No, it’s not a miniature oil slick. That oily film on the surface of puddles on The Lizard is an iron-oxidizing bacterium.
Photo: Amanda Scott

 

 

Scientific name: Leptothrix discophora

What to look for:

· Colouring and appearance: Oily-looking film on surface of puddles on heathland. Breaks up into small plates when touched, rather than swirling like oil.

· Where: Globally, in habitats rich in iron

While wandering across The Lizard’s heathlands, have you ever puzzled over the oily film you can see in puddles on the trackways or on still water between clumps of vegetation. It is not a case of someone being careless with an oil can: this is acutally a bacterium – Leptothrix discophora – one of a group of different species of bacteria that survive by oxidizing iron and other metals. The film you see on the water is created by the bacteria (which are themselves microscopic and therefore not visible to the naked eye). If you want to tell it apart from oil, gently push a twig through the surface (it will not hurt the bacteria). Oil will swirl, whereas a L. discophora film breaks up into tiny separate plates. You can see this clearly in the lower image on this page.

Published: April 2016
Author: Amanda Scott
Photos: Amanda Scott