Mustard Flour instead of Formalin for the Extraction of Earthworms in the Field C. H. Hogger, Swiss Federal Research Station for Agronomy, Reckenholz, 8046-Zurich, Switzerland, chhoegger@gmx.net [Here is a revised internet version for those who do not have acccess to the journal, in which the article originally appeared: Bulletin der Bodenkundlichen Gesellschaft der Schweiz (1993) 17:5-8] The standard earthworm expellants for use in the field are formaldehyde solutions with concentrations of 0.1 to 0.5% (Daniel, 1986; Lee, 1985). This compound causes concern for health and environmental reasons. Gunn (1992) described the use of English mustard paste as an earthworm expellant for the first time in studies on park grassland. Mustard extracted more earthworms than formalin. The following is a comparison of a mustard flour method with a formalin standard on permanent agricultural grassland and in a maize field in 1992. Materials: Metal rings covering 1/4 m2 (56 cm diameter, 15 cm high; stainless steel is most stable, or any other ring, which may be pressed into the soil). Strong board, about 60x60 cm for pressing the ring into the soil. Several canisters for water, about 20 liters Measuring beaker or pail, 5 liters Measuring cylinders, 0.5 and 0.05 liters Collecting vessels with lid, about 0.5 liters Plastic flasks with wide screw cap, 1 liter Plastic flasks with wide screw cap, 100ml Plastic forceps with smoothed ends to avoid wounding of the worms Mustard flour (from a restaurant supply house) Formalin (= 38 to 40% formaldehyde) Disposable plastic gloves Lawn shears, if possible electric, or sickle Procedure: 1. Weigh out 100g mustard flour and put in small plastic flasks in the lab; Add 100g mustard flour to 1 liter flasks and fill up to 1 liter with tap water; shake well (=10% mustard flour); to be used on the same day. 2. Put the metal rings into the field; cut the grass and remove it; press the rings about 2 to 3 cm into the ground by jumping on the board. 3a. Shake the mustard suspension again and pour 165 ml into the measuring beaker or pail; fill up to 5 liters with tap water (= 0.33% mustard powder). or 3b. For the formalin standard method 12.5 ml formalin in 5 liters of water are used (=0.1% formaldehyde). 4. Pour the respective suspension / solution into the ring 5. Collect the earthworms with forceps and put them into the collecting vessels, which contain about 3cm water. 6. After 15 to 20 minutes pour again 5 liters of the suspension into the ring, and optionally after 15 to 20 minutes repeat again. The extraction time is therefore at least 30 to 40 minutes, or until no more worms appear. 7. In the laboratory count, weigh and identify the worms. The biomass can be estimated also by measuring the water displacement of the worms in a measuring cylinder. Results: The results in Fig. 1 were obtained with 1%, 0.33% and 0.1% mustard flour and 0.25% formalin in permanent grassland with three replications for each mustard concentration and formalin. The extraction efficiencies of 0.33% mustard flour and 0.25% formalin was not significantly different (Fig. 2). With 1% and 0.1% mustard significantly fewer earthworms were expelled. With 0.1% mustard the earthworms took longer to appear on the soil surface and the extraction was less complete than in the other treatments. The weight in this treatment was significantly lower than with 0.25% formalin. In a maize field there were no significant differences between 0.25% formalin and 0.33% mustard flour for numbers and weights of the earthworms (p> 0.08, n = 12; Fig. 3). Mustard flour is a harmless extraction agent without health hazards and the vegetation is not damaged either. Mustard flour was also easier to weigh than the mustard paste as used by Gunn (1992). In initial trials different mustard pastes gave different extraction efficiencies. For school and demonstration purposes mustard flour is the ideal earthworm expellant and apparently also for research purposes. The active ingredients are probably volatile or non-volatile mustard oils, which we enjoy as spice in our food. Thanks are due to M. Waldburger for the simultaneous extraction of the earthworms with formalin in the maize field. Literature: Daniel, O. 1986. Diurnale Effizienzschwankungen beim Sammeln der Regenwurmart Lumbricus terrestris mit der Formaldehydmethode. Bull. Bodenkundl. Ges. Schweiz 10: 39-44. Gunn, A. 1992. The use of mustard to estimate earthworm populations. Pedobiologia 36: 65-67. Lee, K.E. 1985. Earthworms. Their Ecology and Relationships with Soils and Land Use. Academic Press. London. 411p. Original Text revised 27 January 2001
