1. Introduction
  2. Types of Biological Controls
  3. What HRI is Doing
  4. What Others are Doing
  5. HWA Predator Monitoring at Home

HWA Predator Monitoring at Home


Laricobius nigrinus eating hemlock woolly adelgid. Photo by John D. Simmons

Table of Contents



North Carolina’s Hemlock Restoration Initiative (HRI) is one of several programs (governmental, academic, non-profit) throughout the range of eastern hemlock actively working to establish biological controls of hemlock woolly adelgid (HWA). The HWA biological control program operates under the guidance of the USDA Forest Service Forest Health Protection program with oversight from a federal regulatory agency called APHIS (Animal & Plant Health Inspection Service).

While a number of predator insects have been released to control HWA, and more are currently being evaluated, two species of Laricobius beetles shows particular promise. Unlike most predator beetles of HWA, Laricobius is a winter feeder. Both the adult and the larvae feed on HWA from November to May. The adults consume adelgids before laying their eggs singly in HWA egg sacs. Each Laricobius larva consumes HWA eggs or crawlers before it pupates in late spring.

Thousands of Laricobius beetles have been released in North Carolina since 2003. In that time, they have become increasingly easy to recover and are now being found many miles from their original release sites. These predators are clearly reproducing and redistributing themselves throughout the landscape, evidence that they are becoming established. It is likely that Laricobius beetles are present on many private lands throughout western North Carolina. Understanding where Laricobius are and how they are spreading will help to inform the hemlock management decisions of private citizens, governments, and organizations, like HRI and its partners.

The following instructions are intended to help home owners and land managers determine whether these beneficial insects are present on their properties and what effects their presence is having on HWA populations and the overall health of their hemlocks.

Please note: these instructions are for monitoring for Laricobius only; other predators will have a different monitoring protocol.

Considerations: Before you get started

  • No Trespassing! All monitoring must take place on your own private lands or with landowner permission; this includes all public lands.
  • Determine whether it is likely that you will find Laricobius beetles on your property. Consult the Virginia Tech/USDA Forest Service HWA Predator Database to find the release site nearest you. This database is not exhaustive and may not include every Laricobius release site, but it can give you a sense of the densities in your area.  The closer you are to a release site, the more likely you are to find them; however, beetles are being recovered increasingly far from release sites and may still be present on your property even if you are located some distance away.
  • Where to monitor: You are more likely to recover Laricobius in an area that has numerous hemlocks infested with HWA.  Hedge rows and forest edges are excellent places to look for them. Target branches that are in open areas receiving sun and are infested with HWA; this is usually where the beetles are. Trees that are currently chemically protected are less likely to have beetles (if no living HWA is present, there is nothing for Laricobius to feed on and they will move to other areas).
  • When to monitor: The best time to monitor for Laricobius is November through April. November-February you are more likely to find adult beetles, March-April you are more likely to find larvae. As spring progresses, beetle larvae will drop down into the duff layer to pupate. It is extremely unlikely that you will locate Laricobius  during summer months. Search for beetles on warmer sunny days. Do not attempt to monitor under adverse weather conditions (e.g. heavy wind, rain, or temperatures below freezing). Sunny days with temperatures above 45°F, between 10am and 4pm are the best times to recover beetles.


Before monitoring for Laricobius you will need to prepare the following:

  1. Long pole to tap/”beat” hemlock branches
  2. “Beat sheet” (large, light-color fabric with rigidity, such as a canvas sheet on a wooden frame)–purchase here, or make your own
  3. Data recording sheet (download HRI data sheet here) and pen/pencil
  4. Hand lens or other magnifier
  5. Bright light source, such as a flashlight or lighted hand lens
  6. Aspirator and 10 dram vials which can be purchased here
  7. Flagging tape, tree tags, or GPS to mark monitoring site and individual trees
  8. Measuring tape to find each tree’s diameter
  9. Camera/cell phone to record release site and tree condition
  10. Thumb counter to record number of beetles recovered (optional)
  11. UV light (optional)

Monitoring Instructions

Before you start

The protocol for monitoring for Laricobius beetles is simple. However, accurate identification of Laricobius to genus and species is often the most challenging aspect as beetles are small (about the size of a sesame seed), unassuming, and can be difficult to distinguish from other native beetles.  This guide provides instructions for home identification of Laricobius beetles to the genus level. Several different species in the Laricobius genus feed on HWA to varying degrees, but identification to the species level is very difficult to verify without genetic analysis. If you would like to attempt the additional challenge of identifying to the species level, HRI is interested to hear about what you find. Photos below show the three species of Laricobius you are likely to encounter. You can click here to learn more about the differences between Laricobius species. 

