I found this in my yard, Western Australia near Perth. It's about 33mm long and I'm intrigued to find out what it is.
Please view the picture here.
Fantastic picture! This insect is in fact a wasp from the family Tiphiidae, commonly called flower wasps or simply tiphiid wasps.
This particular specimen is a female Thynnine wasp. All female species of the subfamily Thynninae are wingless and can often be seen scaling an elevated structure like a flower or a tree (or in your case, a fence) in order to catch the attention of a passing male. Unlike females, Tiphiid males do have wings and will literally sweep the receptive female off her feet for an extended in-flight mating ritual that also involves treating the female to several easy meals along the way (flower nectar being much more accessible from the air).
Winglessness in female tiphiid wasps finally proves useful when, after mating, the gravid female must burrow underground to find a suitable repository for her eggs, namely scarab beetle larvae. Interestingly, winglessness or brachyptery (reduced wings) in wasps often goes hand in hand with this kind of parasitism and occurs in at least eight other wasp families. This frequently leads to confusion with ants, of course, but you can consult our post on one particularly notorious wasp family with wingless females, the mutillids (deceptively referred to as velvet ants), to learn more about some of the differences.
Thanks for your query,
Alexandra Westrich & the AntAsk Team