The honeybee brain hosts over 600,000 neurons, at a density higher than that of mammalian brains:
"Our estimate of total brain cell number for the European honeybee (Apis mellifera;
≈ 6.13 × 10^5, s = 1.28 × 10^5; ...) was lower than the existing estimate from brain sections ≈ 8.5 × 10^5"
"the highest neuron densities have been found in the smallest respective species examined (smoky shrews in mammals; 2.08 × 10^5 neurons mg^−1 [14] and goldcrests in birds; 4.9 × 10^5 neurons mg^−1 [16]). The Hymenoptera in our sample have on average higher cell densities than vertebrates (5.94 × 10^5 cells mg^−1; n = 30 species)."
Ants, on the other hand ...
"ants stand out from bees and wasps as having particularly small brains by measures of mass and cell number."
