Invasive species - Snapshot Science

An invasive species is
one that has been
introduced by humans
to an area that it does
not live naturally.
Invasive species cost the UK £2 million
a year to monitor and control.
Is this a good use of money?
© Snapshot Science, 2010
Your task:
For each animal, award a score out of 5 for each criterion:
(0 = no known impact to 5 = maximum possible impact)
Predation and competition – do they prey on native animals,
or compete with them? How many different species are affected?
Transmission of diseases – do they carry diseases which can
harm other animals?
Impact on agriculture – do they damage crops?
Distribution – how much of the UK have they invaded? (the
dots on the maps show locations of breeding populations)
Add up your scores for each animal to give an overall impact score
out of 20.
© Snapshot Science, 2010
American Mink
Significant population declines of
ground nesting birds and small
mammals have resulted from mink
predation. The European mink is
threatened by the American mink
through competition by means of
direct aggression. Little is known
about mink as a vector of disease
but Aleutian disease has been
found in a feral population.
Can inflict damage to free ranging
chickens, reared game birds,
fisheries (salmon farming).
Grey squirrel
In overlap areas, grey squirrel causes
the extinction of the red squirrel
through competition. Also carries
poxvirus, fatal to red squirrels but
benign to grey squirrels (and
potentially transferrable to humans).
Also cause damage to woodland
through bark stripping activity.
Potential impact on nesting birds.
Severe damage to trees by bark
stripping. They cause local damage to
fruit orchards and nut growers.
© Snapshot Science, 2010
Rose-ringed parakeet
Rose-ringed Parakeets can compete for
nest sites with native cavity nesters.
In its native range in India, rose-ringed
parakeet is considered one of the most
destructive bird pests of agriculture, for
example reducing maize yields. In
Britain, the species can damage fruit
trees and has been reported to have
reduced the output of a vineyard. Roseringed parakeets can carry diseases
that also infect poultry.
American bullfrog
Feeds, on and competes with, a
wide range of prey, including
amphibians, fishes, small
mammals, ducklings and small bird
species, molluscs, crustaceans and
insects. This affects populations of
native frogs, toads and newts.
American bullfrogs may carry the a
type of fungus which causes
spreads of the disease
chytridiomycosis to native
Canada goose
These birds are heavy grazers of
aquatic and waterside vegetation,
which is food for many other
There is concern that the presence of
so many large birds in close
association with people, for example
in urban parks, may be a health
hazard. Canada geese are suspected
of transmitting salmonella to cattle.
Their grazing and trampling on
farmland may cause major damage
to grassland and crops.
Harlequin ladybird
Harlequin ladybirds are larger than native
ladybirds and devour their larvae. They
also eat aphids, leaving less food for them.
During winter they gather in buildings and
can cause people allergic reactions.
Harlequin ladybirds are a pest of apple and
pear orchards. They feed on fruit causing
blemishing and an associated reduction in
market value. Harlequins aggregate in
clusters of grapes prior to harvest and
when crushed with the grapes the ladybirds
impart a disgusting flavour to the juice.
© Snapshot Science, 2010
Sika deer
Damage is due to ring barking,
trampling, erosion due to creation
of trails and reduction of water
quality in streams.
In Eastern Europe, sika play a role in
the transmission of a nematode
affecting bison, roe deer, red deer
and potentially livestock. Both bovine
and avian TB has been found in sika
Sika are a serious forest pest,
causing significant damage to tree
Chinese mitten crab
Likely to impact native invertebrate
populations in freshwater and marine
systems, through predation and
competition for space. Has the
potential to outcompete the native
white-clawed crayfish.
The Chinese mitten crab carries a
number of diseases that can affect
native fish.
These crabs may cause loss of salmon
and trout in commercial fisheries
because of predation or competition.
Images: Chinese mitten crab: Fera, harlequin ladybird: Remy Ware, others: GBNNSS