Looking for Lacewings in Unusual Places

It really surprised me to find this clutch of green lacewing eggs (Chrysopa sp) in a very prickly spot. Lacewing larvae feed on small arthropods; they are considered highly beneficial in the garden as they keep numbers of plant pests such as aphids in check. I saw a lacewing larva feeding on Pittosporum psyllids, deep inside the folds of the damaged leaves where few practical control measures could go (save systemic insecticides).

Anyway, what prey is likely to be found on this cactus plant?