Insect Calculator Reveals How Mowing Affects Meadow Wildlife

Beneath flowers and grass stems, thousands of insects and spiders live, feed, breed and contribute to healthy ecosystems.

Many species pollinate plants, while others decompose organic material or become prey for birds and small mammals. Yet most people do not witness what takes place when a meadow is cut.

A new online tool makes this hidden world more accessible by presenting scientific research in a form that anyone can follow.

Rather than depending on assumptions, the tool calculates the likely number of insects and spiders in a meadow and illustrates how alternative mowing approaches may affect them.

Its purpose is to support more informed green-space management decisions and give the public a better understanding of wildlife that is usually overlooked.

From research to practical use

The web-based Insect Calculator estimates both the abundance and diversity of insects and spiders in grassland habitats.

It also enables users to compare mowing methods and see straight away how their decisions could alter local biodiversity.

Researchers developed a formula based on twelve separate variables to estimate the number of insects present in each square metre of meadow.

This formula is based on standardised field data gathered across several parts of Germany and Switzerland; the same dataset underpins the online calculator.

The calculator was created as part of the BioDivKultur project, an interdisciplinary initiative involving TU Darmstadt researchers and field-based partners.

What the figures show

The results demonstrate the substantial effect that mowing has on meadow life. According to the researchers, a single cut can lower insect and spider numbers by up to 73 percent.

A similar trend was found among numerous groups, including cicadas, bugs and grasshoppers, although the scale of the impact differs between them.

The team also found that grasslands in less isolated rural settings tend to contain denser insect and spider populations than green spaces enclosed by heavily built-up urban surroundings.

The choice of mowing machinery also has an effect. Mulchers were associated with larger reductions in insect populations than bar mowers.

Mowing frequency, cutting height and various other management decisions were likewise shown to affect the number of insects living in a meadow.

Uncut grass has an impact

One management approach emerged as particularly important in the research: leaving areas of meadow uncut.

“One key finding is that whilst changes to mowing practices can have an effect – such as using mowers that are less harmful for insects or reducing the frequency of mowing – mowing itself has the greatest impact,” said study lead author Johanna Berger from the Technical University of Darmstadt.

“This highlights the importance of areas left unmown – so-called refuges. They are an effective measure for protecting insects and spiders, as they preserve resources and provide places for them to take refuge during or after mowing,”

Creating insect refuges through rotational mowing

Rotational mowing offers one method of establishing these refuges. Rather than cutting a whole meadow in one go, managers mow one section and leave another standing until a later date.

This allows insects and spiders to persist in part of the habitat while the cut area recovers.

The calculator provides an example for a meadow of roughly 100 square metres. When the entire site is mown, approximately 13,000 insects and spiders remain.

Keeping 10 percent of the meadow uncut raises this total to 14,350. Leaving 20 percent untouched increases it to 15,700, and retaining 30 percent brings the figure to 17,050.

A meadow left completely unmown supports around 26,500 insects and spiders.

An Insect Calculator for all users

The Insect Calculator features a Walking Mode for the public alongside an Expert Mode for those responsible for grassland management.

“For the Insect Calculator, we have compiled a comprehensive dataset from standardized one-square-meter samples of insects and spiders from Germany and Switzerland,” said Nico Blüthgen, project spokesperson for BioDivKultur.

“On this basis, it is possible to clearly demonstrate how various mowing parameters and the sealed area surrounding green spaces affect the number and diversity of insects and spiders.”

Tackling the biodiversity crisis

Study co-author Margarita Hartlieb said the tool also supplies further material, including links to records from the iNaturalist citizen science project.

“Our understanding of the biodiversity crisis is growing, but there is still a lack of effective measures and action,” Berger said.

“A key solution for us in the scientific community is to link our findings to practical applications and communicate them more effectively, for example through digital and data-driven tools such as our Insect Calculator.”

The complete study appeared in the journal Ecological Solutions and Evidence.