Did you know some insects make homes in a flower stem?

Most flower stems are smooth and narrow, providing a long, straight path for the leaves and flowers it bears. But sometimes, if you walk through a field of goldenrod, you find something different. Some goldenrod stems have large balls on them, a little like the knob on a sceptre.

That knob, or gall, is actually an insect’s house!

What kind of insect depends on the shape of the gall. If it’s round, it’s the goldenrod gall fly, and if it’s more oval, it’s the goldenrod gall moth!
The galls work the same way for both species: the mother lays her egg on the stem of the goldenrod, and as soon as the baby hatches, it eats its way through the stem and hides inside. The goldenrod gets irritated by having the insect inside it, and responds by building up a thick layer of plant tissue that protects and feeds the larvae.

When the larvae is ready to pupate, it chews itself a tunnel to the outside of the gall. Then it returns to the centre to change into an adult fly or moth. Once it gains its wings, it crawls through the tunnel and flies away!

But sometimes the gall doesn’t protect the larvae so much as give away its position. Some predatory invertebrates, like wasps and spiders, use the insect in the gall as a food source for their babies! One wasp lays her egg on the larvae inside, so that when her baby hatches, it eats the moth or fly larvae!

If you open up a gall in the spring, what you find inside can tell a whole story about the tiny creatures that called it home.