  An important feature of Schwarzschild spacetime is the presence of orbiting
null geodesics and caustics. Their presence implies strong gravitational
lensing effects for matter and radiation, i.e., for excitations of quantum
fields. Here, we raise the question whether the lensing manifests itself also
in the vacuum of quantum fields, namely by lensing the distribution of vacuum
entanglement. To explore this possibility, we use the method of entanglement
harvesting, where initially unentangled localized quantum systems are
temporarily coupled to the field at different locations. We find that for the
Boulware, Hartle-Hawking and Unruh vacua in 3+1 dimensional Schwarzschild
spacetime, the harvesting of vacuum entanglement is indeed greatly amplified
near caustics. In particular, we establish that pre-existing vacuum
entanglement can be harvested also for lightlike separations.
