2 New Invasive Species Documented in Vancouver This August!

What comes to mind when you think of British Columbia? Maybe the crystal clear lakes or the lush temperate coniferous forests? Well when I went to Vancouver last month, I was constantly on the lookout for secretive invasive species that were hidden just a couple minutes away from the sprawling metropolis.

While thousands of invasive species are present throughout Vancouver and British Columbia as a whole, I was focused on finding and document small and/or relatively new populations. I used the citizen-science platform iNaturalist as a starting point to track down invasive species. This method was highly successful. The "map" feature on iNaturalist involves a 2d map with red dots, with each dot representing an observation of a species. Any observations that are far away from a documented population could suggest either an erroneous location or more importantly, a new population.

1. Nosy Pill Woodlouse (Armadillidium nasatum).

Originally from Europe, this species was introduced to the Eastern North America centuries ago via ships and colonists. Over the last 100 years, this species has exploded in population and is now abundant from Nova Scotia to Georgia. Despite their profusion on the East Coast, they are seldom seen on the West Coast. This is likely due to the specific habitat needs of A. nasatum, and competition with other highly adaptive European species. A rostrum-like structure in-between the eyes of A. nasatum prevents it from rolling up into a full ball. Because of this, the species cannot roll up into a complete ball, making it unable to gain moisture and thus survive in California's arid climates. In addition, other European species like A. vulgare, Porcellio scaber/dilatus and Porcellionides have been established for longer amounts of time, making it harder for A. nasatum to establish due to completion.

However, it's not surprising an isolated part of the Living Wall next to the Olympic Cauldron in Vancouver is home to a small but dense population of these isopods. While I was browsing the citizen-science platform iNaturalist, I came across a singular observation of A. nasatum from that area, near the waterfront. However, the accuracy bubble for the location covered the entire city, making it less likely that the specimen could be found at that exact spot. The photos showed multiple specimens feeding on a concrete surface, suggesting that there may be an established population in the area rather than just a single individual.

I went to that oceanfront location the next day to look for the isopods. The habitat consisted of a modern-looking slanted roof, with an assortment of planted non-native ornamental grasses. I looked on the concrete ledge near the grasses and sure enough I spotted at least five isopods. As I walked up the path near the waterfront I saw more and more isopods. Interestingly, other species of isopods that were well established in the rest of the city (Oniscus ascellus, Philoscia muscorum and A. vulgare) were absent from the area, suggesting that A. nasatum has marked it's dominance in this locale. I left the living wall where the population's stronghold was and walked around the corner to an urban meadow with mulch and scattered weeds. No isopods were seen.

After I left I thought deeply about what made this habitat so favorable for this uncommon species. They might have introduced here via the ornamental grasses, or other human materials. The fact that no other isopod species were found suggests that the specimens were introduced alone, giving them plenty of time to establish. The coastal environment makes the temperatures more neutral and the climate more humid, which are the exact conditions that A. nasatum favors.

2. Common wall lizard (Podarcis muralis)

The common wall lizard is smaller lizard that is native to Europe. It's body frame is slender, with a longer tail, a narrow head and stubby legs. Despite it's skinny frame, it is a comparatively agile lizard, which responds quickly to sudden movements with irregular jerky strides. They enjoy hanging out near human-made habitats such as outdoor stone walls (hence their name)

The lizard's color is quite striking. Although their color morphs vary quite significantly within subspecies in their native Balkan habitats, the specimens in Canada typically have a base color of brown, grey, or olive-green, often including intricate networks of dark spots, streaks, or reticulated patterns along the back and flanks.

Perhaps you've heard of the invasive Podarcis muralis in the nearby Canadian town of Victoria? Unlike the Nosy Pill Woodlouse, we know exactly when and how the specimens arrived. In the late 60s or early 70s, a pet shop in Saanich closed, and the owner released some 10-20 lizards into the wild. The population exploded significantly since then - now reaching about 1 lizard for every 1.7 to 1.9 square meters in optimal conditions!

In Saanich and Victoria, several species of native reptiles face a major threat from Podacis muralis. Elgaria coerulea spp. principis (Northwestern Alligator Lizard), a similar-looking native lizard and Contia tenuis (Common Sharp Tailed Snake) have already been pushed out of residential areas and are now restricted to undisturbed forests.

Despite their density in Vancouver Island, they have not been as prevalent in Vancouver proper. This is likely because Victoria and Vancouver are separated by the Strait of Georgia (body of water). Accidental oversea transportation for larger vertebrates like lizards are much more difficult than smaller creatures like isopods.

However, I went on iNaturalist to try to locate a population. Sure enough, there were a couple stray observations of P. muralis from Surrey, a smaller city forty minutes east of Vancouver. Several of the commenters on iNaturalist expressed concern, as there has not really been any published proof of this population, and it seemed to be growing rapidly.

When I traveled to the suburban neighborhood, I tried to be stealth, as the lizards are quick and blend in to the greenery. As I leaned over in someone's front yard, I spotted a spindle of green dart into the bush. I got my camera out waited for the juvenile P. muralis to emerge again. When it did, I took these three lousy shots (of three different individuals):

Obviously this one above is the clearest picture. Although it is still not the best shot I could have taken of the lizard, it is a clear enough example of a juvenile Podarcis muralis. As you can see the perivertebral stripe is a constant olive green, followed by light yellow and black dorsolateral stripes. The green perivertebral will fade with age and become more reticulated, with black or yellow spots.

Seeing introduced species thrive outside their native habitats made me ponder about how they got there, how they are effecting the local environment, or what allows them to be so successful.