Zombie Bees

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As if beekeepers don’t have enough to worry about, new challenges are always coming along. Some strange behavior patterns in honey bees -especially on the West Coast of the US (2008) led researchers to look for a cause. Their discovery was a small parasitic fly known to parasitize other insects. How can this small fly turn your sweet honey bees into Zombee Bees?

Dead honey bees zombees image.

What are Zombee Bees?

Every time we think we have a “pretty good bead” on beekeeping, something else comes along. Isn’t that the way things go? It does seem that we are constantly hearing about some new pest or disease that threatens our hives.

So, when we see very “un-bee-like” behavior in our colonies, one of our first thoughts is – now what?

This is the reaction of beekeepers when a strange behavior was discussed that involved zombie behavior in honey bees. No – it is not a joke.

Zombee bees is the term being used to describe honey bees that are infected by a parasitic fly-Apocephalus borealis. This infection is causing some really unusual bee activity.

Dead honey bee with zombie headstone image.

Symptoms of Infected Bees

The problem was first noted in California around 2008. A bug loving biologist, John Hufernik, became aware of strange honey bee behavior.

He was finding dozens of dead honey bees near outside lights each morning. Seeing some bees below an outside light is no surprise but the number of dead were concerning.

Even more puzzling, this was happening even on cool frosty mornings. And, we know that honey bees are insects – being cold blooded they are not normally out in cold temps.

Honey Bees Don’t Normally Fly at Night

Honey bees travel towards light – it attracts them. But, it is unusual for bees to fly at night. Other than some sightings of foraging on full moon nights in warm weather -most foragers stay home during the dark hours.

Because bees use UV and polarized light to navigate, their tracking systems do not function well in the dark.

Of course, bees will leave the hive if disturbed by a predator after dark. This is why you don’t want to be the one holding the flashlight when moving bee hives at night! (They are not attracted to red light though so that is a good substitute.)

Leave the Hive Never to Return

West Coast researchers and beekeepers noticed honey bees leaving the hive to gather at nearby lights. Not the total population of the colony, but many individuals would leave.

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After flying to a visible light source (even if it was not in the close to the hive), the bees would buzz around the light until they died.

There were reports of disoriented dying bees crawling on the ground under the light at dawn. Somewhat like a “zombie that staggers around after dark – never to return to their home”. This is where the term “Zombee Bees” originated.

Infected bees may show disorientation, walk in circles or have the inability to stand.

Graphic listing the possible symptoms of honey bees infected by Apocephalus borealis.

What is Apocephalus borealis?

Does this mean you will see thousands of freaked out bees flying around at night? Before you go running to grab a silver bullet, wooden cross or garlic necklace, let me explain a bit more. 

Apocephalus borealis is a parasitic fly and it is not a newcomer to the United States. In fact, it is native to most of North America.

Smaller than a fruit fly, it was previously known to prey on bumble bees. Honey bees have not been a known host in the past.

Now, we know they are infecting honey bees. Has this been going on for a long time or is it a new development? We do not know.

Parasitic Fly Life Cycle

The cycle begins when an adult female fly lands on the back of an adult honey bee. She sticks her ovipositor (egg-tube) into the abdomen of the bee. Eggs are deposited inside the body of the bee where they hatch into larvae.

Honey bees with parasitic zombie fly image.
Female Apocephalus borealis ovipositing into the abdomen of a worker honey bee. Photo – John Harernik via Creative Commons 2.5

Fly larva feed over a period of about 7 days. Organs and tissues of the honey bee are consumed by the developing fly larva. Naturally, the health of the infected bee continues to deteriorate.

In the later stages of infection, the host honey bee becomes increasingly agitated. She is also attracted to light at night and will fly from the hive. (We don’t know why.)

The bee will hover around the light until she dies. Therefore, you may find a file of dead bees at the base of a lamp post.

When the fly larvae have completed their growth cycle, they will leave the bee’s body and pupate elsewhere for about 28 days. Up to 15 fly larvae may emerge from a single honey bee!

Then, the new adult flies begin the cycle anew.

How Can Beekeepers Protect Colonies

Unlike our techniques for varroa mite treatment, there is nothing the beekeeper can do to protect honey bees from parasitic flies.

Thankfully, not every bee in the colony will become one of the Zombee bees. This gives us hope that a strong colony will not fail due to infestation.

At this time, researchers do not know what role zombie flies play in colony failure. But you can help with the research endeavors by monitoring conditions in your hives.

A citizen scientist project at zombeewatch.org is tracking the spread of Zombees. Their website will give you detail instructions on how to get involved. Also, they have information on how to construct light traps and collect specimens.

Can Zombee Bees Infect Humans?

No, the parasitic fly does not prey on humans. It will only lay eggs on or inside insects. Currently, it is believed that the bees become infected while away from the hive.

Method of Testing

Do you see honey bees flying around lights at night? You may notice unusual activity of them at windows of your home when the lights are on inside. In areas with known problems, light traps many be used.

Following the website directions (zombeewatch.org), construct a light trap. These are simple to make with such items as a plastic jug and safety light using a compact fluorescent bulb.

Don’t place the light trap close to your hives – they should be well away. You do not want the light to shine on the entrance of the hives. You may encourage bees that are NOT Zombees to come out.

Any bees that you catch should be collected with tweezers or forceps – don’t touch them. Be careful dying bees can still sting. Transfer the dead bees into a sealed container and place away from the sun.

Check periodically for small brown pill shaped pupae inside the bottle or jug. They look like small pieces of brown rice to me. The pupae should appear between 5-14 days after collection. In another 15-28 days you may see flies.

Report your data to the watch program. It is important to their research to learn your results whether positive or negative.

Conclusion

Will this honey bee pest become a major killer of honey bee colonies? Will it be another “mite-type” issue that beekeepers must struggle to control?

We don’t know how big an effect this parasitism has on a bee colony. But of course, it is not a good thing.

Beekeepers need to be aware of the problem but not overly dramatic. Researchers continue to study the problem and you can help.

There are many parts of the United States still in need of monitoring. This is a great opportunity to help the beekeeping community. And it is open to beekeepers and non-beekeepers.

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