Tuesday 28 August 2012

The Hornet mimic Large Alder Sawfly

One of my first posts at BugBlog dealt with a strange caterpillar I was unable to ID. The caterpillar turned out to be the larvae of a rare sawfly, Cimbex connatus. The following summer I came across an adult, but it was dead and squished, so I never blogged on it. Today, just coming out of work I spotted what I thought it was a hornet on the ground. I got very excited, as I have never seen one, but my excitement turned quickly into disappointment and then into more excitement when I realised that it was in fact an adult, alive - although on its last legs - Cimbex. This is an awesome European hornet mimic, down to the abdominal pattern, size and general colouration, including the wings, and general body shape. @RichardComont at Twitter identified it as Cimbex connatus, the large alder sawfly.
Sawflies are a large and heterogeneous group in the hymenoptera, the order that includes stinging insects such as bees ants and wasps, although sawflies are harmless. The family to which Cimbex belongs has characteristic clubbed antenna. Males have enlarged hind legs and mandibles - which apparently use to fight with other males for access to females. Females have a saw-like ovipositor. They lay their eggs on specific trees or bushes and their caterpillar-like larvae feed on the leaves and come to the soil to pupate. 
I believe my specimen to be a female, as she has got an enlarged abdomen with the ovipositor sheath being visible underneath it. It measures 21 mm. I mounted it on a piece of white tack to photograph it in a more life-like position.

A side view of Cimbex connatus
A front view reveals a fierce-looking face, with large, sharp jaws and clubbed antenna.
This species is one of three large Cymbex species found in the U.K. it was regarded as extremely rare if not extinct. According to Mark Boddington:

Following a half-century hiatus to 1997, we have recent records of Cimbex connatus (Schrank) from more than ten counties in southern through eastern England, reaching as far north as the Humber. Over much of this area, C. connatus is now comfortably the most frequently encountered member of the genus, followed by C. femoratus (L.) and C. luteus (L.), the latter species in particular being infrequently seen. 

The expansion of Cimbex connatus in the UK might be linked to the increasing use of Italian alder trees, Alnus cordata, and similar species to line avenues in towns and cities.
Cimbex connatus larva found under Italian alder (23/09/2008)


Janet Steedman said...

One of these flew into my pond in Llanfihangel Talyllyn, a village near Brecon in Powys.
I fished it out and it flew away before I could photograph it, but I'm sure it was cimbex connitis. It was huge- about an inch long, yellow and black and it buzzd very loudly in the water. Is wings seemed to me to be rather small compared with the size of its body. I'm sure it wa glad to be rescued because the fish would have had it. I'll keep a look out for any more.

Unknown said...

Brookings, Oregon, USA I got a good photo of a cimbex connitis yesterday. Never seen one before, VERY fierce looking, I did not mess with him, just took the photo and left him alone...I can post it if anybody is interested?

Sue said...

I've been watching a small row of Italian Alder for almost a year after finding some strange green caterpillars which took ages to identify. Hoping to see a sawfly soon.

Sue said...

I'd love to see your photo please. I've just posted as unknown and am just off to check my Italian Alders.

Keeping track bookkeeping said...

Well, we have been panicking for three days. Found this sitting on edge of our pool . People on line came back with we must report this it’s an Asian hornet etc. So fierce looking. Managed to get in jar and take pics and report to Defra. They came back today sayin it’s a hornet mimic sawfly and harmless so glad to say have let it free. Have many many pics close up of face etc if anyone wants ? Don’t know how I post pics in here !!!!

Africa Gomez said...

Thank you for commenting, but not, I don't think photos are allowed as blog post comments.

Anbu said...

I just found one last night in Utah, my dogs were trying to get at him, not sure how to insert pics

Dinah Badcock said...

I found one, on July 26th 2020, acting sluggishly, on a Shasta daisy in our flower border in Kent, but was fooled by its disguise and didn't recognise it. Apparently it's still quite rare and didn't feature in my books. It was released the following morning but still didn't fly.

Clint Jenson said...

Just was walking outside and one landed on my shoulder, I heard it land and thought it was a pine beetle and swatted it and stepped on it before it bit me. I then looked at it and realized it was something different and thought it was an Asian hornet. I started googling it and found this blog but what’s interesting is I live in Northwestern Ontario Canada.