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)




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