Crawlies with Cri: flower longhorn beetle

Xestoleptura crassicornis flower longhorn beetle
(Photo by Christy Solo, Illinois Valley News)

Don’t let this week’s crawly fool you; even though they very much want you to believe they are a wasp, they are not. Meet the Xestoleptura crassicornis flower longhorn beetle.
That’s a very long name for a beetle who is only one-half inch in length (not counting those fabulous antennae).
Crassis (as we’ll call them) are enigmatic beetles with few recorded specimens. To put a number on “few”, crassi have a nearly identical first cousin – Xestoleptura crassipes. There are 203 sightings of them in Oregon on iNaturalist, and only 29 sightings of crassi(cornis).
There are six species in their Genus (Xestoleptura) all sporting the same overall “I’m a wasp!” look as crassi. Moreover, the patterns on crassis’ elytra (hardened wing covers) can vary quite a bit.
At a glance you might wonder how anyone can sort out which beetle is which to put numbers to those sightings. Our crassi has a Pop! of Color which makes them stand out in their genus crowd. Crassi is the only member with those orangey-orange antennae. Their other wasp-mimicking cousins sport black antennae, sometimes with a bit of brown.
According to Phil Schapker, M.S. in The Longhorn Beetles of the Pacific Northwest, crassis are “relatively scarce” in the Oregon State Arthropod Collection. So, it stands to reason we don’t know nearly as much about crassis as we’d like.
We do know enough to make us like them a lot though. Crassis and other flower longhorn beetles (Subfamily Lepturinae) come by that name honestly. They love flowers and dine on nectar and pollen.
Pop Quiz! Because they fly from flower-to-flower snacking on pollen, that makes them a _ insect? Can you fill in the blank?
If you answered “beneficial” give yourself a gold star! Crassi pollinate those posies as they go. They favor a few species of flowers: thistles, chinquapin and evening primrose. Two out of three of those families of flowers grew in the yard where our pictured crassi was hanging out.
But wait, there’s more to the adult crassis’ diet than nectar and pollen; they’ve also been recorded sipping poison. Just in case their “I’m a wasp!” mimicry fails to deter possible predators, they back up the visual warning by being a potentially deadly snack.
In California, crassi were observed drinking from a wound on a green stem of a blue elderberry (Sambucus nigra cerulea). Elderberry trees contain cyanogenic glucocides. These are highly toxic for animals or micro-organisms due to its inhibition of enzymes of the respiratory chain. An amount as small as 0.5 mg can be lethal to a large mammal.
Birds, lizards, etc. quickly learn which buggy snack will be their last meal and avoid them.
Crassis’ larvae prefer a different fare – dead wood. Specifically dead pine – ponderosa is a favorite, and dead fir. Female crassis have tough, pointy ovipositors they use to drill into dead trees and lay their eggs.
The only possible problem this larval diet could cause is damage to pre-sale, post wildfire-damaged salvage lumber. However, a 2001 Forest Service survey of fungi and wood-boring beetles in newly fire-damaged ponderosa pine found only one, single crassis. They remain enigmatic even at a wood-borer buffet.