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Sunday Spinelessness – The sight of a wild slug eating David Winter Apr 17

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Did you know that I’m in the pocket of big bussiness ? Or that I set out to bamboozle people with fancy graphs? Or that I show the typical arrogance of the modern scientist? Well, it was news to me as well, but all this, and much more, appeared in the comments underneath my article on Ken Ring’s (non)ability to predict earthquakes when it was picked up by the National Business Review. One of my crtics did a little research about me and decided that… well I’m not sure what he decided:

As for people like David Winter – well he is in the pocket of people like the NBR – after all if the economy goes down the gurgler he just might not get any more freebee grants so he can go off and study snail trails. Studying snail trails wouldn’t engage someone for many hours a day, no doubt why he has had time to pen the “syndicated” article above. So here we have people like David Winter and the NBR “feeding” of the Christchurch earthquake.

I’ve had plenty of support, both public and private, in funding my research and I’m very grateful for it, but I’m not sure propping up a right-wing newspaper would be a very good way to expand spending on basic research. As it happens, I have never studied snail trails (although there’s plenty of science in that mucous), but I’ve looked into something I’m sure my anonymous critic would be equally dismissive of.

I want to know what my snails eat. That might seem like an easy question to answer, couldn’t I just set up in the field with a notebook and write down what I see? Not really, land snails are generally only active for a small proportion of the day, and even if you can observe them feeding it’s hard to tell what they’re eating. The lettuce-destroying slugs and snails we are familiar with are the odd ones out in the malacolgical world – most land snails don’t eat live plants, instead, they prefer decaying matter or algae and fungi growing on various surfaces (some others are carnivores). So, to try and learn something about the diet of my land snails I broke out a scalpel and started collecting the gut contents from my preserved specimens and picking through them to see what they’ve been eating (and if there are differences between species).

I’ll talk about those results one day, but while I was doing those dissections I started finding and more of the leaf veined slugs I’ve written about before. Including babies:

Which made me think: what are these guys eating? As ever, I turned to google for an answer and Te Ara had it “their biology is poorly known, but they are thought to live mainly on algae and fungi on the surface of plants”. Sure enough, searching through the literature on the 30 or so species of leaf veined slug in New Zealand, there is no indication of what it is that they eat. That was too depressing for me, we know so little about the biology of our native invertebrates, but this species (Athoracophorus bitentaculatus) isn’t particularily rare, we should at least know what this one eats.

Don’t worry, I didn’t start sacrificing cute little slug-lets in the name of science. There’s another way to get gut contents (note also, that even flattened slugs have the strangely twisted anatomy of the snails from which they descended):

So, I took to stepping outside an night time, finding a couple of slugs, and placing them in a bucket. In the morning I’d move them back to the shrubs from which they’d been plucked and scoop a few fecal samples out of the bucket to inspect along with my dissections. And here’s what I found when I looked down the microscope:

pollen2

And a little closer:

pollen

It’s took me a pretty long time to work out what these three-lobed structures were, but I’m pretty sure I know now. They’re pollen grains. You can tell a lot about the world from studying pollen grains, each year plants put out millions of these structures, each once identifiable to a taxonomic group. To a trained eye, a series of pollen samples from a old lake bed can reveal past climate change or the evolutionary history of our country. Pollen can even solve crimes. To my eyes… well, I think these are from the massive pine tree next door ( the smaller lobes are “bladders” designed to catch the wind and let the pollen fly, and are unique to pines and their relatives).

It’s not actually clear that the slugs were going out of their way eat pollen, it might just have been on the surface they were eating from and unavoidable. It’s certainly clear that a lot of grains made it through the digestive system intact. So I still hadn’t really cracked the mystery of what these guys were eating. Then, a couple of weeks ago I noticed something. The railing along the pathway the leads down to our front door is covered in algae and fungi, with a very distinctive pattern:

These are slug feeding trails. As they slide across a surface, slugs and snails use an organ called the radula to rasp away and remove the food. I must have walked past this evidence a thousand times without ever thinking about it! The next night I went out with my deeply amateur night-shoot gear and, sure enough, there the slugs were:

So, now we know, leaf veined slugs do indeed live on algae and fungi (and possibly pollen too) but not only on the surface of plants!

I don’t know how I managed to write this post without checking for similar posts at Snail’s Tale’s by Aydin Örstan, the blogosphere’s preeminent malacologist (I’m sure there’s a trophy for that). Remarkably, Aydin has found pine pollen in fecal samples from slugs, and has found feeding tracks left by the same species! Perhaps his Arion and my Athoracophorus fill the same niche on opposite sides of the world.

Hello boingboing readers! If you want to find some more backyard science, I’ve also been keeping an eye on a little colony of spiders (1,2,3) and I once tried to find out what makes bumblebee workers get working. If you’re a fan of spineless creatures in general, you should check circus of the spineless which collects posts from all over the web (and all over the world). The last edition was hosted by Zen Faulkes at Neurodojo and you can find the older ones here.

