Because pollen sucks.
It does! But if you prefer the smart word: itâ€™s hygroscopic. It attracts water.
And where is water, there is rot.
Which is a problem when you are an insect that relies on pollen to feed its brood and therefore needs to store pollen for weeks, if not months. You may be more or less okay when in a desert or at least able to avoid the rainy season â€“ but in our friendly fertile temperate zones, youâ€™re not.
Still, they are here. Plenty of them. Mason bees and leafcutter bees and carder bees and many more.
In their new paper, Christophe Praz and his colleagues suggest a scenario for just how this could have happened:
Before the bees began to feed pollen to their brood (i.e. before they actually became bees) they were something similar to todayâ€™s apoid wasps (Grabwespen). They were hunting other insects, paralysed their victims and dragged them into the broodnest where their prey would stay alive for several weeks before being consumed by the larvae.
You may find this disgusting or not, but keeping your food alive until consumption is definitely a good way to keep it fresh.
And there is nothing â€žprimitiveâ€œ or old-fashioned about it. There are still plenty of wasps around who do exactly this. But this method does have its costs. Hunting takes time, itâ€™s not without risks, chances to find prey are limited and so on. So when the flowering plants arrived and offered pollen as an alternative source of protein, the beesâ€™ ancestors skipped their carnivorous habits and became all out vegetarians. Which â€“ as we all know â€“ turned out to be a smart move.
But before the flowers and the bees could become one of the biggest success stories on the planet, there was one more innovation needed.