How many species live in your home?


This is a guest post from Matthew Holden, an applied mathematician based at the University of Queensland. I loved seeing his backyard biodiversity hunt on Twitter, because so many of his pictures were of invertebrates! His story…

Well that’s what I wanted to know about my home.

It all started one day, more than a year ago, when my housemate, Dr Andrew Rogers, was cleaning out his closet. He wanted to move the spiders outside and spare them from getting sucked up by our vacuum, during a much-needed cleaning session. But there was one problem, there were a lot of spiders, definitely several species. He thought, “How many spiders do I share the house with?” It was a slippery slope … it wasn’t long till we wanted to know all of the species in our home.

From then on, we regularly talked about conducting a very local biodiversity survey, but never got around to it. We were fortunate enough to even have a taxonomist, Dr Russell Yong, move in with us, who was keen to help out. But we kept putting it off.

Then the pandemic happened. We all decided to start working for home – a perfect time to do the survey. It would give us all a social activity to bond over during this time of isolation. Andrew even came up with a hashtag for us to share our findings #StayHomeBiodiversityChallenge.

I think we all guessed that there were likely at least 100 or so species in our house and yard, but we were shocked – as we surveyed each day, the tally kept rapidly increasing. We are now at 460 total species, with 409 animals and 51 plants. Of the 409 animals, 50 were vertebrates (mostly birds, but 6 mammals, 7 reptiles, and 2 frogs as well) and a whopping 359 invertebrates broken down below (316 of which were insects).

Moths 143
Flies 38
Bugs 31
Spiders 29
Butterflies 24
Beetles 21
Wasps 16
Ants 10
Bees 6
Lacewings/antlions 6
Grasshoppers/crickets/katydids 5
cockroaches 5
Mites 3
Dragonflies/damselflies 3
mantids 2
Snails 2
crustaceans 2
Centipedes 2
flatworms 1
earthworms 1
Nematodes 1
termites 1
Thrips 1
Webspinners 1
barklice 1
woodlice 1
millipedes 1
earwigs 1
alderflies 1

The results of the survey were quite shocking. 143 moths! What? That’s nuts. But it makes sense when you think about it. If your neighbourhood has grass in it, there are many moths whose caterpillars feed on the stuff. Then if you have any neighbours with fruiting trees, there are many fruit-piercing moths. Other moths like flower nectar, and there are even a few pesky moths that live in our pantries and closets. They are all attracted to light at night. So, if you want to see what moths you live with, just leave a light on your porch or balcony or in your yard. Or if you have none of those, leave a window open and keep the light on in that room. You will see many moths, and if you look closely, there will be several species. We also got a bit lucky with the timing. Most moths peak around March or so. So, we definitely benefited from adopting the “work from home” attitude early. We had a ton of moths during the first part of the survey. If we started now, we’d get much fewer, but we’d still probably see 50 or so species.

Sadly, we only had 21 beetles. Beetles make up the most diverse category of animal on the planet, and yet they are such a small part of our survey. While this year has been cold and dry, and our sampling methods my not favour beetles so much, we have to wonder where have all the beetles gone?

How we did the survey

Beside the surveys by our porch light, we regularly took a walk through all the vegetation around the house, paying special attention to the underside of leaves. While not looking under leaves, we were looking for movement. It’s easier to spot flying things if you are focussing of movement rather than looking for something that looks like an insect. Occasionally, we would shake a bush, and place a large container underneath, and go through what fell into the container. This was a good way to look for the insects on leaves that don’t fly much, or are weak fliers like beetles. We also spent some time under the house looking for, mostly, spiders.

We did several surveys where we grabbed some dirt and dead leaves from the ground and sorted through it for invertebrates. This yielded many tiny things that we could only ID to very broad categories. For example, there are many microscopic sized spiders in the soil. We were lucky enough to own an old microscope we bought for cheap off of gumtree a while back. But even then, it’s quite difficult to ID the microscopic organisms. The soil was also filled with small centipedes, millipedes, bark lice, worms, beetles, and much more.

Besides the old microscope, my most useful tool was my smartphone, armed with the iNaturalist app and a cheap macro-lens attachment for the phone’s camera. The iNaturalist app allows you to upload photos, and it will use image processing and machine learning to give suggestions about what the organism is. Experts on iNaturalist often refine or correct the guess. Or you can do it yourself by looking through a catalogue of species with iNaturalist records in your state/country. The macro-lens attachment was really helpful for IDing because it created photos with more details. My lens attachment does 7 times zoom without losing any pixel resolution and I purchased it off eBay for $20.

Even with the help of iNaturalist, and a taxonomist in the house, we knew it would be really tough to identify everything to species. So we agreed that we’d try our best to identify everything to as fine a taxonomic classification we could. But some things will always be too tough. For our numbers we counted “leaves” of the taxonomic tree of life. So if, for example, we couldn’t identify 3 insects to species, but one of them was in a family not previously observed in our sample, we’d count that as a new species. If the other two were in families that were already represented in our sample, we wouldn’t count them as new species until we were more certain what they were.

My life feels so much more enriched knowing all the species I live with. Plus, I now have a great idea for the perfect holiday gift for my family … a field guide to all of the wildlife in my home/yard! … scratch that, I think if they knew I lived with 400+ invertebrates they’d get the heebie jeebies and never visit ;). But happy that the hashtag has gotten many folks involved with their local wildlife around the world (from the USA to Germany, and of course at home in Oz).

© Matthew Holden 2020

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