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Insects are disappearing from urban areas at a disturbingly rapid rate

The alarming rate at which insects are disappearing from our environment, especially urban areas, has become a critical concern. This catastrophic phenomenon is unfolding so swiftly it outpaces scientific study.

This urgency is underscored by the complexity of insect life cycles, including stages such as eggs, larvae, pupae, and adults, raising questions about whether all stages are declining at the same pace. Until recently, a comprehensive investigation into this matter was scarce.

Studying insect population decline in urban areas

An alarming study has shed new light on this issue, focusing on the monitoring of both adult and larval stages of moths in an urban, subtropical setting over a year.

This research marks a significant step forward, being the first to analyze multiple life stages of insects to understand the depth of their declines comprehensively.

Additionally, it’s among the few studies that probe insect population dynamics in lower latitudes, areas which are increasingly bearing the brunt of urban expansion and extreme temperatures.

Michael Belitz, the lead author of the study and a researcher at the Florida Museum of Natural History during the investigation, highlighted the criticality of subtropical and tropical environments.

Urban heat islands and insect decline

These regions not only harbor the highest insect abundance and diversity but are also experiencing the fastest rates of urbanization globally.

Belitz pointed out, “The urban heat island effect in these areas may be especially detrimental to insects,” emphasizing the adverse impact of urbanization on insect populations.

Cities, regardless of their geographical location, exacerbate the heat problem. In contrast to natural or rural settings, where a significant portion of sunlight is reflected back into space, urban materials like asphalt and concrete absorb and convert more light into heat.

This phenomenon creates “heat islands” within cities, areas with temperatures up to 7 degrees Fahrenheit warmer than their surroundings, posing a substantial threat to local wildlife, especially in warmer regions.

Illuminating the plight of moths

Robert Guralnick, co-author and curator of biodiversity informatics at the Florida Museum of Natural History, remarked on the broader implications of insect declines. “There’s no doubt that insect declines are a real phenomenon.”

He further noted the challenge in pinpointing where these declines are most acute, whether in tropical or temperate regions, emphasizing the need for detailed research across various environments.

The team’s innovative approach involved collecting moths from several locations across Alachua County, Florida, with different levels of urban development.

Capturing adult moths proved straightforward, using light sources as lures. However, locating caterpillars was more challenging due to their habitat in the tree canopy and their indifference to artificial light.

Despite these obstacles, the importance of including caterpillars in the study was clear, as Belitz noted, “Caterpillars are an important food source for breeding birds.”

Size matters: The fate of macro and micro moths

To estimate caterpillar abundance, the team utilized an inventive method involving the collection of larval excrement.

By placing funnels with attached jars beneath trees and weighing the collected pellets weekly, they could infer caterpillar population sizes.

After a year of diligent work, over 35,000 moths were collected and categorized as either macro- or micro-moths.

Macro moths, such as luna and io moths, are known for their large wings and ability to travel long distances.

Micro moths, defined in this study as those 10 millimeters or less in length, encompass a vast array of species with cloak-like wings, displaying a bewildering diversity of beiges and browns.

Both large and small moths share a similar fate

Both large and small moths face declines, but not in the ways previously thought. Larger moths, once believed to be better at navigating urban challenges due to their ability to travel greater distances, are actually at a disadvantage.

The research found that larger moths fared worse in urban areas compared to their smaller counterparts, contradicting earlier findings from a study in Belgium.

According to lead researcher Michael Belitz, the discrepancy likely stems from the difference in climate between temperate Europe and subtropical Florida, with larger moths in warmer climates expending more energy to cool down.

This observation extends to other insects, suggesting a broader pattern where urbanization favors smaller body sizes due to reduced metabolic stress.

Diet may be the key to urban insect survival

The diet of moths also plays a crucial role in their urban survival. Moths that feed on a variety of plants are more adaptable to city life than those with specialized diets, which quickly decline with urban development. This adaptability underscores the importance of dietary diversity for survival in changing environments.

Despite focusing on protected areas, the study observed significant declines in moth populations, indicating that even these spaces are not immune to the impacts of urbanization.

Robert Guralnick, a co-researcher, pointed out the misconception that city parks, which appear natural, actually host significantly altered communities compared to undisturbed wildlife areas.

“You might think that you’re looking at a natural environment when you walk into a city park, because it looks intact,” Guralnick said. “The truth is, what you see is a completely different community than those that exist in places like wildlife management areas.”

The findings are particularly alarming considering they come from Alachua County, a region in Florida less urbanized than many others, hinting at the widespread nature of biodiversity loss.

Implications and conservation efforts

The situation, however, is not beyond hope. Belitz emphasizes the potential for urban and suburban areas to support moth populations through conscious efforts to enhance their habitats.

Planting native vegetation can attract and sustain a variety of pollinators, including moths, thereby increasing biodiversity.

Additionally, reducing light pollution, which disorients and endangers moths and other nocturnal insects, presents a simple yet effective way to support these vital members of the ecosystem.

Insects, moths and humans coexisting in urban areas

In summary, this study unveils the stark reality of declining insect populations, especially moths, in urban environments, revealing how the relentless march of urbanization and the ensuing heat islands pose significant threats to insect biodiversity.

By meticulously examining both the adult and larval stages of moths, the research offers unprecedented insights into the challenges these creatures face, from the subtropical climates of Florida to the urban heat traps of cities worldwide.

Yet, amidst the alarming findings lies a beacon of hope: the potential for positive human intervention. Through simple actions such as cultivating native plants and minimizing light pollution, we can forge a path towards mitigating the impact of urbanization on moths and other vital insect species, ensuring their survival and the preservation of our planet’s intricate web of life.

The full study was published in the journal Global Change Biology.


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