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Assessing a pile of dead bees: what happened?

After mosquito spraying in his neighborhood, Jim Metrailer of Little Rock, Arkansas, discovered a pile of dead bees. He wondered if his bees got into the spray itself or if they ate poisoned nectar. He also wondered if his bees had succumbed for another reason entirely.

Many choices

The answer to the first question is complex. Hundreds of different insecticides are available, but those for mosquito spraying are somewhat limited in popularity. From what I’ve read, many of the commonly used ones are broken down by sunlight, quickly becoming harmless once they are exposed to bright sun.

It’s been many years since I studied pesticides as an agronomy student, and the formulations have all been replaced or enhanced. I simply don’t know the specifics and I don’t want to spend the time to re-learn them. If you want to know the details, you need to find the name of the chemicals used in your area and look them up.

Systemics vs contact poisons

Poisoned nectar usually isn’t a problem unless a systemic pesticide was used. A systemic moves to all parts of a plant through the vascular system, reaching the leaves, stems, roots, fruits, nectar, and even the pollen. This is why seeds coated with the neonicotinoids are such a problem for bees.

Generally, it works like this: First the seed is factory-coated with the chemical. After planting, the pesticide coating washes into the soil. When the roots start to grow, they pick up the chemical along with water and nutrients, then transport it through the interior of the plant. No matter which part a bug eats, it gets a dose of poison.

Since mosquitoes don’t eat plants, exterminators use contact poisons on them—something that is absorbed through the exoskeleton when it lands on the insect. You see contact poisons in things like household bug sprays that kill almost instantly. Often they affect the central nervous system of the victim.

Jim’s bees

Depending on when the spray was applied and what kind was used, Jim’s bees could have been exposed in several different ways. If the pesticide was applied during flying times, they could have been sprayed directly. If the bees traveled to a plant soon after application, they could have come into contact with it on leaves or petals before it broke down. Or, if a systemic was used on certain nectar plants, the bees could have collected poisoned nectar that had nothing to do with mosquito spraying.

Only one of Jim’s two colonies was affected, so they were probably foraging in different areas. One got into it and one didn’t, which is not unusual.

Altruistic bees can accumulate

Without further investigation or testing, it is difficult to say exactly why a pile of dead bees accumulated. Honey bees exhibit altruistic behavior, meaning a sick or dying bee will often fly out of the hive and die in order to protect the rest of the colony from the same fate. They may leave the hive and fall immediately to the ground or sickened bees may be carried out by others. In either case, quite a pile can build up.

Besides insecticides, bees may pile up from a number of different brood diseases, nosema disease, and even viral diseases carried by varroa. However, the rate of accumulation can tell you a lot.

My own pile of dead bees

Last year, I had two colonies succumb to pesticide on a spring day. The reason for my certainty is simple. I was getting ready to go on a trip. On the afternoon before I was due to leave, I did thorough hive inspections where I looked at all frames in all hives. I usually check things before I depart because I don’t want to leave my non-beekeeping husband with a bee problem in my absence.

In this case the colonies looked great. They were active, packed with brood, pollen, and making lots of honey. They were not feisty at all, but were as busy as bees. I was relieved to find no problems. The next morning, two colonies were toast, all piled neatly in front of their respective hives.

When I reported this here in a post, a number of people said it maybe wasn’t pesticide but probably a disease. To this I say, no no no. Why? The rate of accumulation was too great.

How fast they pile makes a difference

A colony that was poisoned can die all at once. Most diseases start slowly and build up, so you are likely to get a pile that starts small and then grows. But with poison, a pile can appear within hours. The rate of accumulation is important diagnostic evidence. Even without looking for extended tongues, deformed bees, or signs of disease, the rate gives you a clue.

In my case, I examined every frame and found no sign of anything amiss twelve hours earlier. And since nothing else happened in the interim—no floods, forest fires, suffocation, intense heat or cold—they almost assuredly died of pesticide. Another important clue is simultaneity. How many colonies totally collapse from disease in exactly the same twelve-hour time frame?

