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Invasion averted, but it gets weird: Spiders observed "petting" worms

A cool spring dampens FTC boom
A cool spring dampens FTC boom
by Ken Korczak

It appears an invasion has been avoided for another year. Hordes of forest tent caterpillars were expected to resurge and munch away millions of acres of tree foliage across northern Minnesota, but cool spring weather may have stemmed the tide.

Forest tent caterpillars (FTC) are commonly and erroneously called “armyworms,” but they are not the same species. Armyworms eat grasses and crops, such as oats, wheat, corn and barley, which is why they drive creepy crawly fear into the hearts of farmers.

But the forest tent caterpillar prefers to gormadize tree leaves. Their populations have a “boom or bust” dynamic. The Minnesota DNR had been expecting an explosion in caterpillar swarms this year -- but it looks now like 2015 will be the year.

In 2001 the ravenous crawlers deforested an incredible 7.5 million acres of hardwood forest, mostly across northeast Minnesota. They have a 10 to 16-year cycle. The first recorded Minnesota mass invasion was in 1891.


It’s not all bad, though. Forest tent caterpillars are a major source of lunch for a variety of birds, especially the nuthatch, which have been observed gorging themselves with juicy FTCs. Robins like them too as do frogs -- but even large species, including bears, consider the FTC a protein rich delicacy.

By the way, is the forest tent caterpillar fit for human consumption? The answer is yes!

A Missouri man, Paul Landkamer, reports that he has toasted and noshed the hairy FTC. He is what is known as an “entomophagist.” Entomophagy is the practice of eating bugs.

Landkamer has eaten dozens of different kinds of bugs over the years -- he even grinds them up and bakes them into cookies.He has sampled the forest tent caterpillar, but reports the hairy extending spines of the crawlers are difficult to swallow, even after "being toasted." READ MORE

In addition to hungry beasts and humans, the FTC has numerous enemies among the insect world, according to the imminent naturalist and educator, Dr. Clarence M. Weed, who published a fascinating monograph on the forest caterpillar in 1899.

In his publication, aptly titled, “The Forest Tent Caterpillar,” Dr. Weed offers a number of anecdotal notes, including this bizarre observation made his associate, whom he only identifies as “Miss Soule.”

Miss Soule spent endless hours observing the habits of the forest tent caterpillar and was surprised one day to find a group of about 20 harvester spiders (sometimes called daddy-long-legs) congregating on “a mat” of forest tent caterpillars.

The spiders were not eating the caterpillars, but simply hanging out with them -- and it gets even weirder.

Miss Soule reports:

“It seems this morning as if almost every larvae was attended by a (spider), which apparently stroked it with a leg or two or merely stood near or over it. Sometimes the touch made the larvae curl up, but more often it seemed to have no effect.”

Extremely odd!

Dr. Weed proclaimed to be baffled by the behavior of the spiders, and could only speculate that the daddy-long-legs “found food in connection with the caterpillars in some way.

Note: You can read Dr. Clarence M. Weed’s report on the forest tent caterpillar here: Google Books


As for the deforestation effects of the FTC, the harmful effect tends to be limited. Most trees regrow leaves lost to the caterpillar by mid-summer.

Once the forest tent caterpillar has eaten its fill, it makes a wispy white cocoon from which it will later emerge as a moth with pale tan wings. The wings bear a broad, brown stripe across the front.

The FTC moth is a night flier.

After mating, the female FTC moth will lay about 200 eggs which are covered with a tough bronze-colored resin casing. The eggs are extremely resilient inside this chamber -- studies show a less than 10 percent reduction in successful egg hatchings even after temperatures plunge to 40-below-zero or colder in Minnesota.

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