“The question is not what you look at, but what you see.”
Henry David Thoreau
For as long as I can remember, insects, spiders and other arthropods have fascinated me.
Some of my earliest memories include watching huge European fishing spiders (Dolomedes fimbriatus) at a dock on a lake where my uncle had a cabin. Many years later I kept house spiders (Agelenidae) that I found in the basement of our apartment building in jars in my bedroom. I was fortunate to be able to turn this childhood fascination into a career.
In the first installment of this blog topic, I discussed vertebrates in our backyard in south Nanaimo. It is the invertebrates that really dominate in terms of diversity, however, and in this part I will focus on non-insect invertebrates. No matter how often you are out there looking, there are always new discoveries waiting for you. I have never been much of a collector, and in my old age I have developed an aversion to killing living even the tiniest of creatures, so I often cannot identify what I find. The emergence of iNaturalist has vastly improved the odds of identifying plants and animals, even if it often is only possible to Order, Family or Genus.
So what is out there? There are earth worms of course – most of these are actually invasive as most native species went extinct during the last ice age. See the eFauna checklist for specifics. If you look under pieces of wood, rocks and other moisture-retaining features, you will find a variety of organisms that require a moist environment
to survive. Sowbugs and pillbugs, which are Crustaceans, i.e., they are related to crabs and shrimp, are very common. Two sowbug species, the European Sowbug (Oniscus asellus), and the Common Rough Woodlouse (Porcellio scaber), are particularly common under any piece of wood (hence one of the other many names, wood louse), and the Common Pill-bug (Armadillidium vulgare), is also relatively common. The latter rolls up into a ball like an armadillo when disturbed, which explains the generic name. All three are introduced. They have evolved behavioural, morphological and physiological adaptations for life out of water, with some groups having evolved several types of primitive lungs. Several species of centipede (Chilopoda) and millipede (Diplopoda) can also be found under rocks and pieces of wood, although one occasional visitor, the Yellow-spotted or Cyanide Millipede (Harpaphe haydeniana) can often be seen in the open. The name refers to defensive secretions, which are advertised by the millipede with its contrasting black and yellow aposematic (=warning) colours. Centipedes are predatory whereas millipedes are scavengers. They are quite easily separated as millipedes have two pairs of leg per segment (Greek diplos = double) whereas centipedes have one pair. The common names refer to their numerous legs, although neither lives up to the count indicated (100 and 1000, respectively). Together they make up the Subphylum Myriapoda.
Similar to the isopods, snails and slugs, the Pulmonates (Latin Pulmo = lung), which comprise a subgroup (previously a Subclass or Order) of the mollusk Class Gastropoda, are much too common. The name refers to the primitive “lung” they possess to enable them to live in a terrestrial environment. If you look carefully on a live slug or snail, you will see a small opening on the right side. This is the pneumostome (Greek pneumo = lung stóma = mouth ), through which air is drawn into the highly vascularized mantle cavity. In terms of species, introduced Grove snails (Cepaea nemoralis) vary from a plain brown
shell to a pretty cream with or without dark stripes. Most striking among the slugs are the massive Pacific Banana slugs (Ariolimax columbianus), as well as large slugs in the Arion ater group, which are introduced. These giants can make quick work of plants, so they are usually unceremoniously moved into the field behind our yard.
The arachnid fauna, which has always fascinated me, is very diverse. Among my favourite group, the jumping spiders (Family Salticidae), I have found 4-5 species, the
most common of which are the Zebra jumping spider (Salticus scenicus) and the Flat California jumper, Platycryptus californicus. The latter finds its way into the house with amazing regularity, and I generally leave them or gently move them outdoors. Jumping spiders have numerous characteristics that make them worthy of your attention. They are highly visual, some have shown astounding intelligence for such diminutive creatures, and their courting rituals are both fascinating and entertaining (I highly recommend a google search for ‘peacock spider’ videos by Jürgen Otto). Males in particular sometimes sport some pretty gaudy colours to charm the females, an evolutionary parallel to male birds. Wolf spiders (Family Lycosidae) are ever-present roaming hunters most often seen as they bask in the sun, scurrying into hiding at the slightest disturbance. Like the jumping spiders, they are highly visual, albeit not possessing the visual acuity of salticids. In the summer you may spot females carrying an egg sac around with them, and once the spiderlings emerge, she will let them hitchhike on her abdomen for a short period. This may surprise you, but in fact many types of spiders are very good mothers – the males do not contribute at all after mating, if they even survive that adventure!
