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Sunday, August 28, 2011

The Carpenter Bee and the Tiger Bee Fly

The eastern carpenter bee is about an inch long, with a shiny black hairless abdomen that distinguishes it from bumblebees. 

It's no coincidence that I find carpenter bees and tiger bee flies in the local park. 

Carpenter bees are solitary bees, which means that they don't live in hives like the social honeybees that we normally picture when we think of bees. They are called carpenter bees because they make tunnels in wood. Typically, a female carpenter bee uses her strong jaws to evacuate a tunnel in weathered unpainted wood. She makes a round hole about one-half inch in diameter, and digs in as deep as ten inches. Then she goes to forage for pollen and nectar. When she returns, she shapes pollen into balls that we call beebread. She places a ball of beebread at the end of the tunnel and lays a single egg on it, and then she seals it off with a wall of chewed wood pulp. She provisions six to ten chambers in a row, each with a single egg and a ball of food. When the eggs hatch into larvae, they eat beebread until they become pupae. 

A carpenter bee near the entrance to a tunnel nest. 


New adults emerge at the end of summer, chewing through the soft chamber walls. They do not mate just then; they feed on pollen and nectar and return to spend a quiet winter in the tunnels. The next spring they come out to mate, and the cycle begins again. There is usually just one generation a year, except in warm southern places. They may make nests in human structures -- sheds, porches, roof overhangs, even outdoor furniture -- but they rarely cause anything more than cosmetic damage except when their nests are expanded extensively through repeated use. 

I often see carpenter bees foraging in the flowers at Brooklyn Bridge Park by the East River in New York City. But what's with this tiger bee fly?

The tiger bee fly, Xenox tigrinus, seems to have more than its share of names. Tiger is for the patterned wings. Fly  because it's a fly. Bee because it preys on bees. 


Tiger bee flies hunt for carpenter bees! When a female tiger bee fly locates a carpenter bee nest she may lay eggs at the entrance. The eggs hatch into larvae that find the carpenter bees within. Tiger bee fly larvae usually wait until their prey is in the helpless pupal state, and then they eat it. Notice that the tiger bee fly in the picture is visiting the kind of untreated unpainted wooden post that carpenter bees like to tunnel in. 

It reminds me of this nursery rhyme: 

Big fleas have little fleas, 
Upon their backs to bite 'em,
And little fleas have lesser fleas, 
And so, ad infinitum.

And the great fleas, themselves, in turn
Have greater fleas to go on;
While these again have greater still,
And greater still, and so on. 

See the light colored patch on this carpenter bee's face? That's how you can tell it's a male -- females don't have that mark. 


27 comments:

  1. Well, this is really interesting. because i see both the tiger bee fly and the carpenter in my backyard going in and out of my wood ALL the time. So that's what they are doing in there. The carpenter bee's are pretty big, but they don't bother me. it's the tiger bee fly's that really creep me out!

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  2. I agree that the tiger bee flies are a little scary looking. Lucky you to have something so interesting going on in your back yard!

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  3. I have this too! Right outside my window. So exciting! I have been watching my drone carpenters buzz around all summer, but ever since about mid May these flies came out and I guess ate the bees!

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    1. Good for you! It's cool to know what's going on out there! Julie

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  4. Yea I guess I am lucky too. I have the giant Cicadas and the killer wasps that prey on them as well as Carpenter bees and these Tiger Bee flies all over the place. Regular insects were bad enough with flies and honeybees, wasps and mosquitoes. I am allergic to all sorts of stinging insects, it really rattled my nerves with the addition of the tiger fly now I know better.

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    1. Sometimes it makes me nervous to see the large bees and wasps up close, even the non-aggressive ones. It must be very scary for you to have a carpenter bee fly up close to you like the males sometimes do. Luckily it is all show with them since they are males and cannot sting and the females are very docile. Tiger bee flies are not interested in us at all. Still, it is a good idea to watch any of them from a safe distance and not try to touch them.

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  5. i have carpenter bees, and last year the tiger bee showed up, i killed it, but alas too late. now my bees are being eaten. i got one fly yesterday and just saw another. they are in my porch and i protect my polinators. i only get 2 or 3 bees a year so i fly could kill the whole set up.

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  6. We just had a tiger bee fly show up in my work here in Toronto. I know we have carpenter bees in the neighbourhood but this is the first time I've seen one of these flies. They definitely are kind of scary looking, especially when I picked it up off the floor thinking it was a bit of fabric or thread and it moved. It's quite beautiful once you get over the shock

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  7. Thanks for this post. It helped me identify a tiger bee fly I saw in Boston.

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    1. You are welcome. It's just one of those remarkable looking insects that makes you want to know what it is, isn't it?

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  8. I've had carpenter bees in my deck for years. I generally leave them alone because i find them amusing to watch, however i do know they are really bad for the deck. On occasion the exterminator will spray when he see the holes but it has yet to deter them. This year I have the tiger fly buzzing around the holes... and I'm glad to see her. Talk about organic extermination. Gotta love Mother Nature.

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  9. Thanks to your blog, I now know what a Tiger Bee Fly looks like!

    JennyW

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    1. Jenny, You are welcome. Pretty spiffy looking fly, isn't it? Best, Julie

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  10. Thank you for the info! My dogs were fighting over (playing with) a tiger bee fly (deceased) this morning, I had no idea what it was. We have a variety of bees in the yard, this was by the Rose of Sharon, but I think now I'll take a better look at the deck! It was mostly intact, hoping I don't have to worry about toxicity from partial ingestion - any thoughts?

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    1. Hi, You are welcome. I would not worry if my dog ate a whole one. Best, J

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  11. How sad! I was marveling at the exotic-looking tiger bee fly yesterday in Toronto, in the vicinity of my pollen-bee nest. Now I learn the beauty is a beast!

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    1. Not so sad. Not a beast. Just doing what it does.

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  12. Thank for the info. I always thought they were some sort of horsefly. Now I know why the carpenter bees disappear in July. But do they bite? To bad they don't go after Yellowjackets! Any suggestions on getting rid of them? They're hanging around my hummingbird feeders for the nectar.
    Thanks, Kat

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    1. They do not bite or sting. I would not begrudge them a little sugar water in return for keeping the carpenter bees in check.

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    2. It's good to know they don't bite, thanks. They are not going for the humming bird feeders, it's the Yellowjackets. I wish the fly would get rid of them too! We actually have quite a few of the flies that hang around. Thanks again - Kat

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  13. Thank you for this interesting article. My child and I found this grand creature on our front door this morning, come to pay a polite visit, it would seem. We noticed our usual population of carpenter bees appear to be missing this year... at first I thought it was because we ran out of wood decking for them to chew on. *sigh* Heh. We live in a large acreage of woods, so I don't think we should have to sacrifice the wood deck to the carpenter bees, and we're happy to see Mother Nature has a critter that keeps them in check. ¡Viva la Xenox tigrinus!

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    1. Lucky for you and your child to see one. They are quite striking looking. Nature does have her ways, yes. :-)

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  14. Good article, thanks. They are quite alarming to see at first. They are hard to photograph. They only stick around for a few moments. I leave many dead trees for the wildlife. The ash borers left quite a mess here. I enjoy birding, but there are so many more species of insects to see.

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    1. Hi and thanks. Yep, they are a little scary looking and you need luck to find one sitting still long enough to photograph. :-) Julie

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  15. As I am now reading this on the front porch, the tiger bee fly I had just identified buzzed by and curiously landed on my fingers!

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