Wednesday, February 29, 2012

Wasp Wednesday: Not Wasp VII

Imagine one’s surprise at finding wasps suddenly appearing inside their home in the middle of winter. It is not impossible, as queen yellowjackets and some female paper wasps hibernate, overwintering inside houses and other human structures. They may stir if they find their way inside to heated rooms. However, other kinds of insects can be mistaken for wasps. I recently had occasion to identify one such masquerader.

One of the keepers at the Cheyenne Mountain Zoo here in Colorado Springs discovered wasp-like insects emerging from woody “perching material” used for birds in the African Rift Valley exhibit. To her credit she recognized them for what they really were: beetles.

These insects are black with yellow stripes, superficially resembling the markings of yellowjackets. They also run very rapidly, which enhances their resemblance to stinging insects. Many species of longhorned wood-boring beetles in the family Cerambycidae are convincing wasp mimics, and indeed that is what these specimens turned out to be. It was a bit more challenging to determine exactly which genus and species.

It helps to know what a beetle’s “host plant” is when trying to identify it. This only applies to herbivorous species, of course, but it is surprising how many vegetarian beetles feed on only a handful of different plant species. A variety of dead limbs from native hardwoods and conifers are used by zoo personnel for structural objects in exhibits, or as enrichment items to make life in captivity more humane and enjoyable for the animals. So, I knew the beetles were of local origin rather than something imported accidentally from overseas.

From my experiences in Oregon, I had my suspicions as to what genus this beetle belonged to: Neoclytus. There are 25 species in North America, so the next step was determining which ones are found in Colorado. Using a publication on Colorado Cerambycidae (Heffern, 1998), I learned that there are five, maybe six species of Neoclytus known from the Centennial State.

I was able to go online and look up images of the common Colorado Neoclytus species, and the only one to match the specimens given to me by the zookeeper was the Banded Ash Borer, Neoclytus caprea.

Although ash (Fraxinus spp.) is the favored host, the Banded Ash Borer is known to bore in a variety of dead and dying trees. Netleaf Hackberry (Celtis reticulara), hickory (Carya spp.), elm (Ulmnus spp.), oak (Quercus spp.), mesquite (Prosopis spp.), walnut (Juglans spp.), eucalyptus (Eucalyptus spp.), and grape (Vitis spp.) are all hosts to the wood-boring larval stage of this beetle. Trees weakened by drought, disease, fire, and attacks from other insects are especially vulnerable. Rarely are healthy trees attacked.

Adult beetles normally emerge in early spring. After mating, females lay eggs in bark crevices of the host tree. The larvae that hatch from the eggs tunnel just beneath the bark before boring into the sapwood where they feed for most of the summer. The larvae pupate in autumn and overwinter in that stage.

The adult beetles measure 8-17 millimeters, size being a function of the amount of nutrition received in the larval stage. This is a widespread species, found throughout the U.S. except for the Pacific coast. It also ranges into eastern Canada. Look for adults outdoors from March to June. They emerge on the early end of that spectrum in more southerly latitudes.

Ash logs felled in winter are especially prone to attack by the beetles in the following spring. Infested logs brought indoors for firewood may spawn an early emergence of the beetles due to the artificial warmth and extended “daylight” presented by indoor stimuli.

Milling of infested timber may actually prolong the life cycle of wood-boring beetle larvae that survive the process. Dry wood may offer less nutritional value to the grubs trapped within it, meaning that a normal yearly life cycle may be extended to several years in the case of the Banded Ash Borer.

The next time you find a swarm of “wasps” in your home, check the firewood first, and see if it might not be beetles like the Banded Ash Borer, the Hickory Borer, or a related species. Relax, they are at most a nuisance.

Sources: Heffern, D. J. 1998. “A survey of the Cerambycidae (Coleoptera), or longhorned beetles of Colorado,” Contributions of the C. P. Gillette Museum of Arthropod Diversity. Colorado State University: Department of Bioagricultural Sciences and Pest Management. 32 pp.
Karren, J. B. and Alan H. Roe. 2000. “Banded Ash Borer,” Fact Sheet 11, Utah State University Extension.
Yanega, Douglas. 1996. Field Guide to Northeastern Longhorned Beetles (Coleoptera: Cerambycidae). Champaign, Illinois: Illinois Natural History Survey Manual 6. 174 pp.


  1. Thanks for your informative post! I found the exact same bug in my house two or three times and was fearing an infestation of strange-looking wasps. I live on the Pacific coast and use a wood stove with imported oak, so I'm guessing the bugs were imported too. :/ Do you know if it's bad to burn the wood that is infested or if we need to spray the wood to prevent more larvae from spreading? We just ordered a 1/2 cord of wood and it was expensive and our only heat source, so I'm a little worried that these little critters are destroying our wood supply that's supposed to last us into next winter.

    1. There are actually several different longhorned beetles that resemble this one, so it may not be the same species....Nothing wrong with burning the wood as is, but what disturbs me is that you are IMPORTING it! Do not do that! That is the primary way exotic pests like the Emerald Ash Borer and Asian Longhorn Beetle have spread. Use LOCAL wood, please. Thank you.

  2. Thank you! My daughter is grateful for this info :)

  3. Hi,

    From your description we have found this bug in are home in England!, do you no weather they damage any furniture?

    1. It is likely a different species that you have in the UK, but they do not actively attack furniture. However, if a larva was actively tunneling through milled lumber that *became* furniture, it would complete its development and eventually exit the table or chair or cabinet.

  4. I put up a fireplace mantel and we've found these in the house. I put a light on my mantel and there are new holes coming out of the piece. Do I need to be worried about this? What should I do?

    1. They may cause cosmetic damage, but probably not structural damage. You may wish to consult your local County Extension Service agent, though (Cooperative Extension Service, usually with an office in the city or town that serves as the County Seat).

  5. Thank You for the excellent explanation. After seeing what these buggers could do when I split some infested firewood
    (WOW)(extremely agressive tunnelers...lots of boring dust on the woodpile from just a few infested logs) I was concerned that some may have hitched a ride indoors. Good to know that my home is not on their 2018 menu.