The first global atlas of earthworms has been compiled, based on surveys at 7,000 sites in 56 countries.
The findings will help protect the hundreds of different earthworm species found on all continents except Antarctica.
Climate change might have "substantial effects" on earthworms, said an international team of scientists.
The burrowing creatures play a vital role in improving the soil but little is known about them on a global scale.
We rely on earthworms for increasing crop yields and aerating the soil, but they have been overlooked in the past, said Dr Helen Phillips of the German Centre for Integrative Biodiversity Research in Leipzig.
"As children probably the vast majority of us held earthworms in our hands and probably weren't quite aware how significant they are in the environment and for the things that we rely upon," she said.
"We should never stop looking at the above ground biodiversity but we really shouldn't be overlooking what's beneath our feet, as well."
The international team of 141 researchers from 35 countries mapped global patterns in the number and type of different earthworms and how this is related to factors like soil pH and the climate.
They discovered that temperature and rainfall can shape patterns of earthworms in the soil, suggesting climate change might have "serious implications" for both earthworms and the services they provide to nature.
Dr Noah Fierer of the University of Colorado, Boulder, who is not connected with the study, said the results underscore that earthworm distributions are highly sensitive to climate, though "it remains unclear how earthworm communities will respond to ongoing climate change".
The study, published in Science, found that at a local level, the number of species and the abundance of earthworms is lower in the tropics than in the temperate regions.
For example, the soils of southern England are an earthworm paradise, harbouring some of the highest diversity and abundances of earthworms in the world.
Facts about earthworms
- Earthworms are surprisingly abundant in soil; a single square metre can contain more than 150 individual earthworms
- They are also very diverse; with at least 6,000 known species varying in size, colour and appearance from the just a few cm to 3m in length
- In the UK alone, there are about 30 earthworm species.
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