The Trees aren't Empty.
The spiders up in the trees shoot ugly glances at passersby, except when the pedestrians throw coins to the hungry garden gnomes working slave labor in the inner-city parks. Occasionally, one of the spiders will jump down and pick up a bag of coins from a pre-determined check-point and deposit the chewed-up cash in a bank account under the name of the President's pet parakeet for nefarious purposes.
Every so often, the spiders will make a delivery of Spam to the gnomes, but the gnomes don't want to "Make Money Fast!" so they go back to their nuclear-powered treadmills.