Urbanization causes massive decline in insect pollinators

Urbanization may seem harmless at first glance. Yet beneath the pavement and concrete lies a growing crisis. A new study from the University of Sheffield reports that urban areas support 43 percent fewer pollinating insect species. These losses have consequences for both ecosystems and crop yields.

Researchers sampled allotment sites across Sheffield, Leeds, and Leicester. These plots varied in proximity to city centers. The closer they were to concrete-heavy areas, the fewer pollinators they supported. Insect abundance and richness fell sharply in built-up zones.

Bees often dominate the conversation. But this study highlights that moths and hoverflies also matter. These two groups of pollinating insects showed higher sensitivity to urbanization than bees.

Why some insect pollinators struggle

Bees tend to persist in urban areas due to their simpler needs. They depend mainly on flowers for both adult and larval food. Urban greenspaces often provide these resources in abundance.

Social bees, like honeybees and bumblebees, show strong adaptability because of their generalist foraging behaviour and long flight ranges.

Moths and hoverflies, in contrast, need diverse resources. Many hoverflies breed in stagnant water or rely on prey for their larvae. Moths require tree cover for daytime roosting and specific plants for their caterpillars. These features are often lacking in urban environments.

Trees help insect pollinators survive

The study confirmed that habitat type shapes pollinator survival. Semi-natural habitats supported all three major insect groups, but tree canopy cover had a uniquely strong effect on moths. Moth species richness and abundance rose significantly with increasing tree cover.

Gardens, however, had no consistent effect. Although common in cities, their quality varies widely. Many gardens include lawns, paving, or ornamental plants not suitable for pollinators.

Urban layout influences insect declines

Urban landscapes form a mosaic of impervious surfaces, fragmented greenspaces, and isolated habitats. These patterns influence how different pollinators respond.

Hoverflies and moths saw the steepest declines in areas with high impervious surface cover.

For every 10 percent increase in concrete or tarmac, species richness dropped by up to 7.5 percent.

These declines occurred across different scales – within 250, 500, and 1,000 meters of the sampling sites. The loss of moth and hoverfly abundance was especially strong at closer ranges.

Pollinators do more than pollinate

Pollination is just one part of the ecological role these insects play. Hoverfly larvae, for instance, prey on crop pests like aphids.

Moths help recycle nutrients through their feeding and contribute to food chains. Birds and bats feed on them, linking lower and higher levels of the ecosystem.

The loss of moths and hoverflies doesn’t only threaten pollination. It weakens entire ecosystems. Without them, pest control declines. Nutrient cycling slows. Predators struggle to find food.

Redesigning cities for insects

To reverse this trend, cities must do more than plant flowers. They must support a variety of habitats. Increasing tree cover, preserving semi-natural green areas, and reducing fragmentation can help.

The study urges planners and policymakers to consider the varied needs of pollinator groups.

“All pollinating insects struggle to find suitable food and habitat in cities,” said study co-author Stuart Campbell. “The greater sensitivity of hoverflies and moths to urbanization might be due to their ecological requirements.

“All of these species need flowers to feed on, but moths also require tree and shrub canopies, and food plants for their caterpillars, while many hoverflies require stagnant water to breed.”

“These are all habitat characteristics that can be much harder to find in more heavily built up areas, and we will need to consider these features in order to conserve such a diverse group of insects for future generations.”

Moths and hoverflies need attention

Study lead author Emilie Ellis noted that the scale of the threat to many pollinator species remains relatively unknown due to a global focus on bees.

“However moths and hoverflies are just as important for our ecosystems, and our results show they may be particularly vulnerable in urban habitats,” said Ellis.

Understanding insect needs can help protect them. Cities must consider more than floral density. Structural vegetation like trees and complex ground cover matter too. So do aquatic features and undisturbed soils.

Urbanization affects insect pollinators in complex ways. While bees survive on city flowers, moths and hoverflies face harsher challenges.

This study highlights the urgent need for diverse, well-structured greenspaces. Pollinators don’t all need the same things. But all need us to pay attention.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–