Park staff in the Victoria area are on the lookout for an innocuous looking off-white mushroom as they mow municipal boulevards because of a bumper crop of deadly death caps that started popping up in July.

A year ago, the mushroom — blamed for 90 per cent of fatal mushroom poisoning on the planet — killed a three-year-old boy in Victoria after he ingested the fungus his family foraged near a sidewalk, not realizing the danger.

This was the first documented death in B.C. from the mushroom, an invasive species first officially reported in 1997. Officials believe it came along with imported ornamental trees half a century ago.

This year, despite a dry summer, mushroom experts say death caps are thriving  — especially if well watered.

"The populations were high. We felt that we needed to do something," said Chris Hyde-Lay, manager of Oak Bay parks services, which maintains 27 kilometres of public space.

"So the crews have been picking them, and to date we've picked well over 1,000 mushrooms just off our boulevards."

But parks staff can't touch private lawns, where mushrooms often sprout.

Bucket of death caps

A bucket of some of the 1,000 death cap mushrooms picked off Oak Bay municipal boulevards since July 2017. (Oak Bay Parks staff)

Death cap adapted

The non-native species, which is usually associated with mature deciduous European hardwood trees such as Linden, English oak, chestnut and hornbeam, has now adapted to grow with a local host.

"Unfortunately the fungus has now learned how to grow with the roots of our native Garry Oak," said Andy MacKinnon, a biologist and forest ecologist in Metchosin with an expertise in mushroom identification.

So now that the deadly mushroom can use a native species as a host it could sprout up kilometres away. Before, mycologists knew exactly where to find the ornamental trees that acted as hosts.

The so-called death cap mushroom — or Amanita phalloide — is rife with toxins that attack the liver, kidney and other organs. The poison causes nausea, vomiting, low blood pressure, dizziness, and liver and kidney failure.

Poster death cap

Mushroom experts and health authorities have created a poster to try to warn people in many languages to beware of the danger of so-called death cap mushrooms. (Island Health, UBC, the Wall Foundation and local mycologists)

There have been two human poisonings reported in B.C.

In 2003 an Oak Bay man survived after cooking and eating the mushrooms thinking they were puffballs. And last year a toddler died after ingesting the fungi. 

Life cycle of the death cap

The death cap mushroom starts as button-shaped bulb and opens into a flat-capped mushroom that turns darker brown-green as it matures. (Natural Resources Canada/Canadian Forest Service)

After that, health authorities, the University of British Columbia and local mycologists produced a poster to warn people what to look for before eating mushrooms.

There are edible species — such a so-called straw mushrooms — which grow in other countries and look similar.

Death caps start as a small button-like dome that's mostly white. They flatten out and change colour to a darker greenish brown or yellowed cap as they mature.

They have a distinct cup at the base of the stem underground and a frill or skirt below the cap.

Death caps usually appear in early fall — but arrived in late summer this year.

"You don't normally see them until this time of year — when nature starts watering," said Brenda Callan, a mycologist with the Canadian Forest Service.

But local gardening practices that include more frequent watering are making a haven for the infamous mushroom.

Death Caps

Death caps mature and take on a brassy-green colour. The non-native fungus thrives at the base of certain trees, and has now adapted to use the local Garry Oak as a host. (Natural Resources Canada/Canadian Forest Service)