Subject:  Some kind of borer beetle?
Geographic location of the bug:  Napa Valley, California
Date: 04/29/2019
Time: 06:04 PM EDT
Your letter to the bugman —
Hello! This morning I saw this beetle sipping from a tree. It’s the biggest one I’ve ever seen outside of a zoo, probably about half the size of my index finger. And looks to be pregnant too! Any idea what it could be?
How you want your letter signed:  Christine

Longhorn:  Stenocorus species

Dear Christine,
This is very exciting.
We agree that this appears to be a Longhorned Borer Beetle in the family Cerambycidae, and the size you indicated is quite impressive.  We did not recognize this Beetle, and the width of the abdomen at the base of the elytra is considerably wider than the thorax, and the thorax is unusual in its shape.  On a lark, we decided to search Cerambycidae and Napa Valley and we found
Vandykea tuberculata pictured on the Cerambycidae Catalog Search, and it does seem to resemble your individual.  We found a single posting on BugGuide and the common name Serpentine Cypress Long-Horned Beetle and the remark:  “on California’s “Special Animals” List.”  We believe this might be a very rare sighting, and we are seeking assistance from Eric Eaton and Doug Yanega to get their opinions.  We will get back to you on this.  We also have selected this posting to be the Bug of the Month for May 2019, and we really hope our initial research has produced a correct identification so we can research this species more.  If that is a correct identification, according to Nature Serve Explorer:  “Critically Imperiled” and “An extremely rare endemic restricted to serpentine cypresses in the Clear Lake area in Lake County, CA.

Longhorn:  Stenocorus species

Correction Courtesy of Doug Yanega
Hi. This is a large female Stenocorus, either vestitus or nubifer. They
are difficult to distinguish based on photos.
Doug Yanega      Dept. of Entomology       Entomology Research Museum
Univ. of California, Riverside, CA

Ed. Note:  Of the two species, BugGuide has information on Stenocorus vestitus which states:  “hosts: Pinaceae (Pinus, Pseudotsuga, Tsuga); adults on flowers”

Wow, thanks so much! It’s always exciting to see new bugs in the spring and summer.

Tagged with →  
Location: Napa Valley, California

2 Responses to Bug of the Month May 2019: Longhorn: Stenocorus species

    • bugman says:

      Thanks Cesar. Doug Yanega wrote back to us: “This is a large female Stenocorus, either vestitus or nubifer. “

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