September 22, 2021

I, Science

The science magazine of Imperial College

American signal crayfish
American signal crayfish

Alien species are having a massive impact on the UK both in terms of our natural ecology and our economy.

Not actually little green men, alien or invasive species are types of plants or animals that aren’t native to an area but have somehow been introduced by humans. Whilst there are a few notorious aliens that the majority of people are aware of such as the grey squirrel, many are wreaking havoc around the UK without most of us batting an eyelid.

One such unwelcome resident is the American signal crayfish, a pretty sinister looking alien that does not come in peace. Signals were first introduced into our waters in the 1970s but caged safely inside freshwater farms set up to supply the restaurant trade. Not surprisingly it wasn’t long until a few individuals escaped and began a relentless invasion of our lakes, rivers and streams. There are now millions of them.

Unfortunately Signal crayfish are aggressive predators that will make a meal of pretty much anything from small fish and their eggs to aquatic plants and invertebrates. They also carry a nasty disease that has all but wiped out the white clawed crayfish, a smaller and less aggressive native to our waters. On top of devastation to the locals signal crayfish also dig deep burrows in the side of streams and river banks. These burrows can cause banks to collapse and at times of high rainfall this inevitably leads to flooding.


Signal crayfish are not our only aquatic aggressors. North American floating pennywort is clogging up our rivers and American mink are devouring native endangered species like the water vole. Back on dry land the invasion is in full force with super weeds such as Japanese knotweed suffocating local plants, and the harlequin ladybird feasting on rare butterfly and moth larvae.

So far scientists have identified around 11,000 alien species established throughout the UK and the government estimate that they cost the country 2 billion pounds per year in control and damage costs. Most of them are also a major threat to biodiversity.

So what is actually being done to thwart nationwide alien domination? Well across the UK environmental government bodies are already tackling some invasive species. Trapping of American mink is well underway and herbicides are being used on harmful populations of knotweed and pennywort. Sadly many aliens are proving difficult to eradicate including the signal crayfish. No effective approach has been found that weakens numbers of signals yet but researchers are working on new strategies involving the introduction of sterile males into waterways.

In light of the cost to the environment and economy much more really needs to be done. With the coalition declaring they are the greenest government ever and the UN Convention on Biological Diversity meeting coming up in October, it may be that we see more strategies put in place to deal with invasive species over the coming months.