Groetaw

The Weinadi have, perhaps, less to fear from the skies than they used to, but the weather and the groetaw remain a constant struggle.

— Quote from a letter from the tribes to someone in Tholaren Dome

While the Garruw were the primary predator of the Weinadi for a long time, as that threat eased, another remained. The groetaw are not a sentient species, not capable of higher level thought or negotiation, and so they continue to feed where they can.
They are strange in appearance compared to the Lafgej or the garruw, but they nonetheless take to the skies like those other two species. They are serpentine in appearance, long and slender, with a number of spines along the length of their bodies.
They fly, but not by using wings. They possess a kind of bladder that they can fill with air, and they have something like flaps that they use to control their descent. They have a difficult time getting aloft during low storm season, but at full storm season they are something of a terror. Their spines catch the lightning and dissipate it harmlessly along their bodies.
When forced to ground, they slither like snakes. Their trails on the ground are quite obvious. Even the garruw attempt to avoid them because their spines have a venom that is most effective against them, merely stunning a weinadi. In any ordinary fight, they could easily defeat the groetaw, but the creatures like to swarm in packs.
They stay well away from human settlements. There is presumably something about their technology that deters them. When given the opportunity well away from civilization, they pounce easily enough.