Elm Root Borer
- Scientific name: Saperda tridentata
- Size: ½ to 5/6th an inch long
- Color: Creamy white with darker brown heads (larvae), black with orange markings (adult)
- Shape: Long, rectangular body with a smaller, squarish head and very long antennae
- Found in: All throughout the United States
What are they?
The elm root borer is a regularly occurring type of beetle that is native to the United States. They are a year-round insect with an exceptionally long active season and the adults can be seen flying from mid-spring to mid-October. Elm root borers are considered a “long horn beetle” which is a nickname given to a type of beetle that has exceptionally long, segmented antennae. They are a species of insect that feed almost exclusively on their preferred plant, from larvae to adult.
How can you tell you have them?
The damage by the elm root borer is sometimes mistaken for the work of other pest species but can be distinguished by sick looking, discolored leaves and small branches. If you see these on your elm trees, it would be worth taking the time to inspect the bark of the tree. The egg-laying females of the species leave very distinctive groupings of bored holes in the surface of the bark. These holes are made by the ovipositer of the female. Within a few days, these holes will be shown to have small lines of reddish frass, or fecal matter, coming out of them. It the elm root borers have been there more a longer period of time, the elm bark may become loose and easy to pull away from the tree. Under the bark, you can see the tunnels that the larvae had borrowed into the wood of the tree.
What kind of environment do they like?
The adult elm root borer prefers to emerge in the mid to late spring and stays active during the warmer months of the year until late October. The larvae spend the colder winter and early spring months inside the bark of their elm tree.
The elm root borer prefers the American elm for it’s host tree, but has been known to feed and live on/in the cedar elm and the slippery elm. They are very species specific for their dietary needs and will not infest or feed on the English elm, which is not a species native to the North American continent. The adults feed on the leaves and stalks of the tree and the larvae feed on inner bark area. The main issue from these pests is that they are opportunist pests, preferring to infest trees that are already weakened through mechanical means or disease, pollution and other insects.
What to do?
The best defense against the elm root borer is a good system of care for the elms on a homeowners’ property. Because these are a wide-spread and very successful species of pest where the elm is concerned, it is important that a tree that is found to be severely infected is removed from the property. While it is regrettable to have to cut down the whole tree, by the time outward signs of the elm root borer’s activity can be spotted by humans, the tree is very likely completely infested with larvae and adults.