'Milk chocolate crunch weevils' often seen in peninsula houses

Refuge Notebook

Posted: Friday, October 26, 2007

 

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  Shown is weevil damage to mountain ash leaflets. The beetles chew semicircular divots out of leaf edges. The mottling of the leaves is probably due to mountain ash-juniper rust, a fungal disease. Photo by Matt Bowser

The common weevil Trichalophus alternatus is often found indoors in Peninsula houses.

Photos by Matt Bowser

The faint pitter-patter of little brown weevils dropping from walls to the floor and their louder crunch underfoot are familiar sounds in many homes of the western Kenai Peninsula. These hard-shelled, 1/2-inch-long beetles can be abundant in the summer, crawling up walls, entering houses, and often ending up in bathtubs and sinks. As an entomology student serving the Kenai National Wildlife Refuge, I get more questions about these beetles than any other animal. I spoke with Janice Chumley of the University of Alaska Fairbanks Cooperative Extension Service in Soldotna, who also receives numerous inquiries about these weevils. Below I have listed the questions most frequently asked of us regarding these beetles and have provided the best answers that I have.

What are they?

Dr. Charles O'Brien, a world authority on weevils recently retired from Florida A&M University, identified specimens from the Kenai as Trichalophus alternatus. "Crunchy bugs" and "milk chocolate bugs" are names for them I have heard used by area residents, good descriptions of their texture and color, respectively. They have no recognized common name, so perhaps we could propose a name such as the "milk chocolate crunch weevil".

What do they eat?

Our Trichalophus weevils appear to be true generalists, munching on just about any deciduous shrub. On the western Kenai, they eat willow, alder, birch, aspen, dwarf dogwood, prickly rose, highbush cranberry and mountain ash. The adults are most active at night and can be observed feeding with the use of a red-filtered light (most insects do not perceive red light). They feed at the edges of leaves, chewing distinctive, roughly 1/3- to 1/2-inch-wide semicircular divots out of leaf edges. They are harmless to people.

The larvae of Trichalophus alternatus have not been studied, but larvae of this group of weevils generally feed on roots of deciduous shrubs. They are probably generalists as are the adults. I have found beetle grubs among the roots of a cottonwood tree in my yard that were likely the larvae of Trichalophus. I have also found damage to willow roots probably attributable to this species.

While the feeding of the adults may slightly affect the appearance of ornamental shrubs, they seem to have only a minor impact on the health of their host plants. I have not seen instances of severe defoliation due to these beetles even where their abundance was quite high. The ecology of the larvae is unknown, but at least I have not heard of or seen instances of death or decline of host plants attributable to these weevils. I have seen willows with some root damage, but they appeared healthy in other respects.

Why are they in my house?

I do not know why these weevils enter houses. They may be dispersing in search of host plants, seeking out moisture, looking for mates, or trying to find nice places to hide during the daylight hours. Because they have shortened flight wings (hidden under their shield-like first pair of wings), they only travel by foot. This is why they cannot escape from smooth-sided bath tubs and sink basins. Regardless of why Trichalophus weevils enter houses, they fare poorly indoors, usually exhausting themselves and dying in a corner.

My guess as to why they so commonly ascend walls is that this is their natural response to vertical surfaces. In their normal environment, the only vertical surfaces extending from the ground are the trunks and stems of their food plants. Like many arboreal insects, Trichalophus weevils respond to a perceived threat by quickly dropping from foliage to the forest floor where they blend in with leaf litter, an effective strategy in the wild. They behave the same way when disturbed on walls. Once alarmed, these beetles usually "play dead" for some time.

 

Shown is weevil damage to mountain ash leaflets. The beetles chew semicircular divots out of leaf edges. The mottling of the leaves is probably due to mountain ash-juniper rust, a fungal disease.

Photo by Matt Bowser

How can I get rid of them?

Janice Chumley had several recommendations. Gaps, such as spaces around doors, should be sealed. Double-sided sticky tape along thresholds and other points of entry can also be an effective barrier. Once in the home, the beetles may be swept or vacuumed up. Further measures should not be warranted since they are generally no more than a nuisance. They are native beetles, denizens of our natural environment that inadvertently and unfortunately tend to make their way into our man-made environments.

Matt Bowser is a graduate student in entomology at the University of Alaska Fairbanks. He has worked at the Kenai National Wildlife Refuge since 2004, and lives with his family in Soldotna.

Previous Refuge Notebook articles can be viewed on our Web site, http://kenai.fws.gov/. You can check on new bird arrivals or report your bird sighting on the Kenai National Wildlife Refuge Birding Hotline at (907) 262-2300.



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