These destructive tree insects are hardly detectable at first sight, however over time as it begins reproducing; it creates a cottony-like substance easily seen in tree joints. Some tree insects are beneficial, assisting in pollination and population control of other insect species, but there are some that can be destructive. The best strategy for this invasive insect is prevention, because once the tree insect is discovered it’s usually too late to save the tree.

Hiding in Plain Sight: Common Signs of Insect Invaders

Most tree pests leave visible signs of their presence – if you know what to look for.

Sometimes it’s easy to dismiss these observable symptoms. After all, it’s just a few tiny holes in the trunk or slight withering of the foliage. Unfortunately, as an infestation worsens, the plant material deteriorates and the overall appearance of the landscape suffers. In some cases, the problem may progress to a point where the plant cannot be brought back to health. The only option then becomes removal and replacement.

It’s always easier to prevent an unsightly or destructive issue instead of waiting for it to happen and then reacting after the fact. But when your list of ‘should-dos’ is long and your budget short, treatments to suppress insects don’t always make the cut. With that in mind, understanding the types of pests that impact trees and shrubs, as well as the associated symptoms, can help ensure infestations are identified before irreparable damage is done.

Boring Insects

Considered the most destructive pests of ornamental trees and shrubs, these insects tunnel inside the tree feeding on the inner bark. Though external evidence may be minimal, especially in the early years of an infestation, devastating internal injuries make it impossible for the tree to transport water and nutrients. Boring insects are often (though not always) secondary invaders, attacking a tree that is already under stress.


  • Exit holes in the trunk or branches
  • Sawdust-like debris or frass
  • Loss of leaves

Notable Pests

  • Emerald Ash Borer
  • Asian Longhorned Beetle
  • Ambrosia Beetle
  • Bronze Birch Borer
  • Two-lined Chestnut Borer
  • Weevils and Bark Beetles

Chewing Insects

Unsightly feeding damage is the hallmark of insects that consume leaves or needles and the results of their presence can be a noticeable blemish on an otherwise beautiful property. Minor defoliation is typically not a serious problem for otherwise healthy trees. However, a severe infestation or repeated loss of leaf surface over several years can significantly reduce a plant’s ability to grow and thrive.


  • Nests or the insects themselves
  • Holes in leaves
  • Skeletonization or the complete removal of leaf tissue
  • Unseasonable loss of leaves

Notable Pests

  • Winter Moth
  • Gypsy Moth
  • Tent Caterpillars
  • Oak Processionary Moth
  • Webworms
  • Oakworm
  • Cankerworm
  • Leaf Beetles and Leaf Miners

Sucking Insects

A number of insects survive by sucking sap and nutrients from the plant with tiny, needle-like mouthparts. Given their small size, these pests may go undetected for years, building a damaging population over time that could have easily been prevented. Nearly all types of woody ornamentals are at risk of infestation by some type of pest in this category.


  • Withered leaves
  • Branch and tip dieback
  • Loss of needles or premature leaf drop
  • The presence of sticky sap or honeydew
  • A coating of sooty mold

Notable Pests

  • Mites
  • Scales
  • Aphids
  • Whiteflies
  • Psyllids
  • Adelgids (e.g., Hemlock Wooly Adelgid, Spruce Gall Adelgid)

Insect prevention is critical in protecting homes, businesses, schools and any other place where human beings live, work or play from a pest infestation.