Byers, J.A., & Poinar, G.O., Jr. 1982. Location of insect
    hosts by the nematode, Neoaplectana carpocapsae, in
    response to temperature. Behaviour 79:1-10.
nematodes in agar above wax moth larva taped under petri dish The bottom two lines scratched in agar traced the outlines of a wax moth larva (about 2 cm long) that was taped on the underside of the plastic petri dish. Several hundred nematodes were released on the agar surface and after several hours of dispersal the petri dish was photographed. It is possible to see that more nematodes were swimming over the wax moth (due to metabolic heat conducting through the plastic and agar) than were swimming in slightly cooler areas. In fact, the agar above the wax moth (that was taped under the plastic petri dish) was found to be only 0.3 above ambient with an electronic thermometer.

nematode paths shown in India ink on agar In this photo hundreds of nematodes were released in the center of the petri dish (bottom center). The dish was filled half way with agar and then a thin film of India ink (carbon particles) was poured over the agar. The nematodes "plow" the carbon particles causing their paths to show up under illumination. The paths appear to be rather random with a forward component, much as the paths of any moving animal is in the absence of any landmarks.
Chemical Ecology
Swedish University of Agricultural Sciences
S-230 53 Alnarp