When it's Man against Caterpillar

It's time for an entomology lesson, as we explore the life and times of this cutie, now having a banner year in our gardens.  The evidence for that is all around me and in the chatter on the local horticulture listserv.

LIFE CYCLE OF THE EASTERN TENT CATERPILLAR (Malacosoma americanum)

1. In early summer females lay masses of 150-400 eggs in sticky, black masses in trees.  They stay there about 9 months.  Just like humans.
   
2. In early spring caterpillars (the larvae) hatch, just as the host plants are leafing out, often on their preferred host, the cherry tree.  They feed on the new leaves and start forming truly disgusting-looking tents or webs for shelter at night and during heavy rains.  The tents get bigger and bigger as the little buggers feed and can eventually be 2 feet long.
3. After about 6 weeks of feeding, they wander off to find suitable spots to pupate (spin cocoons), spots like under bark or in a rolled-up leaf, even in the tent itself (or, as I discovered just yesterday, inside our gardening gloves.  Gross!)  They'll cross roads, sidewalks and lawns in their search.
4. After about three weeks (in July) the moths emerge from the cocoons, mate, lay eggs and die.  There's one generation each year (unlike, say Monarch butterflies, which produce many generations every year).  These small moths, with a wingspread of only an inch, only live a few days and don't feed at all (they're too busy getting it on).

PITY THE UGLY
All the authorities say these critters can defoliate plants but rarely kill them, so why should humans care one way or the other?  Well, they're accused of being unsightly - an accusation that I find wholly accurate.  But is unsightliness a crime punishable by extermination?  And one academic site even accused them of causing "a high level of aggravation for people trying to control the wriggling masses of larvae."  Sure, they're creepy but "high level of aggravation"?  Get over it. 

So how do humans combat the source of their aggravation?

• Smart gardeners notice the tents in early spring and go after them - by pruning them out or poking through them with a stick.  A good dousing from the business end of a high-pressure hose may also do the trick.

• Burning the tents is a common practice that's advised against by the authorities.  As one listserv member put it:  "I simply can't imagine climbing around in a tree and wielding a torch very effectively, plus you might well have a nasty accident."  Right.

• Some Extension Service sites suggest killing young caterpillars with an insecticide containing Bacillus thuringiensis var kurstaki or insecticides like carbaryl, methoxychlor, and malathion. They don't exactly say how, except that spraying the tents is pointless because the caterpillars are well protected in them.  But really, shouldn't these educational institutions be presenting the big picture about pesticide use?  You know, all those nasty side effects on us and Mother Nature.

• "Caterpillars knocked from the tree or crawling on a patio may be killed by crushing. Use a broom to collect dead or crawling caterpillars around the home," advises one site.  So, a little housekeeping advice with the entomology lesson.

• Then there's what a neighbor of mine recently did: notice a tree without a single leaf remaining and wander around asking everyone how to kill the defoliators.  Too late, buddy.

ORGANIC EXTERMINATION
My own favorite technique (which I may even use someday) is the observant gardener taking action in early spring to poke holes in the tents to expose them to predators.  See the happy robins!

My second favorite isn't mentioned in the literature because - well, I don't know.  It's the old pick 'em off by hand and drop them into soapy water trick.  I instituted this extermination plan after discovering these roses completely defoliated, with the destruction moving quickly to neighboring roses.  A jar of soapy water is always on hand and the morning hunt is kinda fun.  (A form of hunting that even lefty animal-huggers can enjoy!)

This mano-a-mano, organic approach to insect control takes me back to the gardens of my childhood, where roses were routinely ravaged by Japanese beetles.  But beetle traps were hanging nearby and we just LOVED picking the beetles off by hand and dropping them in the traps. Or squashing them, of course - a highlight in any kid's day.

Just for fun, I Googled "Japanese beetle trap" and found this - one old-fashioned trap on the shelf with an arsenal of chemical warfare.  And the site?  It's called "Yardlover" but we know its target audience as yardeners.

