So the land to the east is a treacherous land of death. While a shame to have lost so many of the expedition, at least their sacrifices were not in vain.  

To the big problem we now have to deal with: The threat of larger creatures and the damage they can do both to our hives and our food sources. 

Mandibles have worked nicely against creatures relatively our own size, but they prove ineffective against these giants that besiege us. Might I recommend a new warrior breed inspired by the snakes and spiders we have encountered in the past; Rather then mandibles, we need a number of warriors to develop fangs/stingers instead. A means to punch into a larger, fattier target in order to deliver a shot of our venom deep where it will do the most harm. 

A second suggestion to go with the first: Taking another bit of inspiration from the Spiders, the venom employed by these anti-giant warriors shouldn't be paralytic; Instead, it should work to melt skin, muscle and fat into a liquid in order to maximize pain to ensure that the target gets the message that coming near us is a bad idea. 

Alternative means of dealing with large predators: Instead of Mandibles, equip new breed of warriors with some means of borrowing into the target's flesh to eat them from the inside out. Can also be used as a means of ensuring that venom delivery reaches vital areas.