Wending my way to the Earley Gate on the evening of Thu. 13th, I found a small plant of Creeping Thistle (Cirsium arvense) in grassland with Lady’s Bedstraw (Galium verum) not far from the Psychology building. What caught my eye was a swelling in the thistle’s stem about 3/4 of the way up. I’ve seen similar swelling on thistles several times before but this time I was inspired by the `Galls on Campus’ blog to investigate further….
The gall (if such it be) was a “prolate spheroid” (like a little rugby ball) approx 2 cm long and 1.5 cm across. I took it home to look inside. Just below the soft, green surface it had an amazingly tough, hard and woody shell (protecting the content from birds?) With a lot of pressure I managed to section it with my penknife.
The white splotch at about 8 o’clock from the centre of the gall was a fat, pure white maggot with a clearly-defined head. The body was a couple of mm thick but also only a couple of mm long…I fear it may have been sectioned along with the gall. So, any ideas? Is it a gall-insect? If so, which one?