Comments

[Jeff Gillman]

Nice post. You're exactly right about the extension service, of which I am a part. We love to tell people how to kill stuff with poisons, and generally people love us for it. Which isn't to say that we don't tell people to reduce pesticide use, because we do, but people seem to be happiest when we just tell them how to kill whatever ails them. And so we oblige. It's kind of sad really...

When I was a kid we had a blast taking burning sticks and lighting caterpillar tents on fire -- not something I'd ever recommend because of the obvious drawbacks of this technique -- but it was fun in a macabre sort of way.

[Amy Stewart]

They are truly horrifying. I generally use Bt if I can see the critters, or just cut out the offending tents and throw the whole thing in the trash if it's too much of a mess. I have also bought predatory Trichogramma wasps and released them into the garden; I have no idea if they stuck around, but I haven't had any tent caterpillars in a few years.

[El]

On Saturday we tried to give a whole nest of these things to our chickens, but they obviously emanate a "touche-pas" stink that our girls found completely unappetizing. So, soapy water it was.

And I *like* bugs, too. But let's be honest here: there're good bugs....

[Yolanda Elizabet]

Excellent post Susan although there's something missing. The first approach to combat those caterpillars should read:

- really smart gardeners emigrate to the Netherlands where they don't have those beasties. Problem solved! :-)

[Cheryl]

First of all, I have been a lurker until now, but I love your blog! So thank you.

I still have nightmares about the infestation-of-the-century of these furry little beasts in Central Florida. For weeks, I could not leave the house without getting them on me as they dropped down from the trees. I considered taking an extended vacation. If it ever happens again, I am purchasing a flame-thrower. I really must know how they are beneficial...like ticks and mosquitos?

[Ellis Hollow]

I remember people freaking out over gypsy moth caterpillars when I lived in Rhode Island circa 1980. I remember hearing about one poor soul who sprayed oven cleaner on their roses to try to stop them. Talk about destroying the village in order to save it. Hysterical. Literally. (Sorry firefly, couldn't resist.)

[Marte]

I remember a few years ago the northern Minnesota woods where we go fishing and camping was inundated with forest tent caterpillars. (Maybe a relative to the eastern?) They were everywhere -- huge writhing masses of them. They would fall off the trees onto anything we would try to cook on the campstove. It was the grossest thing I have ever seen but also very interesting.

[Ed Bruske]

Susan, we ran across a tent caterpillar infestation a few weeks ago visiting a friend in Virginia. "The Gardener's Guide to Pest Control," the textbook in our Organic Landscaping class at the USDA, gives the following recommendations as organic remedies for tent caterpillars:

Spraying with a bacillus thuringienis (BT) product when the caterpillars are still very small. This is a stomach poison and must be injested by the caterpillars.

Spraying or fogging with a growth regulator containing Diflubenzuron.

Spraying with a horticultural oil.

Spraying with an insecticidal soap.

Spraying with a protozoan insecticide.

[Ed Bruske]

Correction: That's "The Gardener's Guide to Common-Sense Pest Control."

[MaryContrary]

I grew up in a small town in those northern Minnesota woods, and the cyclical army worm (as we called them) infestations give a real insight into the notion of a plague of biblical proportions.

The plague was especially bad for a couple of years in my early teens and made me, frankly, crazy. Not amusing batty gardner crazy. I mean crazy crazy. I got absolutely unreasonably phobic about the things and just couldn't deal with them. I avoided going out of the house whenever possible and would only do my morning newspaper route with an umbrella to keep the things from falling on me out of the trees.

I'm over the bug phobia (and don't do much with the tent caterpillers other than punch holes in the webs if I get around to it), but I can still can summon a moment of real empathy for the Egyptians if I happen across the cheesetasticness of "The Ten Commandments" on television.

