A little life lesson and a plea for perspective

A little life lesson and a plea for perspective

When I walk through the forest, along a beach, or even if I simply sit on the grass in the backyard, there’s something I frequently consider that I’m guessing many of you rarely do: how many animals have I accidentally killed in the process? The reality is that our individual actions, especially if they are outdoorsy things like hiking cross-country, strolling along beaches, exploring parks, or even just plain old picnicking, likely result in the demise of dozens, hundreds, or even, potentially, thousands of individual animals. Each day. This is where your everyday actions meet real invertebrate biodiversity. It’s worth bearing in mind, not because there is much we can realistically do about this, but because there’s a lesson here about just how ubiquitous terrestrial invertebrate life is.

Now, for perspective, we’re talking here about little things. Not only the little things you might be familiar with – macro-invertebrates like snails and butterflies, beetles and bugs, spiders, ants and flies – but really little things: what we might call ‘micro-arthropods’ and other small non-arthropod invertebrates. These organisms, which include animals like springtails, mites, pauropods, symphylans, nematodes and a wide array of other little invertebrates, make up the majority of terrestrial animals on the planet. The numbers we’re talking about are almost unimaginable. Sit down in the forest, or in your backyard, and there will almost certainly be at least a thousand of these little creatures under your bum-print, on the vegetation, in the leaf litter and in the soil beneath. Indeed, many studies have shown that there are usually several tens of thousands – of both mites and springtails representing dozens to hundreds of species – per square metre of forest habitat in temperate regions across the planet. Assuming a minimum of 10,000 each per square metre, that’s more than 200 million of these little animals per hectare! Even pasture and gardens can have similar numbers, but usually of fewer species.

A selection of micro-arthropods. Row 1: Symphyla; Pauropoda; Diplura. 2. Mites: Bdellidae; Erythraeidae; Eriorhynchidae. 3. Mites: Oribatid; Linopodidae; Oribatid. 4. Springtails: Cassagnella; Australonura; Dicyrtomina. Images: Nick Porch

So why do I think about my accidental impact on these little beasts? Firstly, it’s because I find these little things fascinating and, secondly, it’s because I also collect and kill arthropod specimens for research. I’ve never specifically quantified how many specimens (and of how many insect species) I might collect in a year. It would be highly variable depending on the projects I’m working on and whether I’m using passive (trapping) or active (hand collecting) collecting approaches. There’s little doubt that in some years it would be several thousand specimens of hundreds of species. Most of these species are poorly known, many represent undescribed species, and some are the first ever collection of a previously unknown species or even occasionally, genus. Many are from places where entomologists rarely visit. Without these collections, some of these species may have never been discovered, never be formally described, and could have become silently extinct without anyone knowing. That’s more than a little sad.

Collecting for science, especially (but not only) insects and other invertebrates, is essential to developing a comprehensive understanding of the evolution, diversity and conservation of our biota. Most small invertebrates ­- and most invertebrates are small – cannot be reliably recognised in the field or even from high quality images (especially not from more easily obtainable poor quality images). There are of course exceptions – like butterflies and dragonflies – but these mostly belong to the larger and more conspicuous groups of invertebrates. Getting high quality images of live specimens of most biodiversity is nigh on impossible anyway, especially when the reality is that when you decide that you’re going to get a picture of species X, you’ll find out that species X was last seen in 1932, and only once prior to that. Most likely species X will next be seen again in a trap sample (or is it really species X or something new and related?). Perhaps there’s no-one around with the expertise to identify which species it is, anyway. Archived in museums, specimens form the basis for future revision and enhanced understanding. We begin to understand biodiversity and our changing planet based on these archived specimens: where they occurred, how their distribution has changed through time and will likely change into the future, their evolutionary relationships, and origins. Death, in this case, is future understanding.

When discussing this issue with students, there are always some who question the need to take what really are relatively small numbers of specimens for scientific study. In this context I’ve usually asked them several questions regarding their understanding of human impact on invertebrate diversity. Perspective is important. If they can’t be convinced that there are good scientific reasons for taking specimens, I ask them how they got to university that day. Most respond they drove. If they’re open-minded and willing, I’ll ask them to show me their car – insects smeared, smushed and smashed all over it, more in summer, less in winter. Cars kill billions of insects and other invertebrates every day. I’m sure you’ve noticed crashing into hundreds of insects as you drive, especially on warm summer evenings. You’ve only noticed the big ones and may not have recognised the micro-impacts that represent small ones. Tens of thousands of species of insect fly and are potential road-kill; have you ever considered how many insects you kill for every kilometre spent on the road? Everyday life results in death.

Macroinvertebrates. Row 1: Nitidulidae (Sap beetle) with a fly larva; Psocoptera (Psocid); Psychodidae (Drain fly). 2. Camponotus (Ant); Isopoda (Slater); Miridae (True bug). 3. Holoplatys (Spider); Hymenoptera (Wasp); Helicarion (Snail). 4.Vanessa (Butterfly); Psuedoscorpion; Phlaeothripidae (Thrips). Images: Nick Porch

Secondly, if they didn’t drive I’ll ask them if they enjoy outdoor pursuits, like walking. Almost no one considers that walking is detrimental to terrestrial invertebrates, in some contexts resulting in the death of animals with every step. Logically, it makes sense that it does given the numbers mentioned above, yet I didn’t really consider the potential magnitude of the matter until a spring day spent in Cranbourne Botanical Gardens, last year. I noticed beetle larvae were out and about and in high abundances, which meant they were crawling across walking paths. The paths had mostly been swept clean by rain the day before and yet they were littered with little corpses: I counted over 200 dead and dying beetle larva in around 25 metres of path. Not only were there beetle larva, but when wriggling along a path on my tummy the carnage became more obvious, with a wide range of other dead and dying invertebrates; ants dominating, but including spiders, amphipods, adult beetles of six species, and dozens of caterpillar larvae. Even on my tummy with my eyes close to the ground, it would have been hard to have seen the superabundant micro-arthropods that would have also been impacted. Should we ban walking?

You may have guessed my point by now. Terrestrial invertebrates are so incredibly abundant and ubiquitous that you can’t possibly go about your business in the outdoors without inadvertently killing dozens (in some cases 100s, or even sometimes 1000s). Every day. 100s. 1000s if you like to take long walks along forest paths or drive a distance on warm spring or summer evenings. Potentially more if you walk off-path like most passionate nature lovers like to. The reality is that this is just life. The specimens taken for research represent a miniscule proportion of the everyday human impact on invertebrate biodiversity. So, although we can’t go through life without touching the ground, we certainly can endeavour to more frequently look down, and consider the wonderful diversity and ubiquity of the little things.

Banner image of a Talaurinus weevil courtesy of Nick Porch.

Nick Porch

Nick Porch is Senior Lecturer in Environmental Earth Science at Deakin University. His passion is terrestrial invertebrates - especially beetles - and the recent fossil record of human impact on Indo-Pacific island biodiversity.

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