Wednesday, November 14, 2012

Wasp Wednesday: Blue-winged Wasp

One of the most common solitary wasps of late summer and fall is a member of the family Scoliidae known as the “Blue-winged Wasp,” Scolia dubia. This is a fairly large insect, 20-25 millimeters in length, and easily identified by its bi-colored abdomen: Black on the upper half and red on the bottom half, with two bright yellow spots in the red area. There is rarely any variation in that color scheme, either. The common name stems from the brilliant blue highlights in the black wings that shine when sunlight hits them just right.

Scolia dubia is also a widespread species, found from Massachusetts to Florida, and west to Colorado, Arizona, and southern California. I have found them in New Jersey, Ohio, and Colorado. They are parasites of the grubs of scarab beetles, particularly the Green June Beetle, Cotinis nitida, and Japanese Beetles, Popilla japonica. Since Colorado has neither of these species, the Blue-winged Wasp must exploit a different host here. We certainly have plenty of May beetles (genus Phyllophaga), and the Bumble Flower Beetle (Euphoria inda), so I suspect those are the local hosts here in Colorado Springs.

The female wasp somehow divines the presence of beetle grubs underground while flying low over the surface of the soil in what approximates a figure-eight pattern. When she detects one, she lands, and sets about unearthing it. Scoliid wasps have strong legs that are heavily spined. This adaptation facilitates their digging activities.

An exposed scarab grub will writhe around and seek to rebury itself immediately. The wasp stings the larva to paralyze it and allow her to manipulate it. She may leave the grub in situ, or tunnel below it, excavating a small chamber where she deposits the beetle larva and lays an egg on it, perpendicular its body. She then seals the chamber and leaves to start the process all over again, often staying underground and digging her way to the next grub.

Interestingly, these wasps may sting several grubs without laying eggs on them. The paralysis of the beetle larva is usually permanent, so regardless of whether they become food for larval wasps, the beetle grubs are unable to complete their own life cycle. This is a good thing if you happen to have an infestation of “white grubs” in your lawn or garden.

Back to the egg on the beetle grub, though. The wasp larva that hatches feeds as an external parasite on the grub for one or two weeks before spinning a silken cocoon around itself. There it will remain as a pre-pupa for the winter, pupating the following summer and eventually emerging as an adult wasp.

Male and female scoliid wasps commonly visit flowers to feed on nectar (and perhaps pollen). I find them most often on White Sweet Clover, Melilotus alba, thoroughworts (genus Eupatorium), and goldenrod (Solidago spp.). Males can be identified by their long antennae and overall more slender appearance. Males have a distinctive, three-pronged “pseudostinger” that is part of their external genitalia. Males cannot sting, and females are loathe to sting unless physically molested.

Another interesting aspect of the males is their behavior. Males also fly near the ground in a sinuous pattern, hoping to detect virgin females emerging from the ground. This usually happens in the morning, and males abandon their searching by late afternoon. At that time, they may gather together to roost for the night on vegetation, as the image below depicts.


© Tim Moyer via Bugguide.net

Keep an eye out for the Blue-winged Wasp in your own yard. Remember they are beneficial, but beware that large numbers of them may indicate you have a serious problem with white grubs.

Sources: Grissell, Edward E. 2007. “Scoliid Wasps of Florida, Campsomeris, Scolia, and Trielis spp. (Insecta: Hymenoptera: Scoliidae),” Featured Creatures, document EENY-409, Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences (IFAS), University of Florida.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp (Dover Edition).

27 comments:

  1. Thank you for this very detailed post. We have been looking everywhere trying to identify this wasp. And it just so happens we had a June bug infestation in our Pennsylvania vegetable garden this year. I spread beneficial nematodes and was thrilled to see that these wasps also feed on the grubs.

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    1. Glad I could help! Thank you for the compliments :-)

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  2. Hey, Eric! I haven't seen these particular wasps, but I have a black & yellow variety that seem really interested the large clusters of Bumble Flower-Beetles on my Sunflower stalks. The garden is in Longmont, north of Boulder.

    I deadheaded the Sunflowers (Russian Mammoth)because a couple of them bloomed a second time. I left the stalks because my Morning Glories & Gourds are climbing them. Plus they provided some filtering for the direct sunlight & contribute to the microclimate of the bed.

    Then the Beetles showed up & now there are a lot of Wasps that are always buzzing around the clusters of Beetles. I'm just curious what the relationship is. It took me forever identify the Beetles!

    Thank you for your help!

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    1. Kelley, I'm puzzled by your description, too. Any chance you can take some images and send them to me (bugeric24ATyahooDOTcm)? I'm quite curious.

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  3. Just saw one of these in Davis, California on our mint flowers. Thanks for the info!

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    1. You're most welcome! It may have been a related species that you saw in California, though. Not sure this one has made it that far north, though I could be mistaken.

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  4. Thanx Eric. Appreciate the info. Remarkable that such a "common" insect is virtually unknown by all the so-called pros in my area of no.va. and as for treatment I don't understand how a shrug of the shoulders will solve my problem. ur article is a big help.

