Several parkway Norway maples were removed before the holidays and I was able to capture some of the trunk and branch sections. During break I sawed them into sections for use as firewood for the fire pit and wood burning oven. Some branch sections were rotted and dead. And as I cut through these large larvae kept falling out into the snow. And the wood itself was ravaged with bore holes and stuffed with frass. I was getting nervous to think that the larvae might be Asian Long Horned Beetle, the species that devastated the maple tree population 10 years ago. Were they back?! I called up the City Forestry Dept and talked to Joe McCarthy. also know as "Beetle Joe" (he was in charge of the response to the beetles). He asked me to send photos of the larva and the bore holes. I sent him the photos below, and Joe got back to me a bit later.
Identifying larvae is not my forte, but the photo showing wings of an adult deep in the wood would suggest a wood wasp most likely a Pigeon Horntail. Here's more information.
- The pigeon tremex is a type of non-stinging wasp, known as a horntail.
- The giant ichneumon wasp is the most common natural enemy of the pigeon tremex.
- Pigeon tremex are not considered serious pests since attacks are limited to trees and limbs that are in serious decline or very recently dead.
macrurus). The pigeon tremex develops as a wood borer and the larvae are cylindrical-bodied, cream colored grubs that live within the wood. However, they are not considered serious pests since attacks are limited to trees or individual limbs that are in serious decline or very recently dead.
Only certain hardwood trees are attacked by pigeon tremex, notably silver maple, ash, cottonwood, and elm. (Several other species of horntails also occur in the state but these are limited to conifers, usually those growing in forested areas.) However, the insect may become locally abundant as these host trees become increasingly susceptible due to old age or disease. Because pigeon tremex is not considered to be a primary pest, controls have not been developed, although it likely can be temporarily managed by use of insecticides in a manner similar to that of other wood borers. (See Colorado State University Extension fact sheet 5.530, Shade Tree Borers.)
Joseph J. McCarthy
Senior City Forester
Department of Streets and Sanitation
Bureau of Forestry
Awesome wasps in our neighborhood. And think how different a lifestyle between the Pigeon tremex horntail (Tremex columba) (whose larva eat rotten wood) and the giant ichneuman wasp Megarhyssa macrurus (whose larve eat Pigeon tremex horntail larvae)! I recall 4 to 5 years ago we had some cottonwood stumps at school, full of bore holes. And for some days the giant ichneuman wasps would come and rear up its abdomin, insert its very long (2-3 inch) ovipositor into one of the bore holes, and search for a larva to puncture and insert its eggs. The things that go on everyday!
Neither of these wasps sting!