Galls
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| Oak gall © SBF 2014 |
One of the great parts of late fall and
early winter is that we are able to get a new perspective on our
natural surroundings. The leaves have fallen, the light reaches
places it hasn't in months and there is a stillness that exposes what
has been there all along. A few weeks ago as we were raking our yard
I noticed many oak galls. Oak ball galls, or oak apple galls, are
spherical growths found on oak leaves. Galls grow in many shapes and
sizes on a variety of plants. They are caused by insects, generally a
type of wasp or fly. The round oak galls that I find in my yard are
most likely caused by the oak apple gall wasp, or
Amphibolips
confluenta. This small wasp lays its eggs on the center vein of
an oak leaf. The tree responds to a chemical reaction caused once the
larva has hatched and begins munching on the leaf. The leaf grows a
mutation around the egg.
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| Oak gall © SBF 2014 |
Some galls are troublesome to the plant, but
this type of gall is rarely harmful to the tree. This is the first
step in a fascinating life cycle. As the larva continues to eat and
grow, the gall grows too. When the larva is full grown, it pupates
and then eats its way out of the gall, emerging as a winged, full
grown adult. The cycle begins again.
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| Partial Oak gall ©SBF 2014 |
Another type of gall that you may have
observed is the Goldenrod ball gall. If you have access to a field
that has not been mowed, you can easily find these galls in the
winter months. There are many great informal and classroom
investigations that can be done with these galls. The goldenrod ball
gall is another spherical gall that grows in the stems of the
Goldenrod plant. This gall grows in a similar way to the oak gall,
but is caused by the larva of the spotted-winged fly, Eurosta
solidaginis. The fly lays its egg on the stem of the plant during
the summer.
When the egg hatches the larva burrows into the stem of
the plant, hollowing out a living chamber for itself. The plant forms
a gall around the chamber. While still a larva the creature chews an
exit tunnel for itself. It must chew its exit tunnel while still in
the larva stage as adult flies do not eat and therefore do not have
the mouth parts necessary to escape their childhood home. The larva
pupates, emerges as an adult and the process begins all over. I have
always found galls interesting. To read more about types of goldenrod
galls see this
article that I wrote several years ago for the Squam Lakes Natural Science Center.
You may also want to check out
this post that Sue at
Archimedes Notebook recently wrote about galls that she observed on her hickory
leaves. It includes a link to some other types of wild looking galls.
If you are interested in learning more
about Goldenrod galls specifically, as they are fairly easy to spot
this time of year, I would encourage you to check out this
interesting study at the American Museum of Natural
History's website. If you are a teacher or just an inquisitive
naturalist, you might want to try this
Goldenrod gall lesson from the Cornell Institute for Biology
Teachers, or this activity from Cornell for ages 12 and up:
"Exploring Plant Galls".
Happy gall hunting!
Have you made an awesome science observation this week? Comment below!
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