The Little Things That Run The City

This is a guest post by Luis Mata. 

…let me say a word on behalf of these little things that run the world.

This quote was part of an address given by E.O. Wilson on the occasion of the 1997 opening of the invertebrate exhibit of the National Zoological Park in Washington D.C. The ultimate objective of Wilson’s address was to stress the urgent need to recognise the importance of insects and other invertebrates for humanity. He was keen to see that efforts aimed at the conservation of biodiversity were beginning to include non-vertebrate animals. In his words:

‘A hundred years ago few people thought of saving any kind of animal or plant. The circle of concern has expanded steadily since, and it is just now beginning to encompass the invertebrates.’

With The Little Things that Run the City - a close research collaboration between the City of Melbourne’s Urban Sustainability Branch, RMIT University’s Interdisciplinary Conservation Science Research Group and nine other academic and government organisations - we sought to expand this circle so that it may also encompass the conservation of insects in urban environments. We were driven by the motivation to ‘say a word on behalf of the little things that run the city’. 

The Little Things that Run the City, Mata et al. 2016.  Artwork: Kate Cranney

The Little Things that Run the City, Mata et al. 2016. Artwork: Kate Cranney

How many insect species live in your city? How are they distributed amongst the city’s green spaces and habitats? What are the ecological processes they perform and ecosystem services they deliver? What are their most frequent ecological interactions?

The Little Things that Run the City project is addressing these and other questions within the boundaries of the City of Melbourne. Here are some of our key findings:

We found that at least 560 insect species occur within the City of Melbourne’s public green spaces. These included species of ants, bees, beetles, cicadas, flies, heteropteran bugs, jumping plant lice, leafhoppers, treehoppers, planthoppers, parasitoid and stinging wasps, and sawflies. The insect group with the highest diversity was beetles, followed by parasitoid wasps and flies.

The most common species was a ‘Minute brown scavenger beetle’ in genus Cortinicara. Minute brown scavenger beetles are tiny and dark, and measure about 2 mm in length. Truly ubiquitous in the City of Melbourne, the species was collected in all studied sites and habitats, and in association with 102 different plant species – that’s 94% of all surveyed plant species!

The European honey bee Apis mellifera was the most common bee species. We also recorded many Australian native bees, including chequered cuckoo, leafcutter, and blue-banded bees.

A blue-banded bee ( Amegilla asserta ) flying towards a black-anther flax-lily.  Image: Luis Mata

A blue-banded bee (Amegilla asserta) flying towards a black-anther flax-lily. Image: Luis Mata

We have recorded at least four new species to science. These include an ant in genus Turneria, a lacebug in genus Tingis, and two jumping plant lice: Mycopsylla sp. nov. and Acanthocasuarina sp. nov..

As many as 97% of all recorded species were native to Australia. The most common non-native species was the Argentine ant Linepithema humile, an aggressive invasive species known to displace native ants and capable of disrupting ant-mediated seed dispersal interactions.

Mid-storey was the habitat type with the highest insect diversity. As many as 337 species were recorded in association with mid-storey plants. The second most diverse habitat type was tree, followed by grassland and lawn.  

The tussock-grass Poa labillardierei was the plant species with the highest associated insect diversity. As many as 103 insect species were associated with this native grass. The native wallaby grass Rytidosperma sp. and kangaroo grass Themeda triandra also had large numbers of associated insect species. The shrub with the highest associated insect diversity was the fragrant saltbush Chenopodium parabolicum, followed by sweet bursaria Bursaria spinosa, gold-dust wattle Acacia acinacea and hop goodenia Goodenia ovata.

There were over 60% more insect species in native than non-native tree species. Interestingly, however, the tree species with the highest associated insect diversity were both the native spotted gum Corymbia maculata and the non-native pepper tree Schinus molle.

We documented approximately 2,200 associations between insect and plant species. On average, each insect species was associated with 3.3 plant species. For example, the most generalist herbivore recorded in the study, a tiny green leafhopper, was recorded in association with 57 plant species, which is more than 50% of all surveyed plant species. This is assuming of course that it actually feeds on every plant species that we found it on!

A dingy swallowtail ( Papilio anactus ) in Carlton Gardens.  Image: Luis Mata

A dingy swallowtail (Papilio anactus) in Carlton Gardens. Image: Luis Mata

Half of all adult insect species recorded in the study were herbivores. Of these, as many as 68% were folivores, a guild in which species specialise to eat leaves.

We don’t know how many species were pollinators! What we do know is that as many as 25% of all recorded species are known to visit flowers to collect nectar and/or pollen – that is almost 150 species of beetles, parasitoid and stinging wasps, flies, heteropteran bugs, ants, and, of course, bees.

Over 40% of all recorded insect species were predators or parasitoids. These species are therefore capable of regulating the populations of potential insect pests.

The insects recorded in the study may supply at least two types of food: honey and lerps. We documented only one species of honey-producing bee, namely the non-native European honey bee. Lerps are crystallised protective structures made out of the sugar-rich liquid honeydew exudated by the immature stages of jumping plant lice.

The Little Things that Run the City project illustrates the importance of insect biodiversity conservation to the City of Melbourne, and by extension, to other cities worldwide. Our findings are being applied to identify where to prioritise conservation activities, guide the design and maintenance of green spaces, and assist decision-makers considering insects in broader biodiversity plans and strategies. The study is providing valuable baseline data that can be integrated into the council’s planned research agendas; for example, in future iterations of the City of Melbourne’s BioBlitz and in the future development of monitoring programs.

Our findings are also providing data to The shared urban habitat, one of the five main research lines of the National Environmental Science Programme – Clean Air and Urban Landscapes Hub, and to the recently awarded Australian Research Council Linkage Project Designing green spaces for biodiversity and human well-being.

Insects are the most diversified animal group on our planet - and in our city! From a functional perspective they are arguably the most important as well. The ‘little things that run the city’ spread seeds, eat rubbish, pollinate food crops and flowers, produce honey, keep soils healthy, help control weeds and pests, and are a food source for some of our other most dear animals, such as lizards, bats and birds. Keeping them safe and healthy within our city should be one of our top urban conservation priorities!

Dr Luis Mata is a postdoctoral researcher at RMIT University’s Interdisciplinary Conservation Science Research Group. You can discover more about Luis and his research on his research blog. 

Banner image of a shield bug from genus Cuspicona courtesy of Luis Mata.