Invasive alien species in the Urban Environment

Invasive alien species in the Urban Environment

Research and species distribution data shows that where there are more people there are more invasive alien species. Hotspots for numbers of invasive species tend to be where people frequent the most and its logical that this is the case.¬† It is because of peoples actions that alien species are in places they wouldn’t have made it to on their own accord.

Intentional and unintentional introductions

Alien species are introduced into new areas intentionally or unintentionally. We have a long history of intentionally introducing plants for our gardens, for providing game cover or as an oxygenating plants in ponds but these can spread by seed or rhizome and become invasive in favourable habitats. Some folk intentionally release animals into the wild for sport or other misguided reasons and pets can and do escape. Many alien animals won’t survive our environment but some will thrive and become invasive. It is illegal to release alien animals to the wild in Ireland and if you keep one of the Invasive Alien Species of Union concern regulated across Europe, then the species must be kept in confinement so not allowed to escape, not be permitted to reproduce and can’t be traded or transported in Ireland without a permit.

Accidental introductions also occur and most often this tends to be for smaller species or reproducing parts of plants. Perhaps the bird seed in the feeder has alien species seed in it that can spread and grow; imported vegetables have Harlequin ladybirds on them; vehicles or machines can move seed or plant fragments on wheels, tracks etc from one site to another or as happened lately, on returning home holidays abroad a person opened their suitcase and out flew a potentially invasive insect.

Some actions we can do to prevent introduction and spread in urban environments:

  • Use native species bird seed and wildflower mix
  • Prevent pets from escaping – Be Pet Wise
  • Never release an unwanted pet into the wild. Re-home if possible or have euthanized.
  • Remove invasive plants from your garden/park or at least prevent them from going to see or spreading beyond the garden
  • If an invasive species is in a development site or where vehicles traverse the site, then cordon off where the invasives are, implement strict biosecurity to prevent inadvertent spread (Check, Clean etc) and remove or control the invasives.
  • Use responsible disposal for garden cuttings or pond plants – Be Plant Wise
  • Check purchased plants for New Zealand flatworms before planting in your garden
  • As always, remember to Check, Clean, Dry or Disinfect your books, water sport equipment etc when moving between
If you spot any of these invaders in your area take a photo if you can and let us know.

Click on the images below to find out more about some of the invasive species that are connected to urban environments and have been recorded in Ireland.

Harlequin ladybirds



Grey squirrel

Ruddy duck

Red-eared and Yellow-bellied sliders


New Zealand flatworm

Parrot’s feather

New Zealand pigmyweed

Water fern

Curly waterweed

Japanese knotweed

Giant hogweed

Giant rhubarb

Butterfly bush