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Knapweed Root Weevil (Cyphocleonus achates)

Detailing the physical features, habits, territorial reach and other identifying qualities of the Knapweed Root Weevil

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Image Credit: Tom H. from WA
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Image Credit: Tom H. from WA
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Image Credit: Tom H. from WA
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Brought to the continent to battle knapweed, this light-colored weevil helps control the growth of the aggressive weed.

Updated: 02/14/2023; Authored By ; Content ©www.InsectIdentification.org
Spotted Knapweed is a Eurasian plant that was first seen in North America in the late 1800s. It is highly invasive thanks to a chemical in its roots that prevents other plants from growing near it. Native plants cannot compete with it, so a patch of Spotted Knapweed can eventually become a field. Enter the Knapweed Root Weevil! This beetle is a natural predator of the plant, and its larvae feast on the roots from winter to summer. Their feeding behavior hampers the host plant's health, weakening it or killing it. Though it takes a few summers, with a large enough population of Knapweed Root Weevils, the spread of the weed diminishes and native grasses and flowers can return. This is an excellent example of an effective biological control since this species only eats Knapweed. In areas with chronic Knapweed growth, local Extension offices should be able to help landowners find a good source for purchasing these weevils and recommend the best time to disperse them in that area.

Spotted Knapweed grows in central and western prairies in Canada and the northern U.S. The weevil's range coincides with this. It is a mottled white and light brown color with small black specks all over their body. A black midline runs the length of its 'nose'. Legs are also light-colored, and it may be difficult to find despite its large size (for a weevil). It does not bite or sting. If you see one on a plant, leave it be. It is doing a great service to the ecosystem.©InsectIdentification.org

Known Diet of the Knapweed-Root-Weevil-Beetle

knapweed roots
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General Characteristics

Capability, Shape, Texture/Pattern, Benefits, Dangers
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Taxonomic Hierarchy

Species Breakdown
Kingdom: Animalia
  Phylum: Arthropoda
    Class: Insecta
      Order: Coleoptera
        Family: Curculionidae
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          Genus: Cyphocleonus
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            Species: achates

Identifying Information

Size, Colors, Features
Scientific Name: Cyphocleonus achates
Other Name(s): Root Boring Weevil
Category: Beetle
Size (Adult; Length): 15mm to 18mm (0.59" to 0.70")
Colorwheel Graphic Colors: white; brown; yellow
Descriptors: tiny black dots; mottled color; pale; light-colored; long nose; snout; bent antennae; white legs; tubular

Relative Size Comparison

Typical Size Between 15mm (0.6in) and 18mm (0.7in)
Lo: 15mm
Md: 16.5mm
Hi: 18mm

Territorial Map*

U.S., Canada, and Mexico
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Prince Edward Is.  
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Knapweed Root Weevil may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Knapweed Root Weevil. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.
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