What swarm do mantispidae belong to or are they even still around?
They are around! In fact, I had a whole character with an arc going into them that sadly had to be cut for time.
Mantidflies are parasitoids on spider eggs--basically, they crawl into a wolf spider's egg sac and live in there, eating the eggs as they grow.
As macrovolutes, mantidflies are considered changelings. However, Spider Swarm is eager to divorce themselves from the other arachnids and become more insect-like, and this close interplay of mantidflies with their own eggs (through means I cannot spoil) brings their bolecores closer to an insect's.
As a result, these "changelings" are not only accepted by the spiders, but openly embraced and even revered, even and especially by their spider "mothers." The average mantidfly tends to have an entitled, spoiled little princess/prince attitude as a result.
Of course, they're still treated as second class citizens by other insects. They do belong to Spider Swarm, after all, and the insects do not look highly on the arachnids...so, certainly, they do not regard the "spider insects" highly either.