noun

• (entomology) A genus of hunting wasp
  "Alastor eriurgus. . . A very common "mason wasp" in the neighbourhood of Sydney; very plentiful in February and March. They are subject to the attacks of cuckoo wasps and other parasitic Hymenoptera; in one nest I found a small Bracon larva beside the young Alastor, which it soon devoured, and then spun an elongate white silken cocoon, out of which it emerged ten days after; . . . I have bred out several specimens. These inquilines are placed in the Alastor nest while the builders are out hunting for caterpillars, their active mothers being on the watch to crawl in and deposit the eggs in the owner's absence."

name

• (Greek mythology) Any of several characters in Greek mythology, variously spirit, human, a horse of the underworld.