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Wednesday, 29 July 2020

The Dreaded, Unwelcome Gypsy Moth - It's Here to Stay

     A few days ago we were sitting on the deck at our friends Alan and Anne Morgan's house, gazing at, and admiring Anne's garden which is a phenomenon to behold, sipping wine and talking of all things under the sun.
     At some point our attention was rivetted on a female Gypsy Moth (Lymantria dispar) on an oak tree (Quercus sp) and the conversation quickly changed to this invasive insect, which is present in seemingly apocalyptic numbers this year. I know that memory is selective, but I cannot recall seeing Gypsy Moths in such profusion.
     Having been introduced to North America in 1869 in Boston, it has become a serious pest and is capable of deforesting vast areas of native woodland. Stephen Marshall recounts an incident where he was seated under a tree at a picnic table and was driven away by the pitter-patter of frass (bug poop) falling from the caterpillars on the branches above onto the table and into his coffee!


     Let me try to give you a little more insight into this entirely unwelcome guest.

Hosts: Gypsy Moth caterpillars are especially fond of oak and aspen, but will opportunistically feed on other species as diverse as Hemlock, White Pine and Poison Ivy. The picture below shows females, egg masses, larvae and pupa on a Norway Maple.


Damage: The larvae chew the leaves of their host plants during the spring, and the noise of an army of these creatures can become quite loud. Gypsy Moth is an outbreak species, sometimes persisting for two or three years, during which time trees can be seriously weakened and vulnerable to other pests such as the Two-lined Chestnut Borer (Agrilus bilineatus).

Distribution: Currently found over much of Eastern and Central Canada, the Northern U.S. as far west as Minnesota, and south to the The Carolinas. Isolated infestations have occurred in other regions when eggs have been transferred on plant materials.


Appearance: Larvae are generally mottled grey and have pairs of coloured tubercules. The hairs on the body can be irritating to human skin. Male moths are dark brown with wavy darker markings across the wings. Females are flightless despite having wings that are white with wavy stripes.

Unmated female
Life History and Habits: The eggs overwinter in a mass covered with hairs from the body of the female. Exposure to cold is a requirement for egg development. Eggs usually hatch in April and the young larvae move to the tips of branches where they may be dispersed by the wind (ballooning). Males go through five larval instars, females six, over the course of about six weeks. Feeding occurs at night with the larvae moving to branches and trunks during the day to rest and moult. During serious outbreaks daytime feeding also occurs. 

Caterpillars with chrysalids
     The larvae may settle on plants for pupation but will also wander and settle on rocks, other vegetation, upright surface of buildings or other convenient locations. Adults emerge about two weeks later. The male is a strong flyer but as noted above the female is flightless. 
     After mating, females lay a single egg mass, typically containing 250 eggs. 

Copulation

     The Gypsy Moth is a notoriously variable species and the Siberian Moth (Dendrolimus sibiricus) differs from the European Gypsy Moths in some sinister ways. The females are able to fly and they have a taste for conifers which are the lifeblood of the western forest industry. Not surprisingly the appearance of of the Siberian Moth in British Columbia has caused great consternation and aggressive actions to control or eradicate it.

Photo creditAll of the photographs were taken by Alan Morgan, to whom I owe much gratitude for his permission to use them on my blog.

References

Cranshaw, Whitney and David Shetlar, Garden Insects of North America Second Edition, Princeton University Press ((2018)

Marshall, Stephen A., Insects - Their Natural History and Diversity, Firefly Books (2006)

Milne, Lorus and Margery, National Audubon Guide to Insects and Spiders, Chanticleer Press Inc. (1980)

Stanek, V. J., The Pictorial Encyclopedia of Insects, The Hamlyn Publishing Group Limited (1969)    





79 comments:

  1. Oops. It's the part of nature I am not so fond of.

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  2. We used to know the Morgans when we lived in Guelph.

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  3. Apparently we had Gypsy moths (Lymantria dispar) living here, but they became extinct in 1900. However, apparently a small European population was discovered in June 1995 in north-east London, near Epping Forest. It is thought that it arrived from mainland Europe via vehicles, wooden packaging and/or imported timber. It has now spread to much of London and parts of South-East England.
    What it is doing in Canada sounds really horrific.

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    1. This is an outbreak year, Rosemary and it can be devastating. The woodlot at SpruceHaven has been substantially defoliated.

