I finally got over to my other office and retrieved a favorite reference book. As per weight of bees, Roger Morris and Ted Hooper state that since the early part of the 20th century, researchers have estimated that about 5000 workers make up a pound (11,000 per kg), for an average weight of 90 mg per worker bee. Extreme values in the literature ranged from 5,600 workers per pound (12,500 per kg) to 3000 workers per pound (6,662 per kg).
The most widely accepted figures were those of Mitchell, based on the most thorough methodology. She found 4,451 newly emerged workers per pound (9,804 per kg), 5,159 mature workers per pound (11,360), 3,492 heavily smoked workers per pound (7,690 per kg), and 2,000 drones per pound (4,400 kg). Her work was conducted at UC Davis, 1970,
'Weights of workers and drones in Am Bee Jour 110'.
I've weighed lots of bees, and have found that freshly sampled, live bees usually weigh btw 90 and 100mg. When thoroughly dried, I usually see about 28-30 mg per bee. When sampling live forager bees from hive entrances, I expect btw 4500-5000 bees per pound.
Keep the difference in weight for a fresh/live bee and a dried bee in mind when attempting to compare pesticide residue levels measured in dead and dying bees to Lethal Dose values. 1) Labs like Gastonia often do not quantify the moisture content of samples received for analysis. The sample could be wet from rain, reasonably fresh, or more likely, partially deteriorated and dried from laying on the bottom board or ground for some days before being discovered by the beekeeper. So, the per bee weight could range from about 0.1 gm to 0.3 gm or less as their tissues begin to break down.
One should always count the number of bees in a sample before submitting it for pesticide analysis, along with instructions to the lab to prep the entire sample for analysis, or 2) dry (e.g., freeze dry) the bee samples until they reach a constant weight, then send the sample to the analytical lab keeping a record of the dry weight, and again ask for analysis of entire sample, or 3) determine an estimate of water content before submitting, or 4) ask the lab to dry the sample to constant weight before analysis (that tends to add a lot of lab cost for the extra prep. For our EPA Superfund work, we always dried to constant weight, then kept samples in dessicators until analysis. In a humid climate, a dry bee samples will start picking up weight as soon as the container is opened.
J.J. Bromenshenk
Bee Alert
Missoula, Mt
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