Before you begin, consider which beetle life stage you are likely to encounter (November- February = adult beetles, March- April = larvae and adult beetles).  Note: Summer months (June- October) are not suitable for beetle monitoring as Laricobius beetles are pupating in the soil during this time. See more information about the Laricobius lifecycle on our Types of Biological Control page.

Hemlock twig with HWA under black light (orange color is beetle frass, chartreuse color is adelgid hemolymph)

You may also use a UV light to reveal possible beetle activity. When a UV light shines on a hemlock branch in complete darkness, HWA blood may appear as dots of a yellow-green color and Laricobius beetle frass may appear as orange. While seeing these colors during a UV examination of hemlock branches is not a guarantee that beetles are present on your tree, it is a sign that further monitoring and observation may prove fruitful. For more information about this UV light technique, view a report on the subject here.

Prepare for beetle monitoring by reviewing photos of Laricobius adults and larvae as well as the data collection sheet so you know what you are looking for and what type of information you will need to gather. To be 100% sure you are correctly identifying Laricobius, collect 1-2 specimens and send to HRI (instructions below).

Source: T. McAvoy et al. “2019/2020 Recovery Protocols for Laricobius spp. and Sasajiscymnus tsugae “ (2019) Virginia Tech

Life stages of Laricobius osakensis

Laricobius osakensis life stages. (A) Adult female, (B) adult male, (C) two eggs beside dead adult HWA, and (D) fourth instar larva feeding on HWA eggs. From Lamb, et al. 2011. “Chapter 7: Laricobius oaskaensis, a hemlock woolly adelgid predator from Japan.” FHTET-2011-04

Common look-alikes to adult Laricobius nigrinus
1. Purple scale predator 2. Bark weevil 3. Springtail 4. Chilocorus beetle

In the field

  1. Prior to beetle monitoring, choose which trees you will be sampling.
    • Working one tree at a time, measure and record tree diameter 4.5 feet above ground, mark (tree tags, paint etc.), photograph (if possible), and record tree condition on your data sheet. Collecting this data will allow you to track tree health and predator beetle populations over time.
    • Prepare your specimen collection vial by placing hemlock twigs infested with HWA in the plastic vial with the aspirator.

Aspirator attached to collection vial

  1. Focus on branches with HWA.
    • Visually examine the HWA ovisacs before beating to look for signs of disturbance. Ovisacs that have been visited by beetles may appear torn open or teased apart. Undisturbed ovisacs will look more like round cotton balls. While this is not a guarantee that beetles are present, it is a sign that further monitoring and observation may prove fruitful.

Hemlock branch with disturbed HWA ovisacs

    • Put the beat sheet under the branch to catch any falling beetles. Most beetles will dislodge easily from trees so avoid brushing or otherwise disturbing branches of the trees to be sampled until the beat sheet is in position to collect falling beetles.
  1. Tap the branch smartly with the stick 5-10 times above the beat sheet, keeping the sheet directly under the branch.
    • You should tap hard enough to dislodge beetles, but not so hard that the branch bounces away from the sheet.
    • Sample 8 branches per tree (2 branches in each compass direction) whenever possible. If all the branches are on one side, then sample only those branches.


  1. Scan the beat sheet for Laricobius, remembering to look on/under leaves, twigs and needles for beetles hiding in the debris.


  1. Count the total number of Laricobius beetles you find (a thumb counter can be helpful to keep track). Record your findings and other data on the data collection sheet (download here). All data is good data, record findings even if no beetles are found.
  2. Use the aspirator to collect 1-2 specimens of each beetle you believe to be a unique Laricobius species.

