Below are just a few of the problems caused grey squirrels.

• Grey squirrels are serious pests to forestry plantations where they
  cause damage by stripping bark from tree trunks. This may also be a
  problem in parks.
• Problems can also be caused to gardeners, allotment holders and
  market gardeners, as grey squirrels will take cereals, fruit and
  vegetables.
• In towns and cities grey squirrels are most likely to cause
  problems when they gain access to roof spaces via building defects.
  Once they have gained access squirrels can cause damage to roof
  timbers, electrical wiring and plumbing.
• Raid bird nests to prey on eggs and fledglings.
• There is evidence in England that Parapox virus, fatal to red squirrels, can be carried by grey squirrels.