Lots of Black Locusts (Robinia pseudoacacia) grow around here, esp. along roadsides and highways. It seems that as you drive along, you'll see one "clump" in full bloom and the next clump is almost bare or with barely a few leaves-and they in fact had more leaves two weeks ago than now. In some trees you see what appears to be spiderweb or cobwebish looking things in the crotches of lower branches.

Same thing with another tree, they appear to be Boxelders, where a week ago they had more leaves than now and now what's there are brown shriveled buds.

Is there a bug or bugs affecting these trees? Or a fungus?

Neither are particularly desireable trees but it looks ugly.