Yellow Backed Bees

Anyone know what to make of these?

http://alexanderboyes.com/photos/201...llow_Backs.jpg

Context:
First year beekeeper just south of downtown Milwaukee, WI. Got a late start after two dud queens, but thanks to beesource member geebob I now have a healthy colony with a locally mated, first year queen. In early September I started noticing these yellow backed bees coming and going at the entrance. They behave normally, and I found them scattered throughout the hive. The pictured frame had more "marked" bees than most.

Is someone marking them? Are they marking themselves?

I too have these "marked" worker bees all over in my hives, especially earlier in the summer. I thought it was just pollen. I'd like to hear what others have to say.

Last Saturday I noticed bees coming and going at the entrance of one hive with yellow backs. When I opened the hive I saw numerous bees with the same phenomenon. I have never seen this before, and it was just in that one hive. I'll try to get a picture next time. I assume they are working a pollen plant and its adhering to them, but its strange in that the bees aren't really dusted yellow as they are sometimes. Its like its painted on their backs in a clump.

That's interesting. Maybe it's some kind of fungal growth or maybe their backs are picking something up when they pop their heads down into cells. Have never heard of that before though.

A thought: Around the time I started noticing this was when they were filling in a box of foundationless/starter strip frames. They were building sideways and joining frames so I had to do a bit of cutting and trimming on some freshly filled comb. Maybe their backs got sticky while walking the adjacent frames, they went foraging, and pollen stuck and hardened in place? Seems like a difficult place to reach with bee arms.

Somebody is marking your workers to determine where and how far your hive is from them.

[edit to add]

It's likely somebody raising and marking queens too. Since this is the 'yellow' year. Looks like they've been marked like you would a queen although rather sloppy.

It does look like they are painted yellow and I thought of that. However, they wouldn't have to mark my bees to detemine how far they were from them if they already knew where my hives were located now would they.

@Riskybizz

It would just depend on what they are tryna do.

looks like pollen... some flowers are set up so when a insect lands on them the anthers tag them, on landing on another flower of the same type the pistil must be passed in such away as to deliver the pollen. Not going to clean that pollen off with out help from a sister...

What I've heard...
Flowers of some plants snap the bees on the back when they dig down to get the nectar from it. Some flower in your area, blooming this time of year, is shaped such that the bees get snapped on the back when getting their stores of nectar from the plant.

Most likely it's pollen from Jewelweed.

Looks as if they are getting ready for trick-or-treats. ;)

I've seen them heading out to forage with the marking intact. If it were pollen wouldn't it be harvested and stored before they left?

I'll be back in my beeyards this weekend and if the weather cooperates. I'll try taking a few close up pictures and inspect the yellow bees more closely. Maybe try to remove the yellow with my finger. I have to admit it kinda has me stumped. I have seen many colonies with pollen covered bees looking like they were 'dusted" but this is different. I'm sure MP is correct in that its pollen from a collected source.

Maybe Beelining.
http://en.wikipedia.org/wiki/Beeline
Seems to be a sport with contests and all.

I am pretty sure it's pollen. My bees have shutdown now, but some had the same markings a few weeks ago.