Ask 10 entomologists for an identification…

Author Marianne Broug ◦

It started with a pleasant Sunday stroll in the Hills … I was about to sit down on a bench but saw a delightful little blue-winged wasp. I decided to photograph it before sitting down. I thought it would be easy to ID … ah but such is not always the case!

There is an old saying : Ask 10 entomologists for an identification and you will receive 11 different names. I have not seen a Thynninae with such coarse sculpture or amount of hair on the lateral margins of the mesosoma. However, the smooth and hairless sculpture on the metasoma is not usual for Mutillidae which usually have coarse sculpture and hair bands. These images contain features of both groups such is the nature of males in these two families.
Source: Ken Walker, Australian Polistinae and other Hymenoptera²

With such great photos, I thought I would point out a unique feature of the Hymenoptera- the wasps, bees and ants. Hymenoptera possess a sting which many wasps, bees and ants use to parasitise prey or sting to protect themselves. In most insects, the head, thorax and abdomen form a rigid structure and only the legs and wings can move and change position (think of a beetle). The effectiveness of the sting would be markedly reduced, probably useless, if the abdomen could not curl. Imagine trying to sting or inject eggs into a caterpillar if the body could not curl the abdomen to a right angle above the caterpillar.

In most insects, the body is divided into three sections : head, thorax and abdomen. However, in Hymenoptera the body layout is different. The major change is that the 1st segment of the abdomen is fused to the end of the thorax (see image) and is called the propodeum. That means what looks like the thorax now consists of the thorax + 1st segment of the abdomen and so it is called the “mesosoma”. The attachment of the 2nd abdominal segment to the 1st abdominal segment (the propodeum) is extremely narrow and importantly is flexible which allows the remaining segments of the abdomen to be curled even to underneath the body itself. The entire 2nd segment itself is much narrower than the following abdominal segments. Now because the 1st abdominal segment is attached to the thorax, which is called the mesosoma, what looks like the remaining abdomen is actually missing the 1st segment so is called the “metasoma”.

This significant change to the morphology of the Hymenoptera body plan works a treat to allow wasps, bees and ants to use their sting and egg laying tube. Nature always finds a way to solve difficult problems.
Source: Ken Walker, Australian Polistinae and other Hymenoptera²

Thynninae (comment Ken Walker), Crafers - Bridgewater SA © Marianne Broug — *Thynninae* (comment Ken Walker), Crafers – Bridgewater SA © Marianne Broug

george_waldren suggested an ID
Subfamily Thynninae
a member of Thynnid Flower Wasps (Family Thynnidae)
Source: george_waldren, Subfamily Thynninae, iNaturalistAU¹

susanna_h suggested an ID
Subfamily Thynninae
a member of Thynnid Flower Wasps (Family Thynnidae)
shape of abdomen and antennae
Source: susanna_h, Australian Polistinae and other Hymenoptera³

I had a look at the curator who offered the Thynninae identification and he does have publications on both Mutillidae and Thynninae. I’m happy to accept the Thynninae identification.
Source: Ken Walker, Australian Polistinae and other Hymenoptera²

Footnote & References