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These caterpillars bug people out of all proportion to the damage they do. They live in colonies, feeding freely by day throughout a tree (most often, fruit trees including crabapples and ornamental cherries). At night and on very gray days they gather in a communal web in a branch crotch.
When their numbers are high, they can defoliate a tree but even so, the tree is almost never permanently injured. Not, that is, until the gardener comes out with a flamethrower of some kind to burn out the tents.
Who ever came up with that idea?! Think about it: Here are caterpillars doing nothing more than noshing on ephemeral parts of the tree, parts which only last the year. They don't hurt the wood or the buds. If the plant loses enough foliage that it is tweaked to produce more that same year, the caterpillars will have finished and departed by the time it emerges.
And to get rid of them we burn the wood the tree took years to produce?
1) Get 'em before they hatch, before they do any damage. All it takes is a bit of phenology, details of which are provided to us as part of the lifework of Don Orton of the Morton Arboretum in his book Coincide. We know that just as the saucer magnolia buds are most pink and some are opening, these caterpillars hatch out of the egg masses the moths laid last fall on twigs, in crotches of the target trees.
The egg masses are easy to see (below) if you know to look for them. They can be scraped off with a thumbnail. No fire or chemicals required. Ground dwelling predators and fungi will snarf up those eggs as soon as they fall.
The eggs in this mass have already enclosed - hatched. You can see (below, right) that the individual cells are empty.
We know about many insect emergence times as they relate to various plants' development because age old wisdom plus a lifetime of new observations have been compiled by Don Orton in a very well respected reference.
2) Go out in the evening when they are all in that tent and yoink them out of the tree. Throw them to the birds. Okay, maybe you're more squeamish than our friend Cotton Harrison of Mary's Plant Farm was, in which case you should wear gloves.
3) Look the other way. The damage is not
life threatening and the birds need insects
to eat. Besides, you have lots of better
things to do, right?
We'd love to spend more time cross referencing the pieces of this library. What comes to mind here are other tent making caterpillars sometimes confused with tent caterpillar. It would take just a little while to find and link to or post those photos! We can do that with the aid of individual Sponsorships by those our writing has helped.
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