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Western Tussock Moth
Western tussock moth caterpillars can defoliate a tree in record time and they are wreaking havoc in many regions.
There are over 2,500 species of tussock moth (Lymantriinae) worldwide. The family name Lymantriinae comes to us from the Latin word for ‘defiler’. Cousin to the gypsy moth of East Coast nightmares. the western tussock moth is making itself felt west of the Rockies.
Western tussock moth caterpillars feed on leaves and young fruit. What makes these pests so much of a threat is how much and how fast they eat. Western tussock moth larva, or caterpillars, will feed heavily on apple, apricot, cherry, citrus, pistachio, plum, and prune trees, as well as many ornamentals, such as oak, ceanothus, and willow.
Western tussock moths (Orgyia vetusta, formally known as Hemerocampa vetusta) are normally present in this area, being native to the west coast of North America, but chilly winter weather and natural predators usually keep their numbers limited. Warmer winter weather allows these moths have a boom population, and 2018 is one of those years.
Currently, local parks and walking trails are finding trees, sidewalks, and park equipment covered with these caterpillars. Caterpillars are falling out of trees onto cars and people, there are so many of them. Newly hatched caterpillars have a habit of using a silk thread to balloon themselves to a new location. Walking into a cloud of ballooning caterpillars isn’t something most people enjoy.
Western tussock moth description
These pests are easy to identify. A Western tussock moth caterpillar is 1-1/2 to 2 inches long and features white tufts (called pencils) that stick up along the back, with two black tufts on its head, and one on its read end. They also have paler tufts along their entire length and sides. You will also see bright red and orange spots. The adult female moth is unique in that she does not fly. She is short-winged (brachypterous) and stays with the cocoon. She is a pale gray color, but you probably won’t see her. The males find her because of chemical scents, called pheromones, that she releases. The male moth does have wings. He also has prominent, fringed antennae. He may be dark or light brown, depending on the local environment, with black and white markings. Larva go through several stages, called instars. Until they reach their full size, they are black, with black hair pencils on their first four abdominal segments.
Western tussock moth lifecycle
Adult moths do not feed. Each female moth lays hundreds of eggs. Eggs are laid directly on the cocoon. The female moth covers the eggs with a protective coating and then covers that with a camouflaging layer of hairs (setae) from her own body. The eggs overwinter in this protected state and then hatch in spring through mid-summera. These caterpillars feed intensely for 40 to 60 days before pupating. While the caterpillars of some tussock moth species spread an irritant on the setae (hairs) that cover their bodies, the western tussock moth does not fall in that group, but they can be a pain, nonetheless.
Western tussock moth controls
Local governments use several methods to control heavy infestations of western tussock moth caterpillars:
Hopefully, your garden and landscape will be spared a visit from the western tussock moth. If you are not so lucky, you can spray Bacillus thuringiensis (Bt) to deter these pests. If a severe infestation does occur, you may have to prune out heavily affected limbs.
7/11/2019 09:57:25 am
I live in Eastern Washington state and the tossock moths are attacking our fir trees. We are currently having them sprayed and they are falling out of the trees. I know we can't get them all but hope to thin out the herd. I have been doing some research and I can yet find out what happens to the male moth. It states the female dies after she lays eggs. Any input or knowledge of the male moth?
7/12/2019 06:02:46 am
7/12/2019 09:00:46 am
7/15/2019 06:24:05 am
7/15/2019 07:13:33 am
Thank you for your reply. What I have read the female moths die after laying their eggs. But no where can I find the life cycle of the male moth. Hopefully we can get a handle on the cocoons to minimize another hatching before winter sets in. What I understand also is that the eggs cocooned by the female can survive winters unless there is 0 degrees and under for a couple of weeks. Therefore the cycle repeats itself until predators, weather etc. ends the cycle for a few years 2 to 4 what I have read. Then 10 years later it repeats itself. Animals, insects, etc. amazing how they strive to survive. Also have watched them on the outside of our cabin as caterpillars and slowly cocooning themselves. Will keep an eye on them and see how long it takes to turn into moths. Those are the only 2 I will keep an eye on!!
7/16/2019 05:22:54 am
All those processes really are amazing, aren't they? Even when we're talking about pests. The more I learn about what's going on in my garden, the more I realize just how little I saw before I started looking more closely.
6/9/2022 11:46:01 pm
Hi, I live in south east England and I saw one of theese caterpilars just the other day. I am very sure that it was this species and am wondering how this may be possible, is this due to climate change? Thanks
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