Tag Archives: Pseudisobrachium subcyaneum

Rare versus obscure?

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At 5 mm long, narrow, and black, Pseudisobrachium subcyaneum is understated, to say the least.

This is perhaps the rarest insect I’ve seen this year. Or it may just be the most obscure. The Bethylidae are technically (along with bees, wasps and ants) part of the Aculeata (they mostly have stings at the pointed end), but whereas those more familiar insects have a popular following and at least some popular recognition, bethylids are mired in darkest obscurity. This is certainly the largest bethylid I’ve ever seen, but at just over 5 mm it is minuscule beside yellow-jackets and bumblebees.

I like the bethylids, mostly because I started finding them when looking for beetles. They have a most un-wasp-like way of running around in the sweep-net, not flying, rather like a tiny rove beetle; they are dark, parallel-sided with shining thorax and a triangular or pentagonal head a bit like Sunius or Rugilus. I now have quite a collection of them thanks to my confusion.

It seems likely, though, that most other coleopterists ignore them, as do most hymenopterists. Consequently they are poorly understood and seldom recorded. There are zero records for Pseudisobrachium on the National Biodiversity Network database. According to the Bees, Wasps and Ants Recording Society page, there are old (19th, or early 20th century?) records for Kent, Surrey, Isle of Wight and Dorset; the only modern record is from South Essex in the 1990s.

This is a male; females of Pseudisobrachium are blind and wingless and possibly live in some association with ants, although nobody seems quite sure. This does mean that as a species it is very poorly adapted to finding and colonizing new sites, but well-suited to declining and become locally extinct.

I found it near Hounslow Heath, a worthy remnant of sandy heathland in west London. Sadly this area is under constant threat from urban encroachment, development and habitat degradation. There is now nothing remotely heathy about the once richly biodiverse Heath Row a few thousand metres away north-west, now buried under runways, hangars and shining terminal buildings.

The single specimen, swept on a sunny but cool 15 September, was just outside the genuine Heath, on the abandoned golf course. Here, a year after the course closed, the fairways have grown into long grass, but apart from some yarrow, plant variety is almost a herb-poor monoculture of coarse grasses. The only variation was in some of the old sand bunkers, and sure enough this is where Pseudisobrachium occurred.

Golf courses have a mixed reputation for nature conservation. On the one hand they are green open spaces with roughs and copses and hedges and trees, but on the other they are sometimes savagely manicured to within an inch of their wildlife.

But if left alone for a short while, strange creatures may eventually crawl out of the hazards — even if they are tiny, mysterious creeping things about which we know virtually nothing.