Do My Honey Bees Have Nosema?

Paul Amey for northern Vermont writes:

I was inspecting my hive today for the first time this season and noticed the bees were not very interested in sugar syrup.  It made me wonder if they had Nosema. A friend who knows more bee science than I do mentioned it, but I’ve never had it before and don’t really know what to look for.  There were five frames with 3/4 of bees on them, an active queen, no capped brood, some eggs, and a small amount of very small open brood. Also, a huge amount of dead bees in the bottom, more than usual winter kill, though it was a strong hive last fall. The bees were flying a lot, and were bringing in pollen. There are still piles of snow about, so it’s early in the bee world. The bees in the hive did not act like anything was amiss, and they have a lot of leftover honey, plus a pollen patty on top that they’ve been munching on.

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We reached out to Rusty Burlew for her thoughts on this topic.

Based on your description, I don’t see any reason to suspect Nosema disease. In fact, it sounds like your colony is fine. Nearly six frames of overwintered bees at this time of year in Vermont is excellent. In addition, you say the bees are eating a pollen patty and acting normally, so it’s hard to visualize any disease at all.

You mentioned the bees weren’t interested in sugar syrup. Excellent! Once nectar becomes available, and the daily temperatures are warm enough to forage, your bees will have no interest in bland and tasteless syrup. You want your bees to collect nectar, not syrup, so this is encouraging news.

You also say you’ve seen “a huge amount of dead bees in the bottom, more than usual winter kill.” Winter kill is never usual. The phrase refers to some stochastic (or uncharacteristic) event that kills a colony. This event could be a particularly vicious cold snap, strong winds, or perhaps a storm with large amounts of precipitation—anything that quickly kills a colony. What I believe you are referring to is daily attrition.

Bees die every day, which is why the queen lays hundreds or even thousands of eggs in a day. Spring and summer bees have an average lifespan of four to six weeks, and an average-size colony in good weather loses perhaps 1,000 to 1,200 bees per day. The beekeeper doesn’t see them because they die out in the field. Winter (diutinus) bees live longer—eight months or so. During the winter, a normal colony loses a couple hundred per day. Depending on the amount of no-fly weather, these pile up on the bottom board. By spring, a layer of bees two or three inches thick is not unusual. But to reiterate, that build-up of dead bees in is not “winter kill,” but rather normal attrition.

The accumulation of dead bees may even increase just as the spring bees begin to emerge. This occurs because the remaining long-lived diutinus bees are at the end of their lives, and once the young bees begin to emerge, the old ones are no longer needed and are quickly replaced.