Malacosoma sp. “Tent Moth” Lasiocampidae, pupa on
Larix occidentalis “Western Larch” Pinaceae

Apgar Lookout Trail, Glacier National Park, MT
October 9, 2015
Robert Niese

The trails around Apgar are rife with Lasiocampidae pupae. They’ve spun their webby cocoons in every manner of tree, shrub, and man-made structure. Around Missoula, it wasn’t a very big year for tent moth caterpillars, but only a hundred miles away in Glacier National Park, Malacosoma numbers were significantly higher. These species go through regular boom and bust cycles and some years they become so abundant that entire forests can get defoliated. In my search of the literature, it appears that these moths overwinter as eggs, not as pupae. These pupating individuals certainly won’t survive the oncoming cold if that is indeed the case.

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Malacosoma californica “Western Tent Caterpillar Moth” Lasiocampidae

Clinton, MT
July 25, 2015
Robert Niese

Tent caterpillar moths were some of our most abundant visitors during our Mothlighting event for National Moth Week with the Missoula Butterfly House. They are positively adorable as adults, wouldn’t you agree? In our area, we tend to have mostly Western Tent Caterpillars, but we do also get Forest Tent Caterpillars (M. disstria). Caterpillars of M. disstria tend to have broader blue dorsal bands, keyhole-shaped white dorsal spots, and whiter tufts of lateral hairs than M. californica, which, in our area, tend to have more yellow than blue

(however, farther east they tend to lack yellow entirely)

and tend to have dash-shaped white dorsal spots. Adults are far more difficult to distinguish, but in general, M. californica tends to have two lighter-colored lateral bands on its forewings in addition to dark bands, while M disstria tends to lack these bands and only has dark bands. But from the underside, they all just look like teddy bears.

Malacosoma californica “Western Tent Caterpillar” Lasiocampidae

Drinking Horse Mountain, Bozeman, MT
June 3, 2015
Robert Niese

Normally, tent caterpillars live in large groups in the safety of their silk “tents,” but this individual appears to have wandered off on its own. Often, after defoliating all the foliage on their first tent-plant, caterpillars will seek out food on nearby trees. But this individual looks really big and I suspect that it is seeking some quiet place to metamorphose into an adult moth. Learn more about these awesome moths here.

Happy National Moth Week!

Malacosoma californica “Western Tent Caterpillar” Lasiocampidae

Great Burn, Lolo National Forest, MT
July 10, 2015
Robert Niese

Tent caterpillars are really fascinating critters! In some years, populations of tent caterpillars explode and entire forests can be defoliated by these voracious animals. Fortunately, this extensive herbivory does will not kill most trees, although some eastern forests have experienced large-scale tree deaths when tent caterpillar outbreaks coincided with drought. This year, tent caterpillars have been in relatively low numbers. Learn more about these awesome moths here!

Happy National Moth Week!