Sunday Spinelessness – Updates David Winter Dec 19

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I’m going to round out Sunday Spinelessness for 2010 with a few updates from the creatures that have featured here over the year. But, since this is going to be last post here till the first week of January or so, I’m going to start by taking just a moment to wish everyone who has commented on, linked to, tweeted about or just read The Atavism this year a merry Christmas and an enjoyable break over the new year. I enjoy writing these posts for their own sake, but it’s much more satisfying to be part of a community (no matter how small a part!) of people that are interested in the same ideas I am. Thanks.

Right, now own with the spinelessness. The little green spiders I’ve been following, and sacrificing in the name of science are still going strong. Since the last time I wrote about them I’ve seen them grab prey for the first time (confirming the suspicion that they are ambush predators) and seen males fight for the right to mate with a female. Sadly, I didn’t photograph either of these events (well, not in a way that I’d want to show other people, but there are descriptions of each tucked away in my notebook). I can, however, show you the result of those matings. About three weeks after the first one I started spotting these across the agapanthus:

At last count there were about five separate leaves sporting one of these egg sacs and a watchful mother. One very dedicated mum-to-be actually has three on the go at the moment!

I’ll have to wait a while to see the next generation of the little green spiders, but the leaf-veined slugs that featured along side them here have already moved into the next stage

I haven’t seen a full-sized slug in a long time. But these immature ones are out and about every evening, I’ll have a little more to say about them in the new year.

The pittasporum “pysllids” are still dancing, but no longer at plague proportions. There’s no respite for the pittasporum though, now it’s being devoured by leaf roller moths. If I cared more about the tree I might spray it with insecticide but while its pests are feeding animals as wonderful as this spider (anyone have a clue on an ID?) I’m happy to let them have it:

Finally, the bumblebee nest at the bottom of the garden appears to be enjoying the run of hot weather we’ve had here. Some of the bees in our backyard (no necessarily the ones that live at the bottom, since bumble bees can forage several kilometres from their base) have taken up a slightly odd habit. On a couple of warm evenings I’ve popped outside and found bumblee bees asleep inside foxglove flowers:

No doubt the little tubes make a nice warm place for a worker to spend the night if they are caught out too late to make it home. Apparently males, which are only produced towards the end of summer, will often do the same trick once they’ve left the nest and are spending their daytime waiting for a virgin queen to pass by. I think we really have to end with a bumble bee bum sticking out of a flower:

Sunday Spinelessness – A leaf veined slug David Winter Oct 10

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You see some pretty impressive photographs in bug-blogosphere. People like Alex Wild, Adrian Thysse, Ted MacRae and Mike Bok use impressive gear, and much more impressive skill, to serve up wonderful shots of the smaller inhabitants of the natural world. Not so much here. Photographing the subjects for these posts greatly increases the joy that I get from observing their lives, but I don’t claim to have any real skill and, except for that one time, the photography around here is all point-and-shoot. But I’ve never shared anything quite as amatuer as the photos I’m about to show you.

Earlier this year I bought Ray and Lyn Foresters very cool book on New Zealand spiders, and read about the genus Celaenia, the members of which spend their evenings dangling from a thread impersonating a female moth (in both look and scent) in the hope of making a meal of a male moth. I thought I should spend at least part of one of my evenings seeing if I could find any Celaenia in our garden. And so it was that I found myself out in the cold shining a flashlight into bush after bush looking for spiders and discovering only a bright yellow slug:

At first glance I presumed it was one of those lettuce destroying introduced species, perhaps Limax flavus, but most of the slugs introduced to New Zealand have cylindrical bodies and pronounced mantles (the organ that would have made their ancestor’s shells and ends up looking a bit like a saddle on the front of the slug) and this one is flat and has no obvious mantle. In fact, this is native slug, from a pretty cool family. So, I just had to try and photograph it. There is no way the flash on my camera can illuminate a subject less than a few metres away, and no way its lens is going to record any details in a subject more than a few metres away. So, i stood outside, in the dark, with one hand pointing a flashlight at a slug and the other holding my camera away from me, with neck strap held taught in the hope this pose would stabilise the camera enough to get some sort of shot to share with you. It’s really a miracle I got anything from about ten minutes of that farcical photo-shoot, but here you go:

Now you can make out the patterns that give these slugs their common name – the leaf veined slugs ( I have no idea what the taxonomic name for this family, Athoracophoridae, refers to). This species, probably Athoracophorus bitentaculatus doesn’t have the prominent colouring that some if its relatives do, but you can still see the “veins” as furrows running through the rougher parts of the slug’s skin. We have about thirty species of of leaf veined slugs in New Zealand and, like most of our land-living molluscs, we don’t know an awful lot about them. Massey University’s “soil bugs” site (which is pretty awesome by the way) has a gallery of leaf-veined slugs, which includes surely the cutest mollusc you’ll see today.

Lately I’ve been spending one day each week in the lab dissecting the landsnails that are the subject of my PhD. The most common question I get from labmates and anyone that asks what I’ve been up to lately is “how do you know which bit is which”. I understand the sentiment, because looking back on my notes I clearly had no idea when I started, but I think between Aydin Orstan’s photos and a side-by-side comparison of this slug with this diagram of its internal anatomy you can at least get a feel for the lay of the land.