Fogot to say that these photos were taken in August on Zanzibar.
It's a Spider Hunting wasp - Hymenoptera: Pompilidae. It's doing exactly what it says on the tin and appears to be wrestling with a spider. This group of wasps specialise in spider prey - females sting and paralyse spiders before dragging them back to their nest burrow where she lays an egg on the spider that is destined to be food for her larvae. You can also witness this from our native UK pompilids in the summer months.