Film on truck, parked under oak tree

[lucky8926]

There's a large oak tree beside my driveway where I parked my truck. It seems the spring and summer the tree sheds something, not really so much of a sap but it just leaves a film on my truck. It cleans up fairly easily but I'm just not sure what it is. I read one article that said that it is insect droppings. Anyone have any idea what it might be?

[Don M]

Probably just tree sap, but still I would maintain a good wax/sealant on the car and wash it often to prevent damage to the paint. I tried to get sap from a tulip tree off a minivan once, it was like trying to remove big blobs of super glue & I never did get it off.

[lucky8926]

I don't think it's sap, it's not sticky at all and fairly easy to remove. Plus is under an oak tree, I'm not sure but don't believe they drop sap.

[Lost Highway]

Aphids secrete a substance euphemistically referred to as "honeydew." I don't tend to see quantities of aphids on oaks but then there are many species of oaks (and aphids) and it isn't like I'm spending much time in the canopy of oaks forty feet off the ground. It could be another insect but my first guess would be aphids.