Ah, petrichor! And beetles and bugs

Ever wonder if there’s a name for that particular smell that happens when it rains on hot dry dust