The Giant Wetland Worms of South America

The Orinoco Llanos of Columbia and Venezuela were home to a mystery. These tropical wetlands are home to a landscape dominated by densely packed, regularly spaced mounds of soil. These Surales can be up to 5 m in diameter and 2 m tall and cover an area almost the size of Scotland! Rumsaïs Blatrix takes us on a journey to South America to discover how the mystery of the Surales was solved by his colleagues, Delphine Renard and Doyle McKey.

Rumsaïs Blatrix is an ecologist, mostly interested in species interactions. He works at two levels:
1. The mechanisms of interaction between individuals and their evolutionary significance (in particular deceptive pollination and ant-plant symbioses).
2. The consequences of interactions at the landscape scale (in particular the role of soil organisms in patterned landscapes).

Q&A with Rumsaïs Blatrix

How much do we know about the other species that rely on this earthworm-made habitat?
It is very well known that the termite nests in termite savannahs act as ‘fertility islands’ and support species that you wouldn’t otherwise find. It’s possible that we could have a similar situation with the surales, but we haven’t undertaken any kind of census to evidence this. It would make a very interesting study.
Are there any threats to the surales landscape of the Orinoco Llanos?
Historically this landscape was used for cattle ranching, which does not seem too destructive if it is not too intensive. The main threat facing this landscape is probably conversion to other types of agriculture, particularly for rice cultivation. This involves levelling the land and therefore destroying the mounds. Once levelled, this landscape provides the perfect conditions for cultivating rice.
Is there a specific number of worms per mound?
We don’t know, but this is one of the things we are looking into this year. Doyle McKey is undertaking fieldwork in South America to investigate this question and more. Questions he will be looking at include ‘How many earthworms are in each mound?’, ‘Is the number constant between mounds, ‘Is there any behavioural relationship between the earthworms within a mound?’ and ‘How much soil do they move?’.

Literature references

Zangerlé, A., Renard, D., Iriarte, J., Suarez Jimenez, L. E., Adame Montoya, K. L., Juilleret, J. & McKey, D. (2016) The Surales, Self-Organized Earth-Mound Landscapes Made by Earthworms in a Seasonal Tropical Wetland. PLoS One, 11(5), e0154269. DOI: 10.1371/journal.pone.0154269
Mckey, D., Renard, D. & Blatrix, R. (2021). ‘The multiple roles of soil animals in the interpretation of archaeological soils and sediments in lowland tropical South America’, in Odonne, G., & Molino, J.-F. (Eds.). (2020). Methods in Historical Ecology: Insights from Amazonia (1st ed.). Routledge. pp. 121-129. DOI: 10.4324/9780429060175
Renard, D., Birk, J. J., Zangerlé, A., Lavelle, P., Glaser, B., Blatrix, R. & McKey, D. (2013). Ancient human agricultural practices can promote activities of contemporary non-human soil ecosystem engineers: A case study in coastal savannas of French Guiana. Soil Biology and Biochemistry, 62, 46-56. DOI: 10.1016/j.soilbio.2013.02.021