Leaf miners and Gall Wasps
As we continue to go through a rather dry winter, with only very few flying insects, blooming flowers, refreshed lichens, mushrooms and mosses to observe, two groups have left their marks of which some are to see year round: leaf miners and gall wasps.
There's a great project on leaf miners:
https://www.inaturalist.org/projects/leaf-mining-insects-of-california
Some are easy to ID as their host plant is part of their English name. Examples we should be able to find:
Toyon Leafminer, https://www.inaturalist.org/taxa/469764-Stigmella-heteromelis,
Poison Ivy Leaf-miner, https://www.inaturalist.org/taxa/215950-Cameraria-guttifinitella,
Morning-glory Leaf-miner moth: https://www.inaturalist.org/taxa/214958-Bedellia-somnulentella.
We have 43 Oak Gall Wasp species in Los Angeles County:
https://www.inaturalist.org/observations?locale=en-US&place_id=962&preferred_place_id=1&subview=grid&taxon_id=205775&view=species
Some have dropped off their hosts by now or are so shriveled and dry that they are really hard to find, but a few are observable even now.
In my (limited) experience, if I can see an oak apple in an oak, chances are other gall wasps have used that tree too.
As to IDs, noting the host plant (and/or including pictures of the host plant) seems to be essential for the ID.
Any other tips?
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As I am pretty new to looking at these organisms, I can't really add much. Having said that, I have been looking more closely for each of these organisms lately and it does add a new angle when I'm out and about. In fact, today, I decided to specially walk over to Los Encinos Park since I knew there would be oaks to examine and I wanted to see if I could find any galls that were new to me even though it's late in the year and not so likely. I would point out that parks are not an awesome place to look for galls simply because the trees are shaped to be a bit higher than a human head. I did find a few low hanging branches and some young trees along the edges, but not much luck on the galls. I posted two observations today and didn't bother with another pumpkin gall I saw as it a bit too high for a good photo.
The leaf miner project Andrea linked has some good tips on photographing for ID and I thank you for that, Andrea. As she mentioned to me earlier, the hunt is on...
Hope you all are staying safe and healthy.
Thanks for sharing these Andrea! I often look for galls but it seems that many are difficult to find. I seem to see the same ones over and over. I see a lot of those leaf miners but have only posted a couple. One thing I’m finding is that the galls seem to be more numerous when the habitat is in better shape. The drought is having a really dramatic affect on everything right now. Regardless this is great info to have.
Interesting guide to SoCal oaks and their diseases:
"This reference guide was developed to provide an overview of common injury symptoms from insects and diseases to oaks in southern California."
https://ucanr.edu/sites/gsobinfo/files/63838.pdf
From USDA: A Field Guide to Insects and Diseases of California Oaks
https://www.fs.fed.us/psw/publications/documents/psw_gtr197/psw_gtr197.pdf
On Friday, I found five different galls, crown whiteflies and a leaf miner (plus a Green Lynx Spider) within an hour of combing the trees on "Secret Trail," just up the street from my house. I wanted to continue on the narrow trail, but returned home via a side trail when a group of unmasked hikers was approaching. This used to be a very quiet neighborhood trail, but it suddenly became a destination and is now littered with dog poop or best case bagged dog poop... When I started there was only one car parked in the tiny lot. When I returned there were five. The habitat in this spot is in comparatively good shape, the creek even has a tiny trickle of water. And some of the trail is on a steep slope which makes oak leaves more accessible. Recommended during the week.
One day I'd like to explore "Secret Trail" which isn't se secret after all :)
Thanks for the links above, I spent some time perusing the USDA field guide and there are so many more little insects we can try to find on our oaks and other trees. I rarely take the time, but now that I know a little more thanks to you all.
Anyway, low tides right now and I feel the beach calling...
Thanks for this great info. It’s good to learn about all these things. Finding them will be somewhat of a challenge but a good one. As for the trail, I find that almost every trail is worse than before the pandemic. People are everywhere and it’s disheartening. Glad to hear there is a bit of water on the secret trail still.
I just stumbled upon the most amazing and comprehensive resource for California galls, both on oaks and on other plants... Where I found it, you ask? On iNat, of course.
https://www.inaturalist.org/projects/california-plants-with-mystery-galls/journal
There's also a sister project with more infos, https://www.inaturalist.org/projects/galls-of-california.
There is so much info here, thank you. I took a quick gander, but this will require some devoted time to looking up some of these more closely. We should make a list of some we might be able to find around here that we haven't seen yet.
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