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How to identify it
- Females are elongate, shiny and uniformly brownish copper, about 3/8 inch (10 mm) long. Males are smaller, about 8 mm, with a reddish copper thorax and black wing covers that reflect green, blue and violet.[1][2]
- The eggs are tiny, flat disks 0.8 to 1.1 mm across, glued to twig bark under a clear coating. They look like the covers of small scale insects, turning from pale yellowish green to almost black before they hatch.[1][2]
- The larva is a slender, flat, legless, yellowish white flatheaded borer that grows to about 3/4 inch (15 to 20 mm) long.[1][2]
- The damage is the surest sign: a thin gallery under the bark that suddenly turns and winds in a tight spiral to the center of the stem. NC State calls this spiral tunnel diagnostic for the species.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Twig girdler | The hickory spiral borer's larva cuts the stem from the inside: a winding cut that runs from the inner bark to the heart of the branch and leaves the bark and sometimes a few fibers at the center. The spiral borer severs stems 8 to 40 mm thick, many of them larger than those cut by Oncideres twig girdlers.[2] |
| Twig pruner | The Forest Service handbook notes that stems cut by the hickory spiral borer are often larger than those cut by Anelaphus twig pruners. Peel the bark of a spiral-borer stem and you find a long, frass-packed gallery under the bark that spirals inward.[2] |
Where it lives
Throughout the eastern half of the United States, on hickory and pecan. Hickories seem to be preferred, but pecan is readily attacked.[2][1]
Biology and life cycle
Adults emerge from late April to late June, depending on location, and feed on the leaves, chewing notches and irregular holes. Females begin laying eggs 10 to 14 days after they emerge, one at a time near the bases of current-season shoots or in bark crevices on the trunk and branches. Each female lays 2 to 55 eggs over 6 to 8 weeks.[1][2]
The eggs hatch in 3 to 4 weeks and the larvae chew straight into the twigs, making thread-like burrows under the bark. Late in autumn they begin spiral burrows that sever the twigs by winter or spring.[2]
During the second summer the larva mines down under the bark for 8 to 24 inches (20 to 60 cm), packing the burrow with brown frass. In late fall it changes course, cuts a thin ring around the stem and then bores spirally inward until it reaches the center.[2]
The larva then mines back up under the bark for 1 to 3 inches and forms a crescent-shaped pupal chamber, plugged with frass at both ends. It pupates in May and June for about three weeks. One generation takes two years, with new adults emerging in the third year.[1][2]
Damage and signs
- Branches and terminals are severed in late winter and spring. The part above the spiral usually dies before it leafs out, so the injury shows as the rest of the tree comes into leaf, and most severed branches break and fall just before or soon after budbreak. The cut pieces are 0.5 to 2.5 m (about 1.5 to 8 feet) long.[2][1]
- Repeated attacks leave young trees stunted, misshapen, crooked or forked. On large trees heavy damage can reduce nut production and give the tree a ragged, lopsided look. In one North Carolina study, 7 percent of 500 young hickories had part or all of their main stems killed.[1][2]
- Whole stands, groves and nurseries are seldom badly harmed. Serious damage is most likely in plantings next to woods with many heavily infested hickories, and NC State notes that flatheaded borers are hardest on newly planted trees and trees weakened by drought, defoliation or other stress.[2][1]
Health risk
It is a borer of hickory and pecan twigs and stems. Neither NC State nor the Forest Service handbook describes any risk to people.[1][2]
Control
Prevention
For nurseries and young plantings, removing old hickories growing nearby has been suggested, since the worst damage occurs close to heavily infested hickories. Once grubs are tunneling inside the stem they are very difficult to control with insecticides.[2][1]
Sanitation
Collect and destroy fallen severed stems and branches before the adults emerge; this kills the grubs inside them.[1][2]
Traps and physical control
On small trees, prune off dead branches and terminals as soon as the leaves come out in spring, including the small dead twigs that hold first-winter larvae. To be sure of removing the grub, cut 3 or 4 inches below the dead part.[1][2]
Biological control
Five species of small parasitic wasps attack the hickory spiral borer, which may explain why it is usually not a common pest.[1][2]
Common questions
- Why are pecan or hickory branches falling off in spring?
- The hickory spiral borer is a likely cause if the broken end shows a winding cut that runs from the inner bark to the center of the stem, with a frass-packed gallery under the bark leading to it.[2][1]
- Can I spray for hickory spiral borer?
- Insecticides do little once the grubs are inside the stem. NC State recommends collecting fallen stems and pruning out dead twigs and terminals in spring, cutting 3 or 4 inches below the dead part.[1]
- How long does the hickory spiral borer live inside the tree?
- The larvae develop for two growing seasons, and the new adults emerge in the third year.[1][2]
Sources
- NC State Extension, “Hickory Spiral Borer (J. Baker), PDIC factsheet.” content.ces.ncsu.edu/hickory-spiral-borer (accessed 2026-11-09)
- USDA Forest Service, “Guide to Insect Borers in North American Broadleaf Trees and Shrubs, Agriculture Handbook AH-706 (J. D. Solomon, 1995), hickory spiral borer account (as Agrilus arcuatus torquatus), pp. 239-242.” research.fs.usda.gov/treesearch/22150 (accessed 2026-11-09)
- iNaturalist, “Agrilus torquatus taxon page (order and family).” www.inaturalist.org/taxa/1464827 (accessed 2026-11-09)