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  4. Hi David thankyou for the interesting post,not sure we have these in Australia but we do have caterpillars,hope your day is a good one.

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    1. I am quite sure they are not present in Australia.

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  5. Thanks for the information. Oh my...

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  6. I drove over much of the eastern US in the nineties and early 2000'nds. Watching the spread of this pest and the deforestation was heartbreaking. Ditto the emerald ash borer.

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  7. Good evening, dear friend and professor David, how are you!
    it is said that the thrushes and venteveos do a good cleaning of these worms... i don't know... will it be like this?
    Abrazo afectuoso, bye bye

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    1. Very few birds are able to consume this species. Here in southern Ontario it is restricted to Black-billed and Yellow-billed Cuckoos and they do not have a serious impact.

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  8. Oh dear. They are very unwelcome in my garden.

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  9. These Gypsy Moths sound dreadful. It helps one understand better as to why our border controls are so important in preventing pests of all kinds entering the country (they are not always successful, unfortunately).

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  10. Oh they really are terrible .... devastation a few years ago (I lose track) here in Oregon forests.... but I guess I thought the theat was over because I hadn’t heard anything for some time. There used to be little traps hanging on some trees in the woods ...little triangular boxes. ..... I hope they’re able to control these ugly things.

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  11. David - thanks for the information. I will keep my eyes peeled in Montana!

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  12. After reading this post I "googled" gypsy moth in New Zealand and read that in 2003, we found the moth in Hamilton. It was declared eradicated in 2005. We have a surveillance network monitoring for this moth near our borders. I just hope it stays away.

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  13. Hi David. These are nasty creatures. We have them here, too, and have to report them to the authorities so they can destroy them, as they cause a lot of allergies as well as the damage to the trees. Things like this are hard to control! Have a great day, take care, hugs, Valerie

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  14. I know people put out special traps for them.

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  15. Hello David! Great series of pictures!
    Yes,we have these in Greece ,and mostly on pine trees!
    Thank you for sharing all those interesting informations!
    Have a lovely day!
    Dimi...

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  16. Fascinating post! Those caterpillars give me the heebie-jeebies! EEK!

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  17. Interesting to say the least.
    They sure do make a mess and plenty of them it seems.
    Many times introduced species do more harm than good in the long run.
    Take care.

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    1. I cannot think of an introduction that has produced a net benefit. In the case of Australia, just think of rabbits, foxes and Cane Toads.

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  18. Hello David, nasty this invasion of this kind of caterpillars. We have the same problem over here with the Thaumetopoea processionea. Also living on Oak trees. Is it family of the ones that you find in your region? LuckeleytThis year there are less.
    Regards,
    Roos

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  19. C'est un peu comme nos chenilles processionnaires qui font mourir les conifères et qui sont dangereuses car poils très très urticants...
    Bonne journée

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  20. Oh, it's a creepy bug, David. I hope it will be gone soon, but probably not. We have similar problems here with Yponomeuta evonymella.

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    1. WE are going to solve our problem by exporting them all to Norway, Marit!!

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  21. Hello, David,

    They are dreaded, they have done much damage around here. Mostly to oak trees, very sad. I think they have sprayed some areas. Take care,stay safe! Have a great day!

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    1. The problem seems to be, Eileen, that some of the caterpillars do not succumb to the chemical spray and become resistant to it, so that the next generation inherits immunity. This has been an all too familiar story with pesticide spraying.

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  22. Thank you for this informative post. It's unfortunate that they don't seem to have a predator that eats them. And once again, an imbalance in nature can be traced to humankind as the cause.

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    1. Thanks for a great serious of informed, thoughtful comments, Anne.

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  23. Wow!!Soo many moths!!!Wow!!Here I have seen only a few in my home but at work there are some more(Hospital with much nature around)
    They look beautiful but i quess they make alot of trouble!

    Wish you a great day!

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  24. Hi David, I'm glad I found your blog.
    Thanks for telling us about this creepy invasion.
    I love butterflies, dragonflies, etc.

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  25. I'm caught up on your posts David...so much to take in! I especially enjoyed reading about Verda's wonderful gift to you- a better home they could not find. I wish I had had that wonderful nature magazine along with my Highlights when I was a girl.

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  26. Una plaga devastadora amigo David. Hoy día con tanta facilidad de trasladar plantas y árboles desde cualquier parte del mundo a otro lugar se facilita el transportar de ciertas plagas muy dañinas de un lugar a otro. El mercado debería ser muy exigente con ciertas exportaciones e importaciones para que ciertos casos tan dañinos de plagas no se pudieran producir.
    Un fuerte abrazo de tu amigo y compadre Juan.

