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A relaxed attitude, dense plantings and more native plants are key in providing for invertebrates in gardens.

The second set of results from the Wildlife Gardening Forum-inspired Plants for Bugs project, run by the Royal Horticultural Society have, at last, been published. They indicate that the more garden greenery and more native plants in gardens the more plant-dwelling invertebrates will be supported. 

Writing the paper and the peer-review process took a while, but after a rejection, re-analysis and two rewrites (not unusual for scientific works) the paper was accepted and published.   Perhaps more importantly it has been interpreted for the home gardener and recommendations have been prepared for gardeners wanting to provide for invertebrate life.

The paper, “Enhancing gardens as habitats for plant-associated invertebrates: should we plant native or exotic species?” has been published in Biodiversity and Conservation, a title intentionally similar to the first paper’s from the project - “Enhancing gardens as habitats for pollinators: should we plant native or exotic species?”. The first paper reported on insects that visited  flowers – ‘pollinators’. This popular group covers honey bees, bumblebees, hoverflies etc., which proved to be supported best by gardens planted with plenty of flowering plants from different regions; for more detailed recommendations see the RHS's bulletin.

The second paper deals with a dataset of about 23,000 individual specimens  that were sampled from the greenery (leaves and stems) over four years, hence termed ‘plant-inhabiting invertebrates’ (catchier terms eluded us – suggestions welcome!). These invertebrates were categorised into four  functional groups determined largely by what they feed on:  herbivores (plant-eaters), predators (animal-eaters), omnivores (plant and animal-eaters) and detritivores (organic matter-eaters or recyclers). Everything from caterpillars and aphids, to thrips, ladybirds, true bugs, spiders, earwigs and springtails.

But wait, aside from predators such as ladybirds, why on earth would the average gardener be keen to help invertebrates that may eat plants, often regarded as pests?   A valid point, but you need a balance and a healthy food chain – predators need prey i.e.  no aphids means no ladybirds. So some ‘pests’ are vital to support healthy populations of predatory invertebrates which can assist in pest control. They also provide food for garden birds and mammals such as hedgehogs. In short, an abundance of bugs of all types equates to healthy garden ecology.

To summarise the research the recommendations for providing for invertebrates living on the greenery in the garden are:

1. Plant a predominance of plants native to the UK (if you live in the UK of course!).

2. Even if you don’t have a lot of native plants in your garden, planting schemes that are based on plants native to the Northern hemisphere are likely to support only marginally fewer (less than 10%) invertebrates than exclusively UK native plant schemes. And exotic plant schemes based on Southern hemisphere plants will still support a good number of invertebrates too, albeit around 20% fewer than plants from the UK.

3. Regardless of plant origin, the more densely your garden is planted or allowed to grow, the greater the abundance of invertebrates of all kinds (herbivores, predators, detritivores and omnivores) it will support.

To put it more simply and practically, gardeners who want to maximise invertebrate abundance can:

•  Include plenty of UK native plants
•  Decide priorities – more plants from the Southern hemisphere help certain pollinators (findings from paper one)
•  Let your plants fill out
•  Plant generously
•  Be relaxed and tolerate some nibbled leaves

…and we haven’t finished yet, pollinators and abundance of invertebrates are only part of the data collected from the four year experiment. There is data on species diversity, pitfall traps yet to be investigated. Then it all needs putting together into coherent advice, and so it’s onto writing the next paper......

Planting for invertebrates, what really is best in gardens? New research gives some indications.

Andrew Salisbury – Forum Trustee