This Fall Kyri learned about wasp galls in one of her Nature books. Ever since then, she has been fascinated with them! When we are exploring outside, she makes it a point to look for them. We spent a fair amount of time this weekend collecting wasp galls and cracking them open. It was so interesting to see what was inside each one!
But first, a little background on galls…
A gall is an abnormal growth on a plant. Some plants will produce these growths on their own, but often their formation is induced by insects.For many kinds of wasps, these formations provide nourishment and shelter for the developing eggs.
The female wasp inserts her eggs into the tree’s tissue, along with a chemical that induces this abnormal tree tissue growth. A gall is essential an abnormal tissue growth on the plant, like a tumor. The egg grows and develops within the gall, which serves to protect the wasp larvae. When it matures, it will chew its way out of the gall. The empty gall is then used by other species for shelter.
There are two “generations” of gall wasps that emerge from these galls. In late December, there is an “asexual generation” so only adult females emerge from the galls. Adults of both sexes emerge from galls in the “sexual generation” which occurs in early Spring. Eggs layed by the sexual generation will lay dormant for several months before emerging from their galls as the subsequent asexual generation.
The wasp larvae are still susceptible to predation even within the gall’s protective casing. But here’s an interesting fact – the developing larvae produce a chemical that converts the plant tissue (a starch) into sugar. This sugary secretion, called honeydew, attracts insects such as ants, honeybees and yellowjackets. These insects discourage other predators from going after the larvae inside the gall.
Here are some links with more information.
The branche of the live oak on our property have a multitude of marble-sized galls. I happened to point them out tomy husband today and told him about Kyri’s fascinationg with them. He was curious, and he happened to have a hammer in his hand, so he picked one and we cracked it open. Kyri was all about cracking open galls so we spent a good while picking galls and opening them up. It was quite an educational experience for the family.
Within each gall we found a yellowish casing, presumeably for whatever type of wasp formed the gall in the first place. We found each of the galls contained a yellowing casing which we assumed was from the wasp larva. Each gall had a pin hole, which was assumed to be formed when the larva chewed its way out of the gall.
We did not find any galls that contained wasp larva, only the remaining egg casing. However, many of the galls we examined did contain small spiders, or spider silk and spider eggs. The gall is an inviting home for spiders to lay eggs and settle in once the wasp larva are gone (or while they are still in there). Several of the galls contained mini colonies of ants. This was not expected (we didn’t know much about the ants before our “field work.”