The Bees are mysterious, officially unnamed beasts that appear in Pikmin 2.

The Bees appear in the Wistful Wild on day 31, and every 30 days after that. This means Days 61, 91, 121, etc.

When attacked, they will disappear and release large amounts of Sprays, both Bitter and Spicy. As there are many 'Bees', you will end up having a large amount of sprays. They can also release poison in defense, so you might want to use White Pikmin for this in case you are a safety freak.

The Bees do not show up in the Piklopedia. They have no health bars and leave behind no bodies. Most likely, they were programmed in as an Easter Egg. Of course, it could also be a case of forgetting to make entries for the Bees...

It has been speculated upon that the Bees are some kind of Larva. Most of the time, they are being opted as being Shearbug/Shearwig Larva (due to their tuny size and apparent, underdeveloped Pincers) or Doodlebugs (due to their release of Poison and Sprays and having tiny legs). It's possible that they are Doodlebug larva who grow into Doodlebug size as their life progresses. They could be Shearwigs as is made apparent by tiny Pincers.

They could also just be their own, mysterious species...

Look at all those sprays and Bees!