Thursday, September 06, 2012

Possibly a first for Kent...

Having allowed a few days to pass since my last update, I re-visited the spot where I located the shieldbug nymphs. I was hoping to perhaps find some parent bug instars this time.
These little nymphs are quite impressive in their stripped waistcoats and having found adults, I was optimistic...

Elasmucha grisea
My enthusiasm may have been a little misplaced, as I only found one individual today, but I was pleased with one and surprised at how much detail I managed in a natural light shot of it. 

Here's where the story got interesting for me, and why I wanted to link this blog update with the last.

What did I originally find here? Well, a Birch Shieldbug and a Parent Bug. Both of these species are associated with the birch tree. I have to admit to not examining the bark of the tree but did look at the leaves, and yes, they looked like birch.
A reasonable assumption would be that it was a birch tree then?

Well yes, but then when I returned a few days later I found a cracking little sawfly larva on the same tree...

Cimbex connatus
And what's so special about this particular sawfly larva? Actually quite a lot!
It seems that it's something of a rarity:at least, until recently anyhow.

The U.K. status is listed as follows: Once thought to be extinct in Britain, it was re-discovered in Wiltshire in the 1990's and has since spread through southern England.

Here's an NBN Gateway map for the species...

As you can see, there only a couple of records .Probably under-recorded to some extent, but still a nice find with no records in my area at all.

A Large Alder Sawfly larva
I've given this dorsal view its common name to illustrate how all this fits together.

And so this is an Alder Sawfly-not associated with birch then? So now we have on the same tree, two species correctly associated, and one not. O.K. no problem, it's quite common for a species to be found on a plant or tree other than the preferred choice. 

If the discovery of this sawfly larva was noteworthy for its rarity value, then my next find must be considered equally of merit for different reasons and top of the list would probably be something along the lines of 'what the heck...'

Eriocampa ovata

These larvae can grow up to 2cm long and are covered in this white powdery substance. This is supposed to protect them from predators who mistake them for bird-droppings. The white camouflage is easily rubbed off and in the final instar, when feeding is complete, the white powder is lost and the larvae adopts a pale green colour...

This sawfly larva is less rare than the previous, with at least a few records for Kent but most of the sighting do seem to have come from the south of the country.

And what's the common name for this species? The Alder Sawfly or sometimes The Woolly Alder Sawfly. we have two species assoc. with birch and two alder, all of which were found on the same tree.

Time to check this out then! Back for another, better look at the tree and the surrounding habitat.

Result: There are other alder trees close-by, alder are often found beside water (as this was) and on closer inspection the leaves have hairs on the underside. 

Conclusion: this was indeed an alder tree and not birch after all. Why then are two species of shieldbug closely associated with birch feeding on alder? I've not heard of, or indeed found this before but a safe guess would be that alder and birch actually belong in the same family of 'Betulacae'

I have to admit to finding this fascinating and really enjoyed the research into finding identities etc. I have yet another uncommon insect that I found this week, but I'll use this one as a little teaser to my next blog entry, which should be along any day.

Until the next time then...


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