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"Gall" on twig - not really a gall

This growth is not a gall, but rather a different part of an insect's life cycle.

Last week I received a photo from a county agent that showed a 'growth' on a poplar twig (see below).  The agent thought it was a gall, but as it turns out, this isn't a gall at all.  Instead, it's an egg mass from the forest tent caterpillar (Malacosoma disstria).  In this photo, the egg mass is on some type of poplar tree, likely a cottonwood.

Forest tent caterpillar, eggs, Chandra Langseth, 2017

Inside the mass are 150-200 individual eggs (see below), each one capable of producing another hungry caterpillar next year.  The egg masses are easily removed from the twigs, but they're hard to spot.  This one was removed from an apple tree.  Pulling them off and destroying them this year helps reduce the amount of insecticide that we'll apply next year.  That being said, forest tent caterpillar populations are cyclic and after peaking, they'll crash for several years and then slowly build up again.  (At our home, the last peak was in 2011 and densities were high 2017.  Looking forward to seeing if 2018 brings another massive outbreak, or a population crash.)

Forest tent caterpillar, eggs, Zeleznik

-Joe Zeleznik

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