Moth walls: shedding light on moth biodiversity

Lepidoptera is a hyper-diverse order of insects composed of moths and butterflies. There are at least 160 000 species of Lepidoptera globally and moths represent approximately 90% of these species, the majority of which are nocturnal (Pohl et al. 2019). Moths contribute to important ecosystem services such as pollination (e.g., Alison et al. 2022) and herbivory (e.g., Dhileepan et al. 2018), and serve as a key food source for vertebrates such as birds and bats (e.g., Visser et al. 2006; Kolkert et al. 2020). For example, nocturnal moths can be more species diverse than day-active pollinators in agroecosystems and many serve as key pollinators for diverse wild plants (Walton et al. 2020). Others that act primarily as agricultural pests have been found to constitute about 75% of the diet of local bats (Kolkert et al. 2020).

Most countries lack sufficient data on the distribution and abundance of moth species. In countries where long-term monitoring data do exist, however, moth biodiversity appears to be on the decline (e.g., van Langevelde et al. 2017; Fox et al. 2021). This information would not be available without grassroots monitoring efforts. For example, the British Butterfly Monitoring Scheme began as a rather humble monitoring project in the mid-1970s in response to concerns about declines in butterfly abundances (Pollard and Yates 1993). This program now boasts the most comprehensive long-term data on butterflies and moths in the world (Fox et al. 2021), in large part due to contribution from volunteers. Community science (often called citizen science) platforms (e.g., eButterfly, eBird, iNaturalist, etc.) are unparalleled in their ability to broaden monitoring efforts critical to our understanding of the conservation status of target species.

For more than a century, artificial light sources have been used to attract night-active insects (e.g., Wallace 1869). Over this time, gas lamps have been superseded by incandescent bulbs, mercury vapour bulbs, blacklight fluorescents, and, more recently, light emitting diodes or LEDs (Niermann and Brehm 2022). So-called “light trapping” has proven to be a particularly effective means to collect nocturnal insects belonging to several orders including Coleoptera (beetles), Hemiptera (true bugs), Hymenoptera (e.g., wasps), Trichoptera (caddisflies), Diptera (flies), and most notably Lepidoptera (i.e., moths). Their flight-to-light behavior poses an attractive opportunity for systematic monitoring of moths at broad spatial and temporal scales. For decades now, small groups of naturalists and scientists have used blacklights and other artificial light sources opportunistically to attract and document nocturnal insects, yet there remains great untapped potential for engagement with the broader public on the diversity, beauty, and wonder of these species and their importance to many natural processes. Done well, such efforts can greatly contribute to our collective understanding of moth diversity and distribution.

The moth wall idea was first implemented in 2013 at a research station of the Natural History Museum Aarhus in the Danish national park Mols Bjerge to engage the public about this important and diverse group of insects. This in turn has led to the documentation of 11 310 moth records comprising 663 species that have been documented from that one site alone, an accomplishment brought about by significant direct engagement of the public. At least 12 more moth walls have since been installed in eastern Canada and the United States by communities, NGOs, and government organizations.

Each moth wall (Fig. 1) is composed of a wooden board (i.e., partial sheet of plywood) painted with light grey or white paint mixed with sand, which provides texture for attracted insects to grip, and a light fixture. The wall itself can be quite small ∼1/16 sheet of plywood, but the size may influence the number of individuals and therefore diversity that land on the wall. The light source is much more important. Early versions employed relatively broad-spectrum mercury vapour bulbs while current versions leverage the more targeted emissions of blacklight fluorescents or LEDs, which primarily produce the UV wavelengths (350–450 nm) most attractive to moths. Recently developed LepiLEDs (Brehm 2017) expressly designed to attract moths can run for multiple nights using USB lithium battery packs, opening opportunities for the deployment of moth walls to areas without grided electricity. This could be particularly useful in rural and remote areas.

In Canada, moth walls have been established in six provinces (the four Atlantic Canadian provinces, Québec, and Ontario) at National and Provincial Parks and some communities with trials beginning 2018. These walls have already been the focus of public engagement with several “bioblitz-style” events hosted during National Moth Week (Fig. 1, https://nationalmothweek.org/). They have also yielded four new moth and one true bug (Hemiptera) species records for Prince Edward Island and one new record for Newfoundland and Labrador. The walls used in Atlantic Canada were constructed for a cost of approximately $150 CAD each, not including the cost of electricity to power the lights. Lights can be turned on physically or with timers from dusk and until the end of a public engagement/observation event or left on until the middle of the night (∼2–3 AM). The moth walls can be visited during the early morning hours while some moths remain on the wall from the night prior. Alternatively, during the evening while moths are actively attracted to the light can be a very engaging time. Moths can then be observed and photographed and those images uploaded to iNaturalist to deposit the image as data. Field guides (e.g., Petersen Field Guide to Moths of Northeastern North America) may also be referenced. Locally, once species lists are established, placards or information pamphlets could be produced by communities or organizations and made available as reference material. Moth walls can be in operation from spring through to the fall months in temperate zones or year-round in warmer climates. Peak flight times (opportunities to observe the highest diversity of species) typically occur mid-late July in temperate zones that roughly coincide with National Moth Week.

