Monday, August 18, 2014

Robin's pincushion gall

Today I found this strange thing on a rose bush in our backyard. Upon closer inspection it turns out that this structure was grown by the rose as if it had forgotten how to make a leaf, a thorn or a stem.
It is called a gall and if you cut it open and look inside you'll find a couple of small chambers that are home to a bunch of larvae. The gall provides food and shelter for these growing insects.
Galls are usually the plant's response to an injury or a foreign object, such as a small animal.
Once a larva turns into the adult insect through metamorphosis it looks like the image on the left. This is a rose gall wasp with the scientific name Diplolepis rosae.

Gall formation is not entirely understood, but it is more than just scar tissue. The insect or mite in the gall apparently causes the plant to form a gall by releasing chemicals that change the plant's growth program.

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