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Zombie Bees – Should Beekeepers Worry?

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 -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 Zombie Bees?

Dead honey bee with zombie headstone image.

Are Your Honey Bees – Zombie Bees?

Every time we think we have a “pretty good bead” on beekeeping, something else comes along. Isn’t that the way things go? In the last few years, beekeepers began to notice some very “un-bee-like” behavior in some of their colonies.

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Strange Behavior in Bee Colonies

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 out in cold temps.

Dead honey bees killed by zombie fly image.

Honey Bees Don’t Normally Fly at Night

Honey bees are attracted to light. But, it is unusual for bees to fly at night. Other than some sighting of foraging on full moon nights in warm weather – foragers stay home during the dark hours.

Because, bees use UV and polarized light to navigate and are “blind” without the sun.

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.)

Zombie Bees 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.

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 “Zombie Bees” originated.

Parasitic Fly – Apocephalus borealis

Now, before you go running to grab a silver bullet, wooden cross or garlic necklace, let me explain. 

Zombie bees is the term being used to describe honey bees that are infected by a parasitic fly-Apocephalus borealis. This fly is a species of North American parasitoid phorid fly.  It is smaller than a fruit fly.

Apocephalus borealis, is not a newcomer to the United States, this fly is native to most of North America. Previously known to prey on bumble bees, honey bees have not been a known host.

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.

How Zombie Flies Kill Honey Bees

Zombie Parasitic Fly Life Cycle

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

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 on the inside of the bee over a period of about 7 days. Organs and tissues of the honey bee are consumed by the developing fly larva. The health of the infected honey 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 dont know why.)

The bee will hover around the light until she dies. 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, a new adult fly emerges to begin the cycle anew.

Apocephalus borealis larva exiting bee body image.
Larvae of Apocephalus borealis exiting a honey bee worker (the larvae are arrowed). Photo by John Hafernik Creative Commons Attribution 2.5 via Wikimedia Commons.

How Can Beekeepers Protect Colonies?

There is nothing the beekeeper can do to protect honey bees from parasitic flies. Not every bee in the colony will become one of the Zombie bees.

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.

How Do You Know If You Have Zombie Bees?

Do you see honey bees flying around lights at night? Or trying to get in the windows of your home when the lights are on inside?

Light Trap Tips for Zombie Bees

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

Can Zombie 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 beehive.

Beekeeping Impact of Zombie Bees

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.  Its just another fascinating beekeeping question left to ponder.

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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