Bagworms have been spotted in Hamilton. Here’s what to do if you find the insects or their pine cone-shaped sacs

These adaptive insects spin cocoons suspended from tree branches, using material from the host tree to create a camouflaged, pine cone appearance.

Bagworm larvae can attack both coniferous and deciduous trees. Common evergreen hosts include hemlock, cedar, juniper, pine and spruce. The young larvae are black and shiny on top with a dull amber underside. As adults, the males develop into flying moths, while the wingless females remain hidden inside the pouch.

Marc Rhainds, a research scientist with the Canadian Forestry Service, said bagworms aren’t native to Ontario, but have expanded their range from the Northern U.S. into southern Ontario in recent years.

He first encountered the insects in Windsor in 2009.

Rhainds noted the larvae prefer arborvitae, cedars, white pine and blue spruce, but will devour a wide range of vegetation. As they gorge themselves on plant matter, the larvae grow larger, taking on a maggot-like appearance.

“There’s about 1,000 species of bagworms and what makes them remarkable is it’s the only group of Lepidoptera (the order of insects that includes butterflies and moths) where the females have no wings,” said Rhainds.

While extreme temperatures can freeze and kill the bagworm eggs, Rhainds noted, “that was a winter where the eggs would not have died.”

Rhainds said bagworms enjoy the sun.

“They’re not the typical forestry pest in the sense that they don’t do very well when it’s wet. If the bag gets wet, you can have mould growing inside. They are creatures of the sun.”

Davey Tree Company notes in a blog post that while you probably won’t see the bagworms themselves, the insects are more commonly identified by their baglike cocoons, measuring about five centimetres long. Each bag can hold up to 1,000 eggs that hatch in the late spring or early summer.

In their larval stage, the bagworms are barely larger than a pinhead. The caterpillars use a silk thread as a parachute to travel to nearby trees.

Chris Deathe, district manager of Davey Tree Company’s Hamilton office, encountered bagworms locally for the first time last year at two residential properties.

Both detections involved Mountbatten junipers. Physical removal of the egg sacs was the only action needed in both cases.

Deathe has yet to find any serious infestations in the Hamilton area, but noted landscapers may discover bagworm sacs when trimming junipers and cedars.

“It’s not (time to) hit the panic button right now,” said Deathe. “It’s not here yet, at that level.”

Junipers impacted by bagworms will have a rusted, or bronzelike appearance, Deathe added.

If homeowners spot one or two bagworm cocoons on a tree, Deathe said removing them is likely all that’s needed.

Kaitlyn Fleming, assistant professor at Trent School of the Environment, said bagworms pose a lesser threat than invasive pests like Lymantria dispar dispar (LDD) moths and the emerald ash borer.

“The trees probably do have some resistance to them,” she added.

Fleming also said that while bagworms can be treated with insecticide, the most effective abatement is removing the cocoon from the tree before the eggs hatch in May or June and submerging it in soapy water. Once that’s done, seal the cocoon in plastic and dispose of it in the trash.