On Salisbury Plain Bill Oddie is looking for tank tracks in the mud. When it has been raining, these fill with water. Paul shows him the inhabitants of these pools - fairy shrimps. These creatures have feathery gills and were probably called fairy shrimps because they appear from nowhere when it rains. They can stay dormant in the mud for six or seven years, and they only live in temporary pools where there are no predators. They are a protected species and are very popular with naturalists who visit Salisbury Plain.