Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Friday, February 06, 2009

Tiny Assassin Bug - tracking down an ID.

I spotted this tiny insect walking along the ledge above my front door, last night.
I thought that it was a minuscule Preying Mantis. But, on very close examination of the images, I realised (eventually) that I had photographed a kind of Assassin Bug.

All these images will open to "screen-sized" images - click on them to open the larger file.

I have seen images of these creatures on various Insect Websites, and thought that they were quite large. My creature was no more than 1.5cm long (antennae extra). It walked in a swaying motion, almost like two-steps forward, one step backward. I could see with the naked eye that it was holding its legs (or pincers I thought) high in the air, in front of it. Note the extremely fine hairs on the legs of this insect (they will become relevant later).
Once I had worked out that it was not a Preying Mantis (nymph) (its head was not at all the same shape as a Mantis), I thought that it must be the nymph (immature stage) of whatever else it was - because it was so tiny.

Then I found a similar creature to mine, on Donald Hobern's excellent site - sets - Hemiptera - Reduviidae sp.

That was a surprise to me. Hemipterae are "Bugs". This doesn't look like any bug I have ever seen (thinking of those oval-shaped Green Vegetable Bugs, and Bronze Citrus Bugs and other Stink Bugs). Anyway, I pressed on with the search, using Donald's clue of Reduviidae.
That took me straight to Assassin Bugs.
Oh, I thought. I've seen lots of images of them, but - aren't they supposed to be much larger? They look so fierce, in wonderful Macro images (the lack of scale is always a limiting factor - as it is in my images as well, unfortunately). Here is a link to the Chew Family's section on Assassin Bugs of many different species. Some great shots there, which clearly show their piercing mouth parts. Its well worth a look at these amazing creatures, if you are not familiar with them.

The wings are clearly visible in this image. Compare them to the link below to the WA Dept of Agriculture website.
Maybe mine is a first or second instar, I thought. (The first few juvenile stages, which look like scaled down models of the adults. They shed their shells at each stage, as they grow. If the adult has wings, they only get them at the last stage - no longer called an "instar".)
Nope. This must be a fully mature adult.
It has wings.
So it has to be an adult, surely? Websites for Assassin Bugs all refer to the instars stages as being wingless.
But so small???

I found this in an American document:
The Reduviidae vary greatly in body size and shape, ranging from small and either slender or robust to fairly long and slender like some walkingsticks. The characteristic that distinguishes them from all other hemipterans is the stout 3-segmented beak that fits into a grove on the prosternum.

The proboscis (or beak) is visible under the head, folded backwards as is normal unless they are feeding. So, this is the diagnostic shot, which tells me it is an Assassin Bug.
Well I still had Donald's images and a family name to work from (Reduviidae). What I mean is that, until I had studied this image very carefully I was not sure of the Assassin Bug ID. But that little glimpse of the proboscis clinched the matter for me.

So off I went to the Insect Reference Collection Database, and scrolled down to the Reduviidae.
Here I found a near-perfect match - Stenolemus bituberus. Extraordinarily close, in fact.

Now this website seemingly comes from the West Australian Dept of Agriculture. Without access to their records, I can only assume it is a WA insect, but perhaps the collection is meant to be "national". Maybe its too much to expect their species to be the same as mine. But gosh, it looks close. Compare the shot (2 above) which shows the wings clearly, with that linked image.

Note the very fine hairs all over the legs (on that WA reference image). That tells me something else - the scale. It is obviously a tiny insect, photographed up-close (theirs is a "pinned specimen"). Mine was a tiny, live insect, photographed as close as I could get to it (up a ladder on my front porch, at sometime past midnight). Compare the hairs on the legs in my image, and the striations on the legs - with the WA insect. Theirs is a dried specimen, so that might account for the body looking lighter in colour than mine (transparency caused by fluids drying up?) That bit is guess work but I am prepared to say that my insect looks a very close match to
Stenolemus bituberus.
I do not have the resources to take this search to the next level, which is to try and track down the distribution of that species. Unfortunately, the relevant CSIRO websites are all down at present. They seem to have a habit of that happening on Friday nights. However, I have found a research paper by biologists from Macquarie University (in Sydney) where they studied this insect "which is commonly found close to the lab in Sydney". That solves the distribution problem for me.


On the basis of the distribution and the close match from the Insect Reference Collection Database, I am now prepared to "claim" my ID as positive for Stenolemus bituberus.

One thing I have learned is that the Assassin Bugs have a world-wide distribution, with a very large representation in Australia.

This particular species is well researched, it seems, and is a spider-eating specialist. It seems to favour House Spiders and "Daddy Longlegs" (Pholcus sp.) It makes good sense that it should be stalking along the ledge over my front door, and around my front porch. Lots of moths bring lots of small spiders - food for this Assassin Bug, it seems.

I hope you have enjoyed this "search" process as much as I have.

It does show how much work has to be done, behind the scenes, when blogging about unfamiliar creatures. I guess I have a head start with Orchids, because I have been studying them for years, and I have some good reference books. But insect are such a problem for me, because there are so many thousands of different types - some less familiar to most of us, than others are.


Tyto Tony said...

Killer post, Denis. Really got your teeth into this one!

Gouldiae said...

G'day Denis,
Wonderful photos of a fascinating species. Looks like it gave you some homework too. Very enjoyable - thanks,

Denis Wilson said...
This comment has been removed by the author.
Denis Wilson said...

Hi Gouldiae - it was the homework which was the most interesting thing.
Hi Tony

Thanks, but your sense of humour is getting wetter!


Snail said...

What a great post! Wonderful subject, excellent detective work and the assassin nabbed at the end!

Denis Wilson said...

Hi Snail
As a matter of interest Donald is going to check the Australian National Insect Collection early next week, and advise. At least it sounds like my ID is a reasonable working hypothesis, as they say.
Thanks for the interest shown by all.