Tuesday, May 8, 2012

Bees that dig holes in the ground - Miner Bees, Part III

Our mining bee homeschool science project

   I thought the kids would enjoy digging into a bee's underground nest. Who wouldn't want to know what is down in those dark holes behind the little sand piles? 

  We cross-sectioned a burrow to learn about the nesting habits of the mining bees and also to learn what provisions the bee gathers for its larvae.
In the photo below, a cross-section of the bee's tunnel is visible above the trowel.
   Digging along the tunnel without destroying it was a real challenge because the tunnel took a few turns and there were a few obstacles like roots and pebbles in the sandy soil.  The bee's burrow went down about a foot before leveling out and ending in the brood chamber.  See the exposed tunnel in the picture below.
   The white "plastic bag" at the lower right of the photo is the brood cell liner.  I was surprised to find a lining in the brood cell because I thought we were digging out a miner bee's burrow.  Miner bees (Andrena spp) do not make a cell liner quite like this.  I obviously had jumped to conclusions on the identity of these bees.
  The burrow we profiled was made by a Cellophane Bee (Colletes).  Cellophane Bee brood chambers are lined with an amazing polyester cell liner... a plastic bag... that holds a mixture of nectar and pollen to feed the bee's larva.
   In my two previous posts on these bees, I called them Miner Bees but I didn't look closely at them before I made that assumption.  I should have made one of the bees stick out its tongue and say, "Ahhhhh". Cellophane Bees have a bi-lobed tongue, while miner bees have a pointed one. Also, there is a difference in their wing venation.  On the wings of Cellophane Bees, the second recurrent vein curves toward the wing margin.

 Compare that Cellophane Bee with a photo of a miner bee I found nectaring on some flowers on a nearby mountain.  On miner bee's wings, the same vein is straight.

  Brood cell lining of the Cellophane Bee.

   When we carefully dug along the Cellophane Bee's tunnel, we found that the bee had made multiple brood chambers about a foot down in the ground.  We also noticed that the tunnel levels out just before the brood cell.  These nests ,with their polyester liners, were always tilted at a certain angle like the one pictured below.
   Notice the small amount of the nectar/pollen mixture the bee has gathered and placed in the newly made nest liner.  The finished bag will be mostly full of food stores for its larva.  When the  bee is finished filling a bag, it lays an egg and attaches it to the upper part of the neck of the liner.  Then it plugs the opening with what looks like glued together sand.
   In the photo below, a young Cellophane Bee is peering out of its polyester home where it has been growing since last spring.  It's all there... the new bee, its brood cell liner, its plug, and even some of its food stores.  Soon it will venture out... stretch its wings.. etc.

   When the Cellophane Bee makes its "plastic bag" nest liner, it first lays down a mesh of silk and then coats it with the polyester.  The "plastic" forms when the bee mixes saliva with a secretion from its Dufour's gland which it applies over the silk fibers.  In the photo below, the silk fibers embedded in the polyester liner remind me of fiberglass and resin.
   We did an experiment to see if the brood cell liners are waterproof...  I filled the "little plastic bag" with water and held it up to the light.... look guys, no leaks!
Simply amazing!
   I guess you could say we unearthed a subterranean factory where fiber-reinforced plastic bags are manufactured.  Another way to look at it is; the bees bury barf bags to feed and house their babies.
Anyway, digging bee's nests was quite entertaining!
Shhh... digging the bees was also educational!

Part I of the Miner Bees


  1. Hi, Dana. I've been reading your posts about miner bees with great interest. I have quite a colony of some sort of ground bees in my yard, and your information about miner bees has been helpful to me. The bees have been here for several years and each year there are a lot more of them. They appear in late March or early April when the air and ground begin to warm (I'm in the southeast corner of Tennessee) and they usually disappear sometime in June. The first year I noticed them there weren't very many but now I believe I have hundreds if not thousand. The yard looks like a bee war zone. Individual burrows, like you described, several in each square foot of yard, cover hundreds of square feet. My boots get muddy when I try to mow the grass, which I can only do early or late while they are asleep / much less active. I've never been stung, but I have been tapped, sort of like being dive-bombed by a bird protecting the nest. They live adjacent to my garden and blueberry patch, and I am so thankful for them because they are fantastic pollinators. I must admit that it has never occurred to me to excavate a bee burrow, and I haven't tried to examine wing structure. I'm allergic to yellowjacket and bumblebee stings, so I'm not close enough to inspect, but I do walk among them.

    1. Audrey,
      Thanks for commenting. I can imagine what your yard looks like! There are parts of our yard in which the earthworms have done something similar. I have noticed a few bee mines on our river bank.
      Here's a link to a nice overview of our native bees. http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5306468.pdf The article mentions buzz (sonic) pollination (for your blueberries). I'll venture a guess that the ground bees use that same sonic action to act as vibratory packers when they are tunneling. Perhaps you've heard them buzzing in the ground?
      Another interesting thing about these bees (Halictid, Andrenid, etc)is they have a commensal association with nematodes. See this paper... http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2619032/pdf/150.pdf
      Your yard has a subterranean city of bees and their nematodes. Wow!

  2. Fascinating post Dana.

    Wow that's a huge chamber at the end of the tunnel. I really enjoyed learning about the larvae feeder bags.

    1. Sybil,
      I enjoyed reading a paper that describes in detail how the Cellophane Bees made those bags. The researchers observed the Colletes nest building process in glass tubes. The paper's title begins, "The Nesting Biology Of Colletes..." Here is the link. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1109&context=entomologyother