All I'm saying is there may be ancient features related to the spiders at lower latitudes from colder times.
In the link below around the middle of the photo the spiders stop at the edge of the depression. They have a similar appearence to what is thought to be sand dunes around objects at lower latitudes.

http://barsoom.msss.com/moc_gallery/m07_m12/images/M08/M0808054.html

Longitude of image center: 192.70°W
Latitude of image center: 77.90°S
Scaled pixel width: 5.53 meters
Scaled image width: 2.85 km
Scaled image height: 52.69 km
Solar longitude (Ls): 235.37°
Local True Solar Time: 1.47 decimal hours
Emission angle: 0.14°
Incidence angle: 80.75°
Phase angle: 80.64°
North azimuth: 256.25°
Sun azimuth: 55.25°
Spacecraft altitude: 372.57 km
Slant distance: 372.58 km