Monday, 8 September 2014

Thistle amaze you

 
I saw this swelling on a thistle stem today at Filnore Woods.  Looking it up I discovered it is a gall caused by the Thistle Gall Fly (Urophora cardui).  The eggs are laid in the thistle stem during summer and a fat brown grub develops.  The thistle supplies it with food by growing this gall.
 
I've never seen this fly but found a picture of it on the NatureSpot website.  Thanks to photographer Barbara Cooper for the image below.
  
 
These clourful little flies are about the size of a house fly and are around between May and September.  The larvae grow inside the gall and overwinter inside it.

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