Hotel CaliWormia – an earthworm hotel

There is plenty of exciting research on earthworms being conducted at the WUR Soil Biology group, and elsewhere in the world. For example, we have shown that earthworms can dramatically change soil chemical conditions and thereby the availability of nutrients like Phosphorus to plants, and we found that earthworms can strongly affect emissions of greenhouse gases such as nitrous oxide from the soil. Currently, we are even studying whether earthworms may increase the natural weathering rates of rocks, and thereby take up carbon dioxide from the atmosphere, helping to mitigate global warming.

But there is one problem with earthworm research: you need lots of earthworms.

Earthworms and where to find them

In our research we are interested in the functional biodiversity of earthworms: we want to study the effects that earthworms have on soil functions, taking into account variation and interactions that exists between different earthworm species. And there are plenty of earthworm species: in the Netherlands, approximately 30 earthworm species have been observed.

Finding them, however, can be a big challenge, especially in the large numbers we typically need for our experiments. Depending on the species, it may take days to weeks to find enough individuals, and for some it is practically impossible. Moreover, you can only find them during certain parts of the year: the warm summer and cold winter are generally not suitable. Buying them from commercial suppliers—where they are grown as food source for terraria or as fish bait) is an option for some species—but raises questions about their natural behavior, as they are kept in artificial substrates. Finding enough earthworms of the right species is therefore a huge practical and time constraint to our research.

What are we trying to do in the Earthworm Hotel?

We are developing a facility where we can easily collect a large number of individual earthworms from different species for our experiments, throughout the year. In a way, our hotel is set up like a Zoo, with individual areas for different earthworm species. However, there is a crucial difference: in zoos, animals are not allowed to leave their confinement and the number of species within a confinement is strictly regulated. In our setup, earthworms can leave with a little effort, and other species can enter without too much trouble. However, by making the conditions optimal for the target species we expect them to not want to.

As our facility allows the earthworms to leave, we settled for the term “Earthworm Hotel” rather than “Earthworm Zoo”. The hotel is therefore first and foremost a resource for the research we are doing: it provides the earthworms for our experiments. However, it also has another function. It is also an ideal way of showing to our fellow scientists and to the larger public that earthworms are important, that there are many species and that those species have different habitat preferences.

In other words, the Hotel also has an important outreach function. This is why we aim to make the above-ground look of the hotel as attractive as possible — even though the occupants of the Hotel rooms won’t care about that.

The setup of the Earthworm Hotel

The hotel consists of fifteen “rooms” of 3 by 3 meters each, ten of which are currently occupied. Each room is a plot of sandy soil that natural for Wageningen University Campus, delineated by wooden panels that go about 30 cm into the soil and rise 20 cm above the surface. The panels provide a hurdle for the earthworms, but don’t make it impossible for them to escape. With some effort they can climb over the top of the panels, and in principle they can burrow below them. Paved paths between the different rooms make it difficult (but not impossible) for non-target species entering from outside.

One of the most important reasons that earthworms die prematurely is drought. Many species usually die in large numbers during the summer months. To avoid this, we are providing irrigation during dry periods. In theory, serious frost also could become a problem. For that reason, we have covers that can insulate the soil during cold spells and we are thinking about slightly warming the soil during those periods to avoid freezing. But, frankly, with the very mild winters we’ve been having recently this seems hardly necessary.

All rooms are seeded with ryegrass, except the room for the compost worms that is covered with a compost heap. In the other plots, we have modified grass and fertilizer management according to the preference of the different species. For example, epigeic and anecic earthworms like to eat fresh organic matter, so we don’t remove the grass after it is mown. Endogeic earthworms don’t eat fresh organic matter but prefer more decomposed material (such as soil organic matter). Therefore, in the plots with endogeic earthworms we remove the grass clippings to not make it too attractive for epigeic and anecic earthworm species

Does it work?

Frankly? We don’t really know yet! We have been applying the right species to the right chambers for a few years now and have diversified the management of the different rooms according to what we think the respective earthworm species prefer. In the coming years, we will start to inventorize the earthworm communities in the different rooms and see how successful we have been in the first stage of the hotel. Depending on the findings, we will probably change the management of the various rooms to optimize conditions for our target species. The type of fertilizer applied might change, or we might start to grow a different crop, but it may also even mean replacing the local sandy soil with other type of soil.

Without a doubt, it will take a lot of experimentation to find the optimal conditions for the various species. So we will learn a lot about earthworms in the proces.

References

1. Blouin, M., Hodson, M.E., Delgado, E.A., Baker, G., Brussaard, L., Butt, K.R., Dai, J., Dendooven, L., Peres, G., Tondoh, J.E., Cluzeau, D., Brun, J.J., 2013. A review of earthworm impact on soil function and ecosystem services. European Journal of Soil Science 64(2), 161-18210.1111/ejss.12025.
2. Brown, G.G., Pashanasi, B., Villenave, C., Patron, J.C., Senapati, B.K., Giri, S., Barois, I., Lavelle, P., Blanchart, P., Blakemore, R.J., Spain, A.V., Boyer, J., 1999. Effects of earthworms on plant production in the tropics. In: P. Lavelle, L. Brussaard, P. Hendrix (Eds.), Earthworm management in tropical agroecosystems. CAB International, Wallingford, pp. 87-148.
3. Darwin, C., 1881. The formation of vegetable mould through the action of earthworms with observations on their habits. John Murray Publishers, London, UK.
4. Krediet, A., 2019. De Nederlandse Regenwormen. Stichting JeugdBondsUitgevery, 's Graveland, The Netherlands.
5. Lubbers, I.M., van Groenigen, K.J., Fonte, S.J., Six, J., Brussaard, L., van Groenigen, J.W., 2013. Greenhouse-gas emissions from soils increased by earthworms. Nature Climate Change 3(3), 187-19410.1038/nclimate1692.
6. van Groenigen, J.W., Lubbers, I.M., Vos, H.M.J., Brown, G.G., De Deyn, G.B., van Groenigen, K.J., 2014. Earthworms increase plant production: a meta-analysis. Scientific Reports 410.1038/srep06365.
7. Vicca, S., Goll, D.S., Hagens, M., Hartmann, J., Janssens, I.A., Neubeck, A., Penuelas, J., Poblador, S., Rijnders, J., Sardans, J., Struyf, E., Swoboda, P., van Groenigen, J.W., Vienne, A., Verbruggen, E., 2022. Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes? Global Change Biology 28(3), 711-72610.1111/gcb.15993.
8. Vos, H.M.J., Koopmans, G.F., Beezemer, L., de Goede, R.G.M., Hiemstra, T., van Groenigen, J.W., 2019. Large variations in readily-available phosphorus in casts of eight earthworm species are linked to cast properties. Soil Biology & Biochemistry 13810.1016/j.soilbio.2019.107583.