{"id":347,"date":"2025-08-11T08:38:30","date_gmt":"2025-08-11T15:38:30","guid":{"rendered":"https:\/\/scienceblog.com\/wildscience\/?p=347"},"modified":"2025-08-11T08:38:30","modified_gmt":"2025-08-11T15:38:30","slug":"hairy-caterpillars-swarm-every-decade-then-vanish","status":"publish","type":"post","link":"https:\/\/scienceblog.com\/wildscience\/2025\/08\/11\/hairy-caterpillars-swarm-every-decade-then-vanish\/","title":{"rendered":"Hairy Caterpillars Swarm Every Decade Then Vanish"},"content":{"rendered":"

Every decade or so, western tent caterpillars descend in hairy, squirming waves, covering trees, fences, and even houses, only to disappear almost overnight.<\/p>\n

A new study in the Journal of Animal Ecology<\/em> by University of British Columbia researchers, led by Dr. Judith Myers, draws on 50 years of field data to explain this striking boom-and-bust cycle. The research shows that viral disease and shifting reproduction rates are the twin engines driving population peaks and crashes, and that these native insects have proven surprisingly resistant to climate change.<\/p>\n

From Quiet Woods to Crawling Chaos<\/h2>\n

Western tent caterpillars (Malacosoma californicum pluviale<\/em>) are found from British Columbia to California, and east to Manitoba. Most years, they are all but invisible, quietly feeding on red alder and fruit tree leaves. But during outbreak years, their silky communal shelters appear everywhere, their numbers high enough to strip orchards bare. In 2012, a severe outbreak on Salt Spring Island even forced the cancellation of the annual apple festival.<\/p>\n

Eggs hatch in April, and larvae cluster in sunlit silken tents for warmth. By early June, they disperse to pupate, often clustering on vertical surfaces like walls or fenceposts. After one or two years of high densities, populations crash, leaving behind only a few scattered tents until the next build-up years later.<\/p>\n

The Science Behind the Swarms<\/h2>\n

Dr. Myers’ half-century of research, much of it in collaboration with Simon Fraser University’s Dr. Jenny Cory, reveals that two main factors shape the caterpillar cycle:<\/p>\n