Small deaths

Spiders are both predators and prey and sometimes we see one in each role in the same, fatal, encounter.

The Daddy-longlegs (Pholcus sp.) in these photos lives quietly between my computer and the wall, waiting for anything edible to come by. (It is probably a direct descendant of this family, since there are always a few in the area.) Jumping spiders, on the other hand, are roving hunters and this little brown one (I thought it might be Servaea or Simaetha sp. but have been reliably informed it is a juvenile Hypoblemum) was on the prowl when it blundered into a strand or two of web.

That had just happened when, by pure chance, I reached around to plug in a camera lead and saw what was going on. The daddy-longlegs, outweighed two to one, took care to stay at a safe distance as it used those long legs to further entrap its prey in silk. The process took a couple of minutes and the jumping spider never even looked like getting away. When it was secure, the daddy-longlegs finally came down to sink its fangs into its victim.

Most of us, I think, automatically (and not always logically) choose sides in a conflict like this. If it’s between a lion and a deer, we tend to sympathise with the deer; if a kookaburra and a snake, we’re on the bird’s side. Cat and gecko? Bird and butterfly? Bird and spider? We don’t always side with the hunter, or with the hunted, or with the vertebrate against the invertebrate, or the mammal against the reptile. What do we think about spider vs spider? Or spider vs fly? More interestingly, perhaps, why do we think whatever we think?

The other ‘small death’ I saw yesterday was, in fact, spider vs fly: one of our larger jumping spiders, Mopsus mormon, had captured a soldier fly:

mopsus mormon
Jumping spider with soldier fly on galangal leaf

 

Predator

As I said a few months ago, “When I started taking a real interest in invertebrates, flies were the group that surprised me most. Time after time, something I thought was a wasp or bee, even a dragonfly, turned out to be a fly.” Here is one that lives a dragonfly lifestyle, an active, agile aerial predator. It is a Robber Fly, Asilidae. 

Robber fly and bee
Robber fly, Asilidae, and Blue-banded Bee, Amegilla sp.

It is quite large by insect standards, nearly as big as a dragonfly but much more heavily built, and its strength allows it to take much larger prey. This one has caught a Blue-banded Bee (Amegilla sp.) and is perching on a Pentas stalk to consume it. I have also seen them with Soldier Flies (almost bee-sized) and, amazingly, one with a Cicada as big as itself.

There’s a good article about Robber Flies on wikipedia if you would like to know more.

Wasp and leaf-hopper


Black wasp on the ground
Black wasp, just landed

This wasp landed on the paver near a large plant pot and sat there buzzing its wings for a moment, as shown here, and then crawled to a drainage hole in its base and walked inside:

Wasp crawling into the base of a large flower pot
Crawling into the base of the pot (how does it keep its wings clean, I wonder?)

A week or two back, I saw a similar wasp carry prey to a hole in the top surface of the dirt. Together with the one entering the bottom of the pot, it had me wondering whether the whole pot was tunnelled and whether the roots of the plant (actually the Desert Rose which the Sunbird was raiding for nesting material) were being eaten by wasp larvae. The answer to the second question should, I realised, be ‘no’: bugs which carry other bugs home as food were not likely to be root-eaters.

Wasp in flight with prey
Carrying prey towards her nesting site

Here we go again … carrying a leafhopper towards the drainage hole in the bottom of the plant pot. What she didn’t know was that we had re-potted the plant, because it had been looking sickly, since she dug a tunnel there. In the process we saw quite a lot of white Leaf-hoppers in the dirt (maybe a dozen) but no network of tunnels, no colony of wasps and no root-eating grubs.

Finally, here she is trying to re-dig her tunnel while still holding the prey. It didn’t work very well and she flew off again with her load. I saw her fly to a nearby plant and stop for a rest but didn’t see what happened after that.

Wasp trying to tunnel into the pot with a leaf-hopper between her back legs.
Now, where's my hole?

One of the experts on the Flickr Field Guide to Australian Insects kindly identified the wasp for me as ‘a Gorytini wasp, perhaps Austrogorytes sp., Crabronidae’. All Crabronidae are solitary wasps which provision nests with paralysed prey as food for their larvae. The biggest of them take cicadas – they must be a lot bigger than my wasp here which is only about 10 mm long and preys (exclusively, going by what we saw in the dirt) on Flatid leaf-hoppers like these.

Orchid – fly – spider

Spray of purple orchids
The flowers

While we’re on spiders, and particularly flower spiders, here’s another – in a setting which neatly demonstrates cause and effect in the food chain.

Our golden orchids flowered a few weeks ago and a purple one followed suit last week. The golden orchids are almost scentless (as far as I’m concerned, anyway) but the purple ones have a strong, sweet perfume which obviously attracts our (in)famous Queensland Fruit Fly, Bactrocera tryoni. There were always a dozen or more of these on the orchid spray, and they came to it last year as well although I don’t usually see them around the garden at all.

A careful look at the orchids revealed another kind of creature on them – flower spiders, there for the fruit flies. The brown one pictured was the bigger of two that I found; the other was the same species as the Flower Spider which caught the wasp, but a smaller individual. Both belong to the same family, Thomisidae, commonly known as ‘Flower Spiders’ and, perhaps mystifyingly, as ‘Crab Spiders’ but I haven’t got a more specific identity for the brown one yet.

Queensland fruit fly on orchid
The fly
Brown and white spider on orchid
The spider
Spider and fly on orchid
Relative sizes

Here’s the Thomisidae family description from Ron Atkinson’s Find-a-spider Guide, which incidentally explains the origin of the common names:

The body is small to moderate in size. The abdomen is somewhat large and more variable in shape than the cephalothorax. The legs are visibly spiny, especially the first two pairs which are very robust and curve forwards in crab-like fashion. The body colour may be white, green or brown to match the colour of the surfaces on which the spider is most likely to be found. The usual habitats are on leaves, in flowers or on/under bark. In the last of these habitats the spider’s surfaces are roughened to improve the camouflage.