“500 meters a month”

500 meters a month is how fast invasive crayfish can spread through an ecosystem, according to a report in The Guardian.

The Environment Agency said virile crayfish (Orconectes virilis), which are non-native, prey on native wildlife and spread crayfish plague, a disease deadly to native white clawed crayfish. The north American predators have recently been seen in waterways in east London after first being found on the river Lea near Enfield in 2004.

They have since colonised more than 10 miles of the river and linked waterways, spreading into Hertfordshire.

The agency has fitted small radio transmitters on the backs of the unwelcome guests, with preliminary results showing that virile crayfish are moving upstream at a rate of 500 metres a month.

This is substantially faster than their cousin, the signal crayfish, which is also non-native.

The Environment Agency report shows not only the two crayfish pictured above, but also notes that Lousiana red swamp crayfish (Procambarus clarkii) and Turkish crayfish (Astacus leptodactylus) are also present in the London area.

Hat tip to Kevin Zelnio.