Dr. Shepherd and Dr. Brantley have developed a sampling regime that requires destructive sampling. Using this method, the field team takes crust samples of approximately 8cm3 each (i.e., 2cm x 2cm x 2cm). We have chosen the small sample size for conservation reasons. In early studies we attempted several sampling techniques, but found it was necessary to harvest the crust. Crust samples will be preserved in 70-80% ethanol and samples can be maintained at this stage for long periods if necessary.
On return to the lab, we harvest the animals using a modified version of the heptane flotation method described by Walter et al. (1987) and Kethley (1991). We decant the ethanol into beakers and break up the crust sample in deionized water. To the crust sample we add a small amount of heptane (to which arthropod exoskeletons readily adhere). The two layers (water and heptane) are thoroughly mixed using a magnetic stir plate to ensure that the heptane comes into contact with all the water. The heptane layer is then drawn off and transferred to the beaker containing the original ethanol from the sample. We then evaporate the heptane layer, leaving behind the ethanol containing arthropod specimens. Finally, this alcohol sample is scanned under the dissecting scope at high magnification (90X). Arthropods are removed from the sample and transferred to small vials of 70-80% ethanol for later slide preparation. Specimens are cleared in lactophenol if necessary and mounted on slides in Hoyer's medium. Those too large for permanent mounts are maintained in vials of alcohol. These specimens can be temporarily mounted in concavity slides for identification.
We have chosen this extraction method over the more commonly used funnel-harvesting techniques for several reasons. 1.) Arthropods can be preserved in the field, allowing the field team to travel to multiple sites before returning to the lab. 2.) Unlike funnel methods that depend on animals being alive (MacFadyen 1962, Edwards and Fletcher 1971), flotation methods recover microarthropods from soil and litter samples whether they are dead or alive by capturing them in a solvent or supersaturated salt solution that the sample has passed through. 3.) Results of comparative studies show the flotation method is ideally suited to harvesting suites of desert-adapted arthropods that, due to their life history traits may not respond to moisture gradients set up by funnel techniques (Walter et al. 1987). Walter et al. (1987) have demonstrated recovery rates of 78% of known soil microarthropods from a single flotation cycle. Finally, Dr. W. Welbourn, who works on prostigmatids, strongly approves the heptane flotation method for work with prostigmatid mites (pers. comm.).