Sometimes we don’t know

Of course, if you haven’t paid close attention to your bees, it is harder to say. For example, if I found the piles after I returned a week later, then more investigation would be required. But in this case, I knew they were healthy the evening before, so something big happened during those hours.

Thanks, Jim, for a great question. It is a subject we should think about when assessing any colony problem: look at the evidence carefully before making a diagnosis. Don’t rely on gossip you heard at a bee club. Sometimes the conventional wisdom just doesn’t make sense.

Rusty
Honey Bee Suite

Jim found this pile of dead bees in front of a hive soon after pesticide spraying nearby. Fortunately, this colony recovered from the incident.
Jim found this pile of dead bees in front of a hive soon after pesticide spraying nearby. Fortunately, this colony recovered from the incident. © Jim Metrailer.

Comments

Deb Corcoran
Reply

Good evening Rusty, that photo of dead bees does indeed look like a pesticide kill, as it looks like a “carpet of dead bees” not a pile. I learned this from the U.K. National Honey Show video with Kirsty Stainton lecturing on the foulbroods and CBPV, Chronic Bee Paralysis Virus, which 3 of my hives (out of 17) had last summer/autumn. She shows the difference on the lecture video between the virus pile and a pesticide carpet of dead bees. Thanks again for all the great research you do. Deb

Rusty
Reply

Deb,

Thank you for that insight. I’ve never heard that before but I can picture those two kinds of accumulation in my mind because I’ve seen them both. What a handy tip!

David Smith II
Reply

When we say “fortumately this colony recovered from the incident” I’m glad to hear it, but, it makes me wonder how the pesticide manufacturers react to that. Gives them a green light. They don’t see how that pile of bees could have made a nuc, or bumper crop. They see the word “recovered” and all is well. Just my 2 cents. I had 173 colonies last October, and started this spring with SIX. Ugh. No “proof” it was pesticides, but I’ve been keeping bees for nine years, and never had a loss like this. Thanks for your posts, and letting me vent.

Debbie in Ohio
Reply

Unfortunately this is a sight we see too often. There should be strict laws that spray is applied during evening hours when it’s still dark out and hopefully the stuff will dry before the bees get up. It’s terrible too that the insects that help us with mosquitoes the most also get killed off in the ditches when they spray. And the damage to other wildlife in the area, birds, ditch turtles and toads, little chipmunks. Every time I see a truck go down a road in the middle of the day spraying the ditches I get really angry. I feel like taking the spray wand and spraying the person applying the poisons. ha ha ! We also have to be careful that the poison does not get ‘stored’ in the bee bread, then one ends up with another kill of the brood and the emerging bees. What’s a beekeeper to do? Beekeeping is definitely NOT easy. It appears that just about everything is against the little workers.

Rusty
Reply

Debbie,

You are correct. I come really close to giving up when I see and hear all these things. It seems most people want to kill the planet, and they are doing a good job of it.

Tom Rearick
Reply

I lost three hives to a neighbor’s non-selective spraying a couple years ago. It made me question if I wanted to continue beekeeping. Instead of quitting, I wrote an article for Bee Culture on Zika and Bee Kills (https://www.beeculture.com/zika-bee-kills/). I’ve since realized that to reduce the dependence on non-selective spraying for mosquitoes, home owners need to be aware of alternatives to calling the local mosquito control company. This time, I’ve written a paper, “How to Control Mosquitos Without Killing Honey Bees and Other Beneficial Insects”, and I am distributing it any way I can. You can download the PDF file at http://www.beehacker.com/wp/wp-content/uploads/2019/07/mosquitoControl.pdf. Give a printed copy of it and a bottle of honey to your neighbors.

Rusty
Reply

Thanks, Tom. I printed a copy to read later today. I’m glad to see people taking action instead of giving up. Sometimes it’s hard to go that route.

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