Opportunistic community science-based monitoring schemes have led to successful detection and documentation of diverse species (e.g., eBird, eButterfly, iNaturalist), revealing spatial and temporal patterns in their occurrence and abundance (e.g., Prudic et al. 2017). These types of community collected data can have significant regional or national policy implications. Furthermore, community science infrastructure like moth walls can contribute to reducing gaps in equity, diversity, and inclusion by increasing accessibility to science and empowering communities or organizations to collect scientific data. They can facilitate capacity building and collaboration between science-based organizations and communities. The information boards guide people on how they can contribute data, and they share science-based information. Also, public events can foster inclusion by improving opportunities for marginalized groups to participate. This may include people from underserved communities in urban or rural settings, different backgrounds, or low-income households who can participate in and benefit from these scientific endeavors.

Each individual moth wall can gather local moth biodiversity data and grow knowledge and educational opportunities at relatively little cost. Working together as a network, moth walls can reveal larger patterns in the diversity and distribution of this taxon while enabling stakeholders to engage the public about its ecological and economic importance.

Moth walls provide great opportunities for stakeholders to directly engage and educate the public about light-attracted insects. These could include interpretation events to discover their biodiversity and highlight their important roles in local ecosystems. Targeted calls for help in documenting species of economic or conservation concern, potentially in collaboration with local organizations, offer other valuable opportunities to educate citizens about environmental concerns in their area. Many species completely lack baseline population and distributional data; this collaborative monitoring approach can assist in providing those data for initial assessment while also tracking changes in response to human and natural disturbances.

Moth walls present an opportunity to engage youth to discover the seemingly endless diversity of colour, shapes, and forms of insects and how those relate to their numerous roles in nature while exposing them to science via a fun outdoor activity. This involvement not only enriches scientific endeavors in youth but also nurtures a sense of environmental stewardship among them. Members of remote and rural communities with greater reliance on ecosystem services could gain useful practical knowledge from these activities, while those of suburban and urban communities can strengthen their connection with and appreciation for nature otherwise rarely seen in the city. In both places, moth walls can also serve as key monitoring tools for the detection of irruptive or non-native species introductions of ecological or economic importance. Similarly, moth walls could be used by schools to engage children about the importance of insects and biodiversity. They could be interacted with towards the beginning (September and October) or towards the end (May and June) of the school year where students are challenged to document the most species records, for example.

In campgrounds and parks, this infrastructure presents real-time opportunities to engage visitors on the importance of this insect group (and others) via interpretation opportunities, but also an opportunity to enhance park-visitor experiences. Moth wall visitors may better understand the value of monitoring insect groups and could be motivated to continue to participate in community science activities well after their visit.

Online open-source data platforms accumulate disparate community science observations producing large-scale datasets for use in decision-making by researchers, communities, NGOs, policy makers, land managers, and other stakeholders. Moth wall visitors are encouraged to submit their observations to a dedicated iNaturalist project (Fig. 2), where they are stored and made available to use by anyone for any purpose. For example, an iNaturalist observation was recently used to re-discover a rare moth species (Heterosphecia tawonoides) not seen since its description in 1887 (Molyneaux 2023). The added benefit for the public (or otherwise non-entomologists) is that machine learning identification algorithms, built into these applications, provide instant suggestions of possible species and then records can become “research grade” (and often vetted by experts), where data can be used for research purposes.

From a scientific perspective, iNaturalist observations can also help fill data gaps in time and space when modelling trends in insect populations (e.g., Davis et al. 2023). Over time, such data may help researchers elucidate patterns in the flight phenology of local moth species as well as the presence of species records in various jurisdictions (e.g., parks, provinces, states, etc.). Northward expansion due to climate change or delays in nightly activity due to light pollution can also be detected. Range expansions of insects have already been documented via community science contributions (e.g., Cheng et al. 2019). In northern regions, where climate change is particularly pronounced, rural and remote areas are particularly data deficient so moth walls can enable local communities from those areas to gather a baseline of data and track biodiversity changes over time. The choice of location for moth wall(s) depends on stakeholder objectives. For example, if one aimed to maximise the number of species detected, they may seek to establish them along intersecting “flight” corridors or habitat transitions, such as along field-forest edges. Similarly, specific microhabitats could be targeted if the aim was centred on conservation efforts or monitoring for particular or invasive species; alternatively, simply public engagement (areas with high visitor frequency) may be the focus of placement. Generally, brightly lit areas should be avoided to minimize the number of moths drawn away by other light sources. Similarly, if replicate walls are used for monitoring/surveillance, they should be placed at least 50 m apart so as not to draw moths from the same source pools. Ultimately, the best placement is where they will be used most (e.g., by public, park attendants, etc.).

Moth walls can be of great benefit to stakeholders interested in public engagement about nature or insect diversity and distribution, including rare and non-native species relevant to ecosystem health. This simple structure is also a means for communities to interact with nature and accrue knowledge on insect diversity around them. Inspiring the younger generation to get involved in the world of insects, moth walls can greatly benefit the broader entomological community by increasing monitoring capacity in a time of unprecedented global insect declines (Wagner et al. 2021, and references therein). While soon the integration of automated monitoring systems might accelerate our capacity to process insect imagery data at scale, the human element of community science will remain fundamental to the identity of the moth wall project as its success depends on the transformative power of personal encounters with the natural world.

We would like to thank those communities (Conne River, NL), municipalities (City of Toronto), and provincial agencies (Ontario Parks) with whom we have had very fruitful discussions about moth walls and who have expressed interest in this project and the use of this infrastructure to document species diversity and connect society to nature. We would also like to thank folks at Parks Canada, especially Cedric Davignon and Melanie Richard, for their interest in this project and interest in engaging the public about community science and moths. This interest provides us the motivation to keep growing this network. We would also like to thank Brigitte Richard with NRCan who has contributed greatly to communications efforts.