Still in lockdown I have been mulling over the overarching Siberian elms that grow from my neighbour's yard. The mystery was that I knew the tall trees were raining down some sort of "sap" onto my wife's car. She moved the car out from under the canopy. First off, I noticed the "sap" was water soluble, because a quick wipe of the windshield wipers removed it. This meant it wasn't sap, like the pine trees produce. I thought it might be from the sprinkler system, but a quick look around the car showed a concentration of spots more above than below and on all sides equally. Also there was no rain spot rings of mineral deposits.
I didn't give it much more thought until I started wondering why the numerous species of ants were so excited in the early evening to be moving around our concrete porch, they were really checking it out. There is no food out there, and they were more interested in the bare concrete than the gravel around it. The clincher was watching the flies slurping the residue off our gate that is under the trees.
So I had to research. I do not like plants, they are far too technical for me and have nothing to do with frogs. However, initial research in PubMed shows that elms trees in Albuquerque (Ulmus pumila) are raining down a veritable chemical factory. I thought it was just sugars. I knew about all the compounds that ward off foraging animals, but I had never heard of synamones a class of substances put out to attract predator insects; known as chemical ecology. The mystery of what the attractant here is persists, but maybe one day I'll have an answer...
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