Pesticides have a direct impact on the physiology and behaviour of earthworms, a trans-European research team has found.

After having studied earthworms exposed to pesticides over generations, the team, made up of researchers from institutes in France and Denmark, found that worms in fields treated with chemicals only grow to half their normal weight and do not reproduce as well as worms in fields that are not sprayed.  

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Earthworms mainly feed on organic matter such as decaying plant and fungal matter and bacteria. The material is broken down and transported into the soil, and the creatures' burrowing activity brings air in to the soil.

The Danish team, made up of Nicolas Givaudan and Claudia Wiegand, said, "We see that the worms have developed methods to detoxify themselves, so that they can live in soil sprayed with fungicide. They spend a lot of energy on detoxifying, and that comes with a cost: The worms do not reach the same size as other worms, and we see that there are fewer of them in sprayed soil. An explanation could be that they are less successful at reproducing, because they spend their energy on ridding themselves of the pesticide."

Prof Wiegand led the research together with Francoise Binet from the University of Rennes 1 in France. The scientists set out to study the behaviour of the earthworm species Aporectodea caliginosa. 

They compared soil from an organic field with that from a conventionally farmed one that had been sprayed with fungicide for 20 years, both from farms within the same area. The conventional soil had remnants of fungicide Opus® at a level common in fields. The researchers said that, when crops are sprayed with fungicide, only a small part of the chemical is absorbed by the plant. The waste can be up to 70 per cent, and much of the fungicide ends up in the soil, hence their desire to study the effects on soil-dwelling creatures.

Speaking about the 'detoxification' method observed in the worms from the conventional field, Wiegand and Biney said worms' metabolic rate increased, but a certain process involving proteins and amino acids was observed only in worms from the field where chemicals had been sprayed previously, which they claimed suggested a detoxification mechanism. "They [the worms] also increased their feeding activity, possibly to compensate for the increase in energy demand", the researchers added.

Studies have found that unsprayed soil can contain two to three times more earthworms than sprayed soil. The team suggested, "The reason for this may be that earthworms in sprayed soil do not reproduce as successfully as worms in unsprayed soil, because they need to spend more energy on detoxifying."

They also weighed the worms in the experiment and found that the worms exposed to fungicide weighed only half as much as the worms in organic soil. Worms in organic soil had an average weight of 0.6 grams, worms in conventionally cultivated soil had an average weight of 0.3 grams.