Nature Blog Network

Tuesday, November 17, 2009

The Gall of that Fly.

Goldenrod galls are probably not the most common around here, but due to their size and relative common-ness, they are definitely the most "famous," and when I say "gall," this is what students think of. The sketch above shows what they look like this time of year -- I love that the leaves (now just little nubs where leaves used to be) continue to grow out of the stem where the gall is... These galls are housing flies, which spend nearly a full year inside the goldenrod stem, if they are not interrupted by a mean teacher with a pocketknife. The adult flies, with a lifespan of less than a month, mate in the warm months of the year. They lay eggs inside of the goldenrod stem, and the larvae begin eating the stem immediately upon hatching (10 days later). Their saliva contains an enzyme that causes the plant to the protective gall. The plant functions around it, and the insect is completely protected. As it eats, it makes more space to grow and puts down more saliva, causing more stem swelling. As winter approaches, the gall flies dig a tunnel almost to the edge. In the picture below, you can see the the larva in the very middle, and the tunnel it has made going up between 1 and 2 o'clock. But it won't finish eating its way out until the spring... over the winter, it will stay in its protective plant case and produce some anti-freezing stuff. When spring arrives, it will pupate and emerge through a hole in the gall.
ps -- never rained yesterday, now they're saying today...


  1. This is a brilliant explanation for what may be the most-asked question on the prairie...."What is that thing?"

    Lovely drawing as usual!!