Invisible aliens among us

A few weeks ago I attended a talk by Dr. Sarah Dudas at the Vancouver Island University (VIU). She was discussing the impact of shellfish farming on biodiversity. In one of her first slides, she put up four or six photographs of molluscs, and asked the audience which ones were native to British Columbia. It turned out that only one was. In fact, a significant number of marine organisms have been introduced accidentally in association with the introduction of the Japanese or Pacific oyster, Crassostrea gigas Thunberg, which

Japanese oyster. Attribution-NonCommercial-Bas Kers, ShareAlike 2.0 Generic (CC BY-NC-SA 2.0)

is the large, common oyster that is farmed, and is common along the southern BC coast. A good summary of the main species that have accompanied the introduction of the Japanese oyster, and their impact can be found at Exotic Introductions into BC Marine Waters: Major Trends. The Native or Olympia oyster, which was once widespread and common is now so rare that is has been blue listed under SARA. You can read more about the history and fate of the Olympia oyster at this blog from VIU’s Deep Bay Field Station.
Dr. Dudas’ talk made me think about what other exotic organisms are present among us, so I decided to write this blog. If we start looking around, we’ll find that many of the most common organisms we see around us are in fact introductions. Among arthropods, many familiar insects like earwigs (Dermaptera) are all introduced, with two of the four species

European earwig, Forficula auricularia

present in BC quite common. Most people are likely familiar with the European earwig, Forficula auricularia Linnaeus, which frequently appears in and around homes, and in coastal BC, the large seaside earwig, Anisolabis maritima (Bonelli) is commonly found under driftwood on sandy beaches. A number of ground beetles (Coleoptera: Carabidae) are commonly dominant in urban and suburban areas (Spence and Spence 1988). Most common is Pterostichus melanarius (Illiger), which seems to be present almost everywhere, and Carabus nemoralis O. F. Müller and C. granulatus Linnaeus are two fairly widespread and noticeable species because of their size. The most common (or at least most obvious) exotic around my home, and probably throughout southern BC at this point, is the European paper wasp, Polistes dominula (Christ), which seems to build its little nests pretty much wherever there is some

European paper wasp, Polistes dominula, resting on a mullein plant. Tappen, BC

protected space, e.g., bird and bat houses, mail boxes etc. To most people it is probably just seen as another yellowjacket wasp (Vespula and Dolichovespula spp.), but luckily it is much less aggressive than those pesky insects, so not quite as annoying to have around. Many common spiders are also introduced, e.g., the most common orb weaver in the area where I live is Araneus diadematus Clerck, as species I know well from my childhood. Indoors the so-called house spiders (Tegenaria and Eratigena spp) are also introduced. A more exotic looking introduction is the woodlouse spider, Dysdera crocata C. L. Koch, presumably introduced

The woodlouse spider, Dysdera crocata.

along with its primary prey, the sowbugs and pillbugs (See this blog for more information). Even our favourite garden helpers, the earthworms are almost exclusively exotic. Only four of 24 species are native, in fact (See this article for more information).
We don’t have to stop at invertebrates of course. Many common bird species are also introduced, e.g., the common starling, Sturnus vulgaris Linnaeus and the house sparrow, Passer domesticus (Linnaeus), which were early arrivals, and the more recent Eurasian collared dove, Streptopelia decaocto (Frivaldszky). The latter has marched across the North American continent in record time, and is now quite common in many areas in the west. Other groups are also on the move, e.g., a recent arrival on Vancouver Island is the European wall lizard, Podarcis muralis Garsault, which was apparently released on the Saanich peninsula about 50 years ago. It is now on the move having been spotted as far north as Denman Island, and one locale where it has been seen is within a km of my home in Nanaimo. If you see one, please inform Gavin Hanke ( at the Royal BC Museum, preferably along with a photo to ensure that it is not the native alligator lizard. A more familiar introduction to people in BC is the American bullfrog, Lithobates catesbeianus Shaw, which is now present pretty much everywhere in the lower mainland and on southern Vancouver Island.

American bullfrog, Lithobates catesbeianus

A very invisible problem is the introduction of non-native fish. Many of you may have heard of the snakehead (probably Ophiocephalus marmoratus Brind) spotted in a Burnaby pond, which led to an expensive hunt to remove the fish. Introductions by thoughtless individuals who release their pets occur with surprising frequency. Dragon Lake in Quesnel, BC, which is a primary source for rainbow trout stock, now has a thriving population of carp Carassius auratus (Linnaeus), after someone released their goldfish (a domesticated form of the wild carp) into the lake. Smallmouth bass (Micropterus dolomieu
Lacépède), northern pike (Esox lucius Linnaeus), and various bait fish have led to a number of expensive actions in order to restore the system to health. The latest example is what is thought to have been deliberate introductions of yellow perch, Perca flavescens Mitchill, in two Okanagan lakes.
This was written pretty much off the top of my head. In spite of that I could go on, indicating that exotic organisms are rather more common than we might like, the fact is that we are essentially surrounded by aliens, and unfortunately many of them are displacing our native fauna. Many of the exotics appear to be harmless, but to native fauna, the presence of these intruders could be disastrous. The take-home message is: do not release anything that does not belong here. We have plenty of our own species to enjoy!

Most of the information available on the internet relates to invasive “pests”, i.e., those species that cause direct damage to resources of interest to humans. Nevertheless, even a relatively minor effort searching the internet would likely give you a good impression of the extent of this problem. My intent with this blog was simply to plant the seed!

Spence, J.R. and Spence, D.H. 1988. ‘Of ground-beetles and men: introduced species and the synanthropic fauna of Western Canada’, Memoirs of the Entomological Society of Canada, 120(S144): 151–168. doi: 10.4039/entm120144151-1.