[Jodi DeLong]

Last year we were infested with a plague of White tussock moth caterpillars, which were also rampant throughout the woodlands, probably due to the mild winter previously. I actually bought a bottle of BtK to counteract them on my husband's young horsechestnut tree (his favourite plant in the world, given to him by me when we first moved here 8 years ago. It's going to flower this year and he's as excited as if we were expecting... thankfully we're not!) Normally I have a laissez-faire attitude to insects but these were defoliating all kinds of plants--and they were annoying.

Then I discovered we had monarch caterpillars again, and I ceased all hostilities, even though organic, and hoped the birds would take care of the tussock caterpillars. When they went to cocoons, I scraped them off where I could find them and dumped them into soapy water, then flushed down the loo to the septic system. There were also a lot of fall webworms around, and probably tent caterpillars earlier in the year. We had a colder winter this year so hopefully the boom will be followed by bust.

[Annie in Austin]

We don't have the volume of tent caterpillars that you talk about, but the webworms love pecan trees here in Austin.

Pecan trees are messy by nature, the flowers can trigger allergies and the squirrels get the harvest, so the shady green canopy is the main attraction. When the tent caterpillars destroy the leaves, even that value is gone.

We cut out any tents we can reach with pole pruners and ladders, we try to poke holes so that wasps can get in, but we don't spray BT, not wanting to kill off the butterfly larvae.

For other parts of the garden it's hand-to-hand combat. When I was young it couldn't do it, but time has given me the ability to squish pests, with certain kinds demanding gloves. Some harmful insects are washed off; some go into soapy water. Some are snipped with garden scissors.

While my actions are pretty calm and logical, Susan, my REactions are more visceral - just looking at the web full of squirming caterpillars clenches every muscle in the back of my neck and every instinct says, "Destroy!! Destroy!!" They are waaaayyy creepy!

Annie at the Transplantable Rose

[Beth]

Like Jeff, I'm also in Extension and everyone just wants to know what to spray. That's it. What magic spray? It's a little frustrating, but Jeff and I and hopefully other Extension personnel need to keep plugging some of the cutural/mechanical (poking with a stick, stomping, etc)controls that some people seem to have lost track of. Your boot will always work.

I love this blog, by the way. I get behind reading the posts, but I always try to catch up. Thanks.

[Julia]

Brava, Susan. I do just what you do--poke the nest with a stick and drag and scatter the worms and nest.
The birds will eat them. I've done this for the past 12 years (not that I've had them every year) and usually I don't even get them anymore. None this year which I hear is a bad one in this area. Stop overreacting, people ;)

[Eva]

I live in Wyoming and we have possibly 15 acres of sage which has been completely taken over by tent caterpillars. Going through and clipping off each one would take weeks, even if we went at it all day. I have no idea what stage they're in, but they've started wandering around outside of the cocoons now. Is it hopeless? (Please say no!)

[luise howell]

saw in a german newspaper last week that they are battling caterpillar infestations in their forest with vacuum systems and dressed in haz-mat suits.they also had a warning that the hairy caterpillars can agravate asthma sufferers and can cause bronchial problems.i guess they are more than just a little nuisance.

[sophia]

I love caterpillars! So, maybye there a bit af a nuisance, but hey stay away from the ones that cause damage and you'll be fine. But if you can't get away then that's just sad. Bye caterpillar haters, but hey, it's not my problem.

[Lanie]

I have literally thousands of these nasty creatures--and am completely overwhelmed by them. Not only are they crawling up the foundation of my house and eating my garden...they are lining the barks of my trees by the thousands. Help....I saw only one tent at a location too high to reach...yet there are literally thousands everywhere. I can only imagine that the population will grow faster and faster each year.

[Marty]

I live in McLure B.C. We have a campground actually. We have just found out that the Tussock Moth is here. I am a little worried as we have about 500 Douglas firs on our property and they are big and tall.....should I worry? What is the history on these things?