaining soil health by eating the decaying remains of plants and animals from the soil surface. The nutrient-rich worm casts (waste material) are deposited around the roots of plants as they make their way through the soil. In effect, worms are fertilising plants as they move and feed. The burrowing holes of worms also aerate the soil and allow plant roots to penetrate more easily.
Leaf litter bugs
Without the industrious actions of leaf decomposers, forests would drown under piles of their own leaves. Decomposers such as litter hoppers, springtails and ground weta play a vital role in breaking down vegetative matter and returning nutrients to the soil.
Under log and stone bugs
Predatory beetles, spiders and centipedes hang out under logs and stones during the day and come out at night to hunt.
Many insects feed on leaves, twigs and branches of the forest understory and inflict little damage on the plants themselves. The caterpillar of New Zealand’s largest moth – the puriri moth - for example, makes tunnels in the trunk of the puriri tree that are shaped like a ‘7’. They feed on the wood for about three years before emerging. Weta often shelter in the vacant holes left by the caterpillar.
High flying bugs
High in the forest canopy bees, flies, beetles and night-flying moths feed on the nectar of flowering plants and trees. They play a vital role in pollinating many of our native plants, which have evolved small, simple flowers that can be pollinated by a variety of species, such as our native short-tongued, solitary bees.
Other insects that feed in the forest canopy include stick insects, caterpillars, weevils and scale insects.
General indicators of forest health
The table below gives key indicators for assessing forest health using invertebrates:
|Healthy forest||Unhealthy forest|
Look for the following 'indicator' bugs:
Weta, observe feeding at night.
Litter hoppers, in leaf litter.
|'Indicator' bugs absent.|
|Insect calls can be heard at night, e.g. weta make a rasping sound at night.||The forest is silent at night.|
|Insects, such as cicada, can be heard during the day.||The forest is silent during the day.|
|Leaf litter layer is thick with bugs visible when leaves disturbed.||Leaf litter layer is thin, with few or no bugs.|
|High proportion of native invertebrates.||High proportion of introduced invertebrates e.g. garden snail.|
|Pollinator species are present e.g. bees and butterflies.||Pollinator species are absent, result in slower regeneration of the forest.|
You may need to check several times for bugs as numbers present can vary depending on the time of year and temperature. You are not likely to find many flying insects in winter.
What you can do?
Small and often inconspicuous, bugs are frequently overlooked as important factors in forest restoration projects.
You can attract invertebrates to a bush area by creating suitable habitats for them to live in. Most invertebrates need moist soil, shade, a leaf litter layer, rotten wood and food plants. In newly planted areas you can create suitable habitats by mulching around the base of plants with organic material. Once habitat is suitable, many invertebrates will return by themselves.
Whatever you do, do not underestimate the power of invertebrates!
[DOC thanks Corinne Watts from Landcare Research Manaaki Whenua for providing this text]