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."
A huge factor are eyes. Bees and wasps have large eyes and this requires more nervous system to support them.
But also, they have included ants of various sizes, tiny ants, big ants... but not tiny wasps? The ones who have the smallest functional brains of all.
On fairy wasps, they do include them. This is what they write:
"In the small Hymenoptera, neuron size may be a limiting factor for brain miniaturization, as shown for the smallest insects (the parasitoid wasp Megaphragma [42]), whose larval brains comprise less than 5000 cells, the cell bodies of which are lost during pupation. The brain of the smallest species in our sample (the parasitoid wasps Leptopilina; figure 1) comprised around 30 000 cells (electronic supplementary material, table S1). Similar neuron numbers (2.2 × 105–3.7 × 105 neurons; [43]) have been estimated for fairyflies (Hymenoptera: Mymaridae), which are smaller than the smallest of our samples, suggesting that our cell number estimates may be conservative."
On ants: ants have large antennae and use them for all sorts of tasks, including sensing wind, scent, and mechanoreceptively as if they were hands but also as drums for assessing through vibration the content and properties of what they are touching. Parasitoid wasps ("flying ants", sort of) use their antennae to drum surfaces, a form of active echolocation of caterpillars and larvae inside plant stems or wood. All of these activities need a lot of brain power to process them.
Granted, eyes as 2D surfaces require lots of repeated neurons for contrast and color, and neurons that integrate across them just to process movement in the visual scene. I'd like to see a comparison with the size of antennal lobes and AMMC (antennal mechanosensory and motor center) regions of wasps and ants.
OK I didn't understand one of the graphs in that paper at all then! (that's what I get for skipping to look at the graphs)
There is something remarkable going on with hymenopteran brains. There are issues too like lifetime variability. Queen ants on their nuptial flights have the biggest ant brains. Their brains shrink when they transition to a focus on staying inside and laying eggs.
@futurebird@albertcardona makes sense flying and visual processing during flight might take a lot of brain power. they reabsorb flight muscle, y not reabsorb flight neurons! mek mor bebbes!
@albertcardona my hypothesis for why they can achieve a higher neuron density would be that because the brains are smaller, nutrients and such do not have to travel as far into it they need less gaps to supply the cells further into the center.
would be interesting if this holds up for any (or at least most) creatures brain size in relation to its neuron density.
and could this relation be estimated with some linear, or i assume more likely a logarithmic or exponential function?
Regarding nutrient and oxygen flow, would be interesting to compare the brains of a large bee like Xylocopa violacea (violet carpenter bee [1]) with that of a small bat like Craseonycteris thonglongyai (bumblebee bat [2]).
These two species are of about the same size (3-5 cm), yet one is an insect and the other is a mammal. Actually, the bee is larger than the bat! I wonder which one has more neurons.
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