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.