Asilidae are robber flies. Some species catch their prey in flight. Some catch prey on the ground. Just like spiders and some other arthropods, they use a neurotoxin, which they inject into the squirming catch to subdue it, and an enzyme to help digest the internal organs and some muscles (apparently, many muscles in the legs and other distant areas from the injection site are left behind).
This particular robber fly likes the top of a foldable cage that I have for my small tortoises. I have seen this one... or perhaps a few of its friends sitting one at a time in the same place (?), sitting waiting for something delicious to come by. The large red dragonflies (Anisoptera) that buzz the Gulf Fritillaries (Agraulis vanillae), have special tall reeds to alight on to either survey territory or to look out for food.
Here is another naturalist fro last year, with another robber of a different Genus.