Planthopper Nymph

A nymph of Issus coleoptratus (Hemiptera: Issidae).  The white 'tail' consists  of strands of wax that are secreted from special glands.  Why these particular nymphs produce these strands is unclear but many adult planthoppers produce white fuzzy tangles of wax strands to protect themselves or their eggs from attack by predators or parasites, or from damage by rain or sunlight (see here).

Photo taken in Whiteknights Park, Reading, UK, on 2012-05-21.