The above figure is a discrete biased random walk simulation of nematode movement in response to a chemical attractant. The black dot represents the nematode starting position, and the colour banding represents the concentration of the chemical attractant. With the highest concentration being closest to the chemical source on the left hand side. Note, the looping type behaviour that the nematode trail (in white) exhibits and then a change to a more linear trail (roughly half way) as well as the linear chemical gradient. The nematode enter the attractant source (the left hand boundary) at a time t=24. More detail on this work and these simulations can be found in Anderson et al., 1997b

The above figure is a discrete biased random walk simulation of nematode movement in response to a chemical attractant within a heterogeneous environment. This simulation is actually being performed on a digitised soil section that real nematodes moved through, the structure can easily be seen by the regions of zero attractant concentration. It is clear that the heterogeneity of the structure has altered the linear attractant gradient, observed above, to produce a nonlinear gradient. The structure has also had a significant affect upon the nematode trail, causing the simple looping behaviour to become more compact and random. The nematode still manages to get to close to the attractant source (on the left) but never manages to get all the way across. Taking over 7 times longer than the nematode in the homogeneous simulation to reach this position, the slowing effect of the structure is clear. These differences were also observed experimentally, see Anderson et al., 1997a