  1. After counting, recording and sampling insects on your beat sheet, gently dump the remaining insects and debris at the base of tree so that beetles can return to their prior location on the tree.
  1. Using the same protocol, sample 9 more neighboring hemlock trees that have healthy HWA.
  1. Record your data by submitting data sheets to HRI

For accurate insect identification, submit samples (in plastic vials) to HRI by mail at the address above.

If you do not find any Laricobius after the first try, try again on another day. It can take substantial effort and several attempts to recover any.

Frequently Asked Questions

  1. What do I do with the data I record?
  2. How do I know if I have “enough” beetles on my trees?
  3. How can I get practice identifying Laricobius beetles?
  4. How do I monitor the health of my tree over time (whether beetles are present or not)?

What do I do with the data I record?

  • Submit your completed data sheets to HRI via email:  info@savehmelocksnc.org or via mail: 594 Brevard Rd. Asheville, NC 28806. Home monitoring data is extremely useful for HRI, as it allows us to expand our knowledge of where HWA predator beetles are and aren’t present, as well as their densities, which in turn helps direct our management activities. We conduct our own beetle monitoring program, but with limited staff capacity and without access to many hemlocks on private property, we can only do so much. Therefore, landowners who take the initiative to monitor for beetles on their own property and who share that information with us are a huge asset in broadening our understanding of the current status of HWA predators in western North Carolina. We also provide compiled reports on our collective findings, which can inform research and influence future funding for biological control.
  • Use what you find to inform management decisions on your property. For example, if you find lots of beetles that you are positively able to identify as Laricobius and hemlocks are currently healthy, you may decide not to chemically treat your trees immediately but, instead, to continue to monitor tree health and predator populations. Conversely, if few to no beetles are present you may choose to treat your trees in order to prevent decline or to treat a subset of trees–protecting the most valuable ones while others remain untreated and may attract beetles in the future.

How do I know if I have “enough” beetles on my trees?

  • Studies are currently underway to measure the level of predation of Laricobius on HWA. It is still unknown how many beetles are “enough” to protect a tree or a stand of trees from HWA damage. At this time, chemical treatment remains the only known way to protect an individual tree from HWA and halt decline.
  • The primary goals for home beetle monitoring are:
    • To determine whether beetles are present on your property and use this information to inform your hemlock management decisions
    • To share your data to inform research

How can I get practice identifying Laricobius beetles?

  • The Hemlock Restoration Initiative occasionally holds beetle monitoring volunteer work days.  You can sign up to volunteer and we will notify you about monitoring days.  Be sure to indicate that you are interested in beetle monitoring.  This is a great way to learn the procedure and get better at identifying the beetles.
  • The Hemlock Restoration Initiative holds training workshops for landowners to learn about protecting their hemlocks. These workshops may include instructions and hands-on practice with biological control monitoring. To hear about future workshops, sign up for our e-mail list and be sure to indicate your interest in HWA predator monitoring.

How do I monitor the health of my tree over time (whether beetles are present or not)?

  • Take photographs over time.  This will give you a visual record to keep track of your tree’s health.
  • Keep an eye on the lower branches–trees declining from HWA tend to lose lower branches first and slowly die from the bottom up. Branches that have lost their needles but still show fine twig structure are an indication that needles were lost recently, likely due to HWA.
  • Check the reachable branches for HWA. How heavy is the infestation? (See photos below.) During winter months, look for white woolly egg sacs at the base of each hemlock needle. If the tree is heavily infested (egg sack at the base of most of the needles) it is likely to decline more rapidly. If the tree is lightly infested (egg sacks at the base of a few needles) the tree may be less stressed by HWA.


New spring growth (light green) at the tips of hemlock branches

  • Look for new growth in the spring (right). New growth appears on hemlocks from February to May and appears as soft, bright or light green tips on branches. New growth is a sign of hemlock health, the more new growth each spring, the healthier the tree.
  • If a tree remains relatively healthy over time, continue to monitor its health and look for predator insects. If a tree is in rapid decline, chemical treatment may be the best option to save it.

Thank you to the Blue Ridge Resource Conservation & Development Council for assistance with compiling this information.

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