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  27. The leaves will suffer. The caterpillar army will grow.

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  28. Hi David, beautiful photo on your header. Beautiful bird. I don't like unwelcome guests but beautiful photos.

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  29. Wow, thanks for sharing this information. I haven't seen them here.

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  30. Amazing how well camouflaged they are on the tree bark. The shrews and white tailed mice will doing a happy dance when they hear about that invasion/feast!

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  31. I'd never heard of them before this year but at one of my Zoom Alzheimer meeting somebody mentioned them and said how much damage they were doing locally. I know it's nature and all that, but they are still horrid things. Thanks for the detailed information.

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  32. Awful how much harm they can do.

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  33. They are pretty scary. I found one, but I think there are more trees involved. There is an infestation nearby, on the lake.
    A very informative post. Some days I just cannot cope.

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  34. Your publication is very interesting. Around here I have seen on certain occasions a proliferation of similar caterpillars in certain trees, now I learned that they are from this family of moths

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  35. that must be what has been flying around our porch. There are two or three or more we see but they haven't stopped enough to get an id on them. I bet that's the deal. Rats....

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    1. The males hardly ever seem to land, Jeanie, but the females are easily spotted on the trees if they are present.

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  36. I read a book about invasive species recently ("Where Do Camels Belong?" by Ken Thompson) and one thing is abundantly clear - we know very little about the subject!
    As for an introduction that has been of some benefit, Dr Thompson would ask: how about wheat?

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  37. Hi David - I see it's not a notifiable pest here. It was extinct ... but has been brought in possible from over the Channel/North Sea etc ... and is now spreading around. It's not reportable ... but if there's an outbreak then anyone who spots the outbreak should notify TreeAlert. It's native to Europe ... but not to us per se - it became extinct in the 1900s and used to feed on bog myrtle and creeping willow ... so when the Fens were drained - that let them become extinct.

    I'm pleased John commented above ... I've noted his book recommendations - they'll make interesting reading. Take care ... Hilary

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  38. I'd never seen these Gypsy moths, David. In fact they are beasts.

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  39. While I have always known of the destruction the gypsy moths cause, your photos and information make that all the more clear, David. I can see no good reason for not eradicating them whenever possible and the trees will be happier. Are there any insects or animals that devour these pests?

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  40. Muy interesante David. Por aquí tenemos una muy parecida Thaumetopoea pityocampa, procesionaria del pino y como bien dice su nombre el árbol que más le gusta es el pino. Un abrazo querido amigo.

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    1. A few bird species, Beatrice, especially our native cuckoos, and deer mice and shrews, and a few other small mammals, but in a year of infestation such as 2020 the sheer volume of caterpillars overwhelms all predators.

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  41. ...in the past the Gypsy Moth was a serious insect pest and then they seemed to disappear. Now they are making a comeback. Thanks for joining the party, please take them along with you!

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  42. I didn't know they were that destructive.

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  43. I think I read about this pest in Rachel Carson's Silent Spring.

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    1. Indeed you did, Judy, on pages 156-61, and 285-86. If I were the head of the Great Church of Nature, Rachel Carson would be the highest saint in the order!

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  44. We seem to have missed out on the Gypsy moth here in Southeast Texas so far, but it may just be a matter of time.

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  45. I didn't realise they were that destructive!

    All the best Jan

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  46. Hi David,
    I'm so sorry this gypsy moth, that seems rather harmless at our side of the world, is ruïning so much trees in your country.

    Best regards, Corrie

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  47. Well! This was a revelation. When I see "Gypsy Moth," the first thing that comes to mind is the 53' ketch that Sir Francis Chichester commissioned for his single-handed sail around the globe. He spelled the name differently (Gipsy Moth) but he didn't cause nearly the trouble that this insect has brought about; he broke different sorts of records.

    I see that this troublemaker's generally confined to the northeastern U.S. It isn't shown in Texas. We have our problems with invasives and introduced species, but this isn't one. Still, it's quite a cautionary tale. It's a shame there isn't biological control available.

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  48. The moth is kind of pretty in a way but the larva etc..not so much. It's sad that they are so destructive.

