[AllenG (OP)]

There is a spider in my yard that has spun a web anchored to trees that are about ten meters apart.
Is this animal dragging a line from one tree to the other or does it use another method to attach its silk between the trees?

[paul.fr]

I think they "run out" a length of silk and then use the wind / breeze to carry them over to your second tree. This is also one of the reasons a spider can not escape  from a bath...no current for the line of silk to float on...possibly!

[Don_1]

I have seen spiders doing this in my back garden (yard if you are USA). The silk thread is attached to something stable and the spider slowly lets out more thread. It splays it's legs and is carried on the wind like a kite. I think it's mostly a case of ending up where the wind takes them, but I think there may be some control over it's direction and altitude by the attitude of the legs. Very cleaver maybe, but I still don't like spiders.

Little Miss Muffet,
Sat on the tuffet,
Eating her curds & Whey.
Along came a spider,
Which sat down beside her,
So she trod o the hairy legged little git. []