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    1. You're welcome; and thank you for the compliment.

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  5. In Greenwich NJ (Cumberland County) there are hundreds of these on my sedums - only in the afternoon.

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  6. We have hundreds (if not more) on our property in nrn MD, obviously a reflection of the massive Japanese Beetle infestation we've had the past two summers. Interestingly, we previously had large numbers of the large Green June Bug; after the scoliid wasps showed up en masse' last summer, we had very few Green June Bug beetles this year. Makes sense, as that grub is big and would be an easy target. Obviously, we've got a grub issue courtesy of the invasive Japanese Beetle (don't wish these on anyone), but I'm not going to poison the yard cos I don't want to kill the beneficial larvae of the wasps as well a other insects. For this, I'm gonna see if Milky Spore will do the trick. Anyhow, good info!

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  7. I love seeing these on my Mountain Mint. I had assumed they were native but have see on one website that they are from Japan. Another website says they are native to here. Other sites just talk about their range in the U.S. So my question is, are they native to the U.S. or to Japan? Thanks.

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    1. This species is native to North America, as far as I know....At least one wasp in the family Tiphiidae has been introduced from Japan in hopes of controlling Japanese Beetle. I think that might be how you are confused.

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  8. I just encountered my 1st blue winged wasp in my yard in East Tennessee. It was dragging a ground spider at least 3 times it's size thru the grass

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    1. That would be a completely different wasp, in a different family (Pompilidae)....but lucky you to witness that!

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    2. I just saw the same!! But it was from my front step. The spider was there. Next thing came the wasp. I guess it killed it and then it dragged the spider off the step, through the mulch and up the side of the house. And the spider was about 4 times its size. I have a lot of it recorded if you'd like to see it. I'm also in NE Tennessee. Kingsport to be exact

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    3. Again, you are both describing Tachypompilus ferrugineus, a large spider wasp that will sting a wolf spider or fishing spider into paralysis and store it as food for her larval offspring. Different family of wasps with different hosts. :-)

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  9. Like most people thanks for the information. I live just outside Nashville and have about 50 of them flying low to the ground but not bothering us or our dog. Have never seen them before. Hope I don't have a grub problem but I guess they will help. Also quite a beautiful creature!

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  10. I've just encountered a large number of these at our home/farm in KY. I feel certain this is what they are. There are what appear to be literally thousands floating around the yard, more so early in the day. Should I treat my yard with something to stop and prevent this? I've got several young children that I've been keeping indoors because I don't want them to get stung - I really hate to confine my kids to the house.

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    1. It is almost certainly the males you are observing, and they do not sting. Also, such phenomena are short-lived and you won't see them in a matter of days. Plus, if they are mostly active early, the kids can play later. I never recommend chemical treatments for *any* insect. Remember these wasps are also doing you a favor by controlling "white grubs" that damage your lawn.

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  11. Hi there, i saw something similar to this today but the bottom red half of the body was smooth not fuzzy, it had a 10mm stinger and white eyes. It did have the trademark red lower body and blue wing colouring but with no yellow spots on the abdomen. Would love to send a pic and wondering what it could be.(Patrizia in S. Ontario)

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  12. Thanks also for the info on the blue winged wasp.I discovered 4 sitting on a reed just before dusk. I was so intrigued I took several photos to show my husband. He had never seen them before. I am so glad they eat scarub grubs! Linda

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  13. Hey Eric,
    We have a good 25-50 buzzing around on the front lawn most sunny days - they do not seem to like cool times of the day. They've been at it for a couple of weeks. No one we know has ever seen them before, but they are definitely Blue-wings.

    Couple of questions - do they live individually in the ground or do they have a nest?

    For how long will they be around?

    Will they return every year? Or just this year until they've killed the white grubs?

    In all honesty, we're not that keen on them altho they are not aggressive. We basically can't play or use the front lawn during the day there's so many. Is it possible to relocate them safely?

    Much thanks in advance, Alex A, Philadelphia PA

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    1. They have probably "moved on" already, but if not then they will shortly. Further, it is likely mostly the non-stinging males you are seeing that are seeking females. In any event they are solitary, and females will not sting unless you grab one or step on one in bare feet.

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  14. PS The only beetles we've noticed - and not many - are Masked Chafers.

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  15. Thank goodness for your pictures of the Blue Winged Wasp! Looked everywhere for what kind of wasp I have flying low to the ground in my yard in SW PA. They didn't seem to be aggressive , but good to know they are beneficial too!

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  16. In Fort Worth, Texas,we've been watching four of them tunnel nests. Two of them brought tiny green grasshoppers (katydids?) into the nests at least once a day for several days! Also, while one mom was deep inside the nest, I accidentally dropped just one drop of water on the perimeter. She seemed quite put out and spent over five minutes repairing the damage. And they are really strong. They can move huge pieces of pine bark mulch up out of a tunnel.

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