A new study reveals that endangered butterflies can find unlikely refuge in cities, if urban greenspaces are managed with connectivity in mind.

When you think of conservation, a city might seem like an unlikely helper. Across the world, urbanisation is leading to habitat loss, pushing species to extinction. Yet a new study by Leonardo Ancillotto and colleagues in the journal Urban Ecosystems shows how urban parks and gardens are providing a lifeline for threatened species like the Italian Festoon butterfly, Zerynthia cassandra.

The study of the Italian cities of Rome and Bari found that the butterfly occupied between a quarter and a third of the potential usable habitat available. Ancillotto and colleagues argue that a little more thought about connectivity in urban environments could help secure a future for species in cities.

The secret of success in the concrete jungle

Zerynthia cassandra. Photo: Lucarelli / Wikimedia Commons.

The Italian Festoon butterfly is a black and orange (or possibly yellow) butterfly, with red highlights. It grows to about 5cm or 2 inches across and is found on the Italian mainland, south of Turin and Milan, and across a fair amount of Sicily. The exact place to find them is around Aristolochia plants, in particular Aristolochia rotunda in Rome and Aristolochia clusii in Bari. The butterflies value the plants because they need a host for their caterpillars. The leaves of Aristolochia plants offer a location to lay eggs and a source of food for the hatched caterpillars.

If you’re familiar with Aristolochia then you probably find this unlikely. The leaves contain a lot of food for hungry belly. This would not be good for the plant, and so the plants protect the leaves with aristolochic acid. This chemical attacks the kidneys and, if you can eat it fior long enough, it can also cause cancer. Normally, being poisoned from birth would be bad news, but it seems to be the opposite for some caterpillars, including the Italian Festoon. Instead, the caterpillars are able to store the poisons and so become poisonous themselves to their predators. So, in addition to food and shelter, the Aristolochia plants give the insects a defence against their enemies.

The Italian Festoon’s ability to specialise on certain Aristolochia plants means that when they find them, they can exploit them – even in the middle of a city. If there are convenient plants forming green corridors between clusters then they can also disperse between these sites.

Connecting the dots for conservation

A home that others cannot exploit might seem perfect for an insect, but the specialisation has also caused the Italian Festoon some problems. The caterpillars don’t travel a lot, but you wouldn’t expect them too – they’re caterpillars. Unfortunately, the adult butterflies don’t seem to travel much either. Ancillotto and colleagues refer to earlier research showing that Italian Festoons don’t fly as well as other butterflies, and rarely travel more than 200 metres from their home plant.

This distance isn’t a hard limit, so more remote sites can be colonised, given enough time. Ancillotto and colleagues say their results show that sites even up to a kilometre away could be considered connected.

Not surprisingly, the team also found that plant abundance was a strong predictor of butterfly occurrence. Aristolochia rotunda and Aristolochia clusii like specific ecological traits. They prefer to be at ecotones, the places where habitats transition, in this case the edge of woodlands. It also likes disturbed soil patches. Here, the butterfly may be receiving some unexpected help. Ancillotto and colleagues say that the sort of patches Aristolochia likes are the sort of patches that wild boars create, and Italy is starting to experience wild boars settling in urban sites.

Something Aristolochia doesn’t like is synanthropic vegetation. These are the kinds of plants that can colonise fresh soils as opportunists, weeds being an obvious example. Instead, Italian Festoons prefer to forage among early-flowering herbaceous plants. This would tie in with the period they’re on the wing, mainly around April and May. The connections therefore aren’t just needed in the right places, but also need to be hospitable at the right time.

Butterfly-friendly management

All these requirements create difficult demands for conservation scientists. Ancillotto and colleagues write:

In our case, the ecological needs of Aristolochia plants, preferring ecotones and relatively disturbed soils, as well as the need of adult Zerynthia for early-flowering plant species in the immediate surroundings, make habitat conservation particularly challenging. The current lack of specific protection of the species’ favored habitats (despite that the European Habitats Directive indirectly protects the locations where listed species actually occur), and the obvious difficulties in mapping and quantifying ecotonal habitats and their peculiar conditions (Nowicki et al. 2013), make in fact ecotonal-specialized species highly challenging to conserve.

The possible benefit of an urban environment is that some of these demands can be met in the course of usual urban management. The authors highlight partial mowing and low intensity grazing as actions that can help create the habitats necessary for the butterflies to thrive.

They also highlight that, given the information, the public could also wish to help by planting suitable flowers to aid endangered butterfly colonisation. This has a two-fold action helping conservation. Not only are there more places to host the butterflies, there’s also less likelihood of illegal collection.

READ THE ARTICLE

Ancillotto, L., Mosconi, F. and Labadessa, R. (2024) “A matter of connection: the importance of habitat networks for endangered butterflies in anthropogenic landscapes,” Urban Ecosystems. Available at: https://doi.org/10.1007/s11252-024-01542-0.

Cover image: Canva.

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