In the world of this question, ants and especially termites are the dominant herbivores by mass. There are no large grazing mammals competing with the bugs for the siliceous grasses and thorny trees of the savanna.
The dominant (by mass) food chain on the savanna's of our Earth is grass->antelope->lion. I would like a longer food chain with more steps, similar to that in the ocean (phytoplankton -> zooplankton -> small fish -> larger fish -> shark).
In order to make this happen, I need small lizards, birds, and/or mammals to be the primary (again, by mass) predators of the ants and termites. But on our Earth, ant eaters are big: anteaters, aardvark and sun/sloth bears are the dominant insectivores of the savanna regions. Larger animals have some distinct advantages; namely, while 10,000 ants can kill a shrew, they can't do much to a bear.
What evolutionary pressures would favor small (1 kg or less) insectivores over large ones in an ecosystem dominated by ants and termites?