Miscellaneous Findings Through Pollen Microscopy

Honey bees are known for their floral fidelity, meaning they consistently visit flowers of a single plant species during each foraging trip. In fact, it was rare (less than 0.4%) to find multiple pollen species in a single pollen chunk. This number may be an underestimate, as some pollen species are indistinguishable by shape.

Below are a few examples of mixed pollen samples found in my hives.

In summer 2019, I had two hives with similar strength. They showed remarkably different foraging preference in the period between 6/1/19 and 6/10/19, as shown below. All these plants could be found within 1500 ft from the hives.

Hive 1 (73 specimens): Blackberry (49%), rockrose (22%), black locust (14%).

Hive 2 (73 specimens): Tulip poplar (75%), blackberry (8.2%), black locust (4.1%).

Although it is rare (0.26%), honey bees do collect pollen from conifer trees. The degree of conifer tree blooming varies considerably year to year. 2022 was a good year for winter - spring blooming conifers.  

Also in rare occasions (0.13%), 'pollen chunks' found in my hives appear to come from fungi, although the specific fungus species hasn't been identified.  It is known that honey bees collect rust fungus spores instead of flower pollen during the summer dearth.

In spring 2019, I open-fed my bees with Bee-Pro (pollen substitute). Many tan-colored 'pollen chunks' found in my hives looked like below.

Occasionally, I find sugar crystals in pollen chunks. They probably cristalized in nectar.

The smallest pollen I have ever seen was from the forget-me-not, and the largest was from the dwarf iris. Pollen collected from flower stamens are shown.

Sample preparation and mounting methods greatly affect how pollen grains appear under the microscope. As summarized on the Pollen Microscopy home page, I use glycerin mounting (with immediate photography) in most cases. I also use corn syrup mounting to approximate the pollen shape found in honey. The pairs of photos below show how the same pollen sample appears under different mounting methods, with glycerin mounting included for comparison. All photos were taken immediately after mounting.

Pollen collected from tubes sealed on 4/18, 4/22, and 5/1 (first three photos) resembles pollen collected from the stamens of bigleaf maple (next two photos, with the last showing somewhat wet pollen). These grains likely originated from the large bigleaf maple tree across the street.

Pollen collected from a tube sealed on 5/24 resembles that of camas lily and chive, both of which were in bloom in my yard in May.

Pollen collected from a tube sealed on 6/9 was likely gathered by a horn-faced bee, as orchard bees were no longer observed in June. The sample appears to be a mixture of at least two species of different sizes, with the most likely sources being dewberry, columbine, and white sedum.