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  49. Hi David,
    Invasive animals of all kind can be a real threat for the nature where they show up. Sometimes their behaviour is devastating. Climate changes, behaviour of men can be the reason of their appearance. Think for instance of the influence of rabbits in Australia. Moths and their caterpillars may look nice, but sometimes you prefer them disappearing asap.
    Greetings, Kees

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  50. Hoi David,

    Ondanks dat het (blijkbaar) een schadelijke en invasieve soort is heb ik in Nederland nooit zulke verhalen over deze soort gehoord. Hij komt hier wel voor en ik vind de vlinders wel mooi om te zien maar als ik er honderden of duizenden zou zien zou ik ook gaan twijfelen of dat wel goed is voor de flora.
    Wij hebben in Nederland jaarlijks veel last van de eikenprocessierups (Thaumetopoea processionea) die dezelfde klachten en schade veroorzaakt. Ze werden / worden vaak met gif besteden wat leidde tot vergiftigde of mezen. Gelukkig zijn er nu gemeentes die ze natuurlijk proberen te bestrijden door middel van zuigen of het inzetten van mezen.
    Hopelijk wordt het natuurlijk evenwicht ooit weer hersteld als iedereen daar eens over zou nadenken...

    Hartelijke groet,
    Marianne

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    1. Always a pleasure to hear from you, Marianne. In Europe, where the Gypsy Moth originated, I am sure that a whole range of conditions found there keep it in balance, predators, climatic influences, seasonality, host resistance and so on, but when it is introduced to an area where those normal checks are absent it goes crazy! And it certainly has done so here!

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  51. Hello David,
    It is sad to see how much destruction these Gypsy Moths leave behind. Hubby and I have seen the dead trees in our neighborhood and in the national parks. Great post and information.
    Thank you for linking up and sharing your post. Enjoy your day, have a great weekend! PS, thanks for visiting my blog and for the comment.

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  52. You are a wealth of information! This was interesting learning more about these moths. I stood next to a big web and took pics of hundreds of crawling caterpillars inside the web just yesterday. I was fascinated! (and trying out my new camera) Happy weekend!

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  53. Sorry for the late arrival at your blog, David - too many distractions at present, but they are diminishing, it seems!

    I'm not sure that I'm on the correct blog anyway - the David that I know doesn't 'do moths'! This person seems a lot more knowledgeable than I am on the subject.

    Whilst the Gypsy Moth can be a nuisance in the south-east of England, I do not believe it has reached this area - yet! However, we used to have it here, but it is now considered 'extinct' in the county. I hope it stays that way!

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  54. Interesting post. It seems I've seen those caterpillars around here though not lately. I'll have to keep an eye out especially at work where the kids are constantly showing us interesting creatures. Hope you are enjoying your weekend.

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    1. If you have any kind of infestation in your area you will certainly see them, and probably hear them too.

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  55. Now THIS is creepy! I don't like seeing these numbers of such, but I guess they serve a purpose somehow.
    Thanks so much for sharing your part of the world of nature near you with us at IRBB this week. It's always appreciated.

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  56. I looked up the following : It seems it is our fault!!
    It was introduced to the United States in 1869 when French artist, astronomer, and amateur entomologist Leopold Trouvelot imported some eggs of this species to Medford, Massachusetts, with the idea of breeding a silk-spinning caterpillar that was more resistant to disease than the domesticated silkworm. Unfortunately, the caterpillars escaped into his backyard. About 10 years later, they began to appear in large swarms, and by the late 1880s they were causing severe defoliation in the area.
    Keep safe and take care, enjoy the week, Diane

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  57. We've an infestation on the lake, nearby. I found one caterpillar, so I'm sure they are here.
    I hope, like tent caterpillars, this is just a wave and will pass.
    Do they birds eat them?

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    1. Most birds avoid them due to the mild toxicity in the spines, but Black-billed and Yellow-billed Cuckoos relish them.

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  58. Those moths are obviously devastating. We have our own history of introduced pests in Australia. Some idiot thought introducing rabbits was a good idea and they became a disastrous pest currently being controlled by calicivirus. Currently the state I'm in is trying to stop the invasion of cane toads which were introduced to deal with pests in the Queensland cane fields any years ago and have moved inexorably across the north of the country. We never seem to learn, do we.

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    1. We don't learn do we? Often the attempted cure only makes the situation worse too.

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  59. :( Our forests are infected with European spruce bark beetle, seems to be a similar problem :( Not fun at all.

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