Sunday, June 01, 2008

Oak Timberworm (Arrhenodes minutus)

Oak Timberworm (Arrhenodes minutus) - Male

Oak Timberworms are sexual dimorphic (i.e. males and females do not look the alike). Males have broad and flat, pincer-like mouthparts while females have long slender snouts. Females use their snouts to chew tiny holes in various hardwoods. They oviposit one egg in each hole, then usually seal the hole with a sticky secretion and frass. Oak Timberworms -- which are actually beetles -- are attracted to wounds on living trees and oviposit only on exposed sapwood. Both sexes feed on sap at wound sites.

(Note: Jim McClarin has an excellent series of photos showing a female boring a hole and ovipositing posted on BugGuide.)

Egg incubation requires anywhere from a few days to three weeks, depending upon temperatures. Newly hatched larvae bore directly into the wood. That's when the real damage to the timber begins. Typically, tunnels are bored nearly straight across the wood grain with little up or down slope. Tunnels go almost to the opposite side of the tree, make a sharp U-turn, and go back across the wood grain toward the entrances. Larvae keep the tunnels clean by pushing the frass outside. Pupation occurs near the tunnel exit from which the adults emerge. The life cycle is generally 3 years, but some individuals develop in 2 years and a few require 4 years.

Known hosts trees include oak, elm, popular and beech. Many other hardwoods including boxelder, honeylocust and aspen are suspected of being susceptible to infestation. These beetles also serve as vectors for oak wilt fungus. They range throughout most of eastern North America from Canada to the Gulf of Mexico.



Anonymous said...

Maybe this is what happened to my oak tree. About half the leaves are burned brown or curled and never opened fully. The rest are OK. I thought it was the drought last year that damaged the buds then set on the trees but am not sure of it.

Anonymous said...

Marvin, it might be interesting to note that these beetles are primitive relatives of weevils, which have taken the narrow, elongated snout idea to an bizzare diversity of uses. Ted

Lana Gramlich said...

Thanks for the info, both Marvin & Ted. I still wouldn't want one on my face. *L*

Marvin said...

Abe: Sorry about your oak tree. This is just speculation on my part, but even if Oak Timberworms are in the tree, I doubt they're responsible for it's decline. As I understand it, they just cause a decline in the value of the timber by filling it with holes. Also, one of the articles I read said they often attack trees that are already stressed and/or in decline.

Ted: Thanks for the additional info. From a human perspective, some weevils have evolved elaborate snouts, but I reckon those snouts serve them well.

Lana: Surely you're not hard-headed enough to attract timberworms -- but only Charles knows for sure. :-)))

swamp4me said...

I just photographed a female oak timberworm this morning. If the pictures are half-way decent I'll post one.

Anonymous said...

Wow, that's an awesome-looking beetle.