The giant house spider, Eratigena atrica, a much less charming and somewhat scary-looking but harmless member of the Family Agelenidae, is another semi-frequent house guest. Females generally stay in their funnel webs, which they build in protected areas, so it is the males that make unwelcome appearances at times. The garage is home to numerous Cellar spiders (Pholcus phalangiodes), which are true spiders in the family Pholcidae, unlike the Harvestman ‘spiders’. False black widows, Steatoda grossa, which share the Family Theridiidae with its more famous Latrodectus species relatives, are generally making their homes in garages or basements. Like the black widows, false widows make tanglefoot webs that are ideal for ensnaring hapless passersby like ants, other spiders, or isopods.
Moving back outdoors, there is no end to the diversity. In the fall, orb web spiders in the family Aranaeidae become extremely common. The specimens we see most often are females, which with their more or less colourful swollen abdomens look more imposing
than they really are. As with many creatures around human habitation, it is an introduced species, the Cross spider, Araneus diadematus, that is the most common species on southern Vancouver Island. Another common (but rarely seen) introduction is the Woodlouse hunter, Dysdera crocata (Family Dysderidae), which sports massive (relative to the size of the spider) fang-armed chelicerae (jaws). This species can be encountered under wood or buried in loose soil, and as the name implies, it specializes on wood lice. Looking a little further up, specifically on flowers, you may find the common Goldenrod spider (Misumena vatia), a sit-and-wait predator that is a member of
the crab spider family (Thomisidae). They have some limited ability to change colour to match the flower they are on. This species catches pollinators and other flower visitors, but the impact is not significant enough to cause any harm. While doing some clearing
up, I recently found a crab spider species I had not seen before, the Brown-legged Crab Spider (Coriarachne brunneipes). This very flat species is associated with wood, where it waits for potential prey. Shortly after I found this species, I also found a female Pacific Foldingdoor Spider (Antrodiaetus pacificus), one of the few mygalomorph spider species we have, which means it is related to tarantulas. They are characterized by fangs that move vertically. All other spiders are araneomorph with fangs that move laterally. The Pacific Foldingdoor spider builds burrows in soft soil or wood. During the day the entrance is covered with a silk door, but at night it is opened and the spider sits at the entrance waiting to rush out at passing beetles or other prey. Having poor eye-sight, it is alerted to the presence of prey by silk threads extending out from the burrow.
When you are small, staying alive is of course a priority. Several families of spider use the strategy of mimicry. Do you see an ant? Look closer, sometimes it may be a spider. Common around our place is one of the ground spiders (Family Gnaphosidae) in the
genus Sergiolus (most likely S. columbianus). Some tropical species can be very ant-like, whereas most of our species tend to be less sophisticated.
There are lots of other groups of spiders, of course. In fact, spiders are some of the most abundant organisms on earth. It is said that you are never more than a meter or so from a spider. Fortunately for arachnophobes, they keep themselves to themselves most of the time, and they are completely harmless in spite of the frequent reports of spider bites, which are mostly caused by something else, but at best blamed on some innocent spider that happened to be nearby, and at worst just assumed (Bennett and Vetter 2004; Vetter and Isbister 2008). The largest group, the sheet-web spiders, Family Linyphiidae, were called money spiders in the UK because they were thought to bring good luck. These are generally tiny spiders that can occur in huge numbers. There small webs are often visible in grassy fields during the fall, when dew reveals their presence. The males in the Subfamily Erigoninae, can sport bizarre shapes on the prosoma (front part), including turrets for their eyes. My point is that spiders deserve some respect. If you get to know them, you may even learn to like them!
Bennett, R.G., and R. S. Vetter. 2004. An approach to spider bites. Erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada. Canadian Family Physician 50: 1098–1101.
Vetter R.S., and G.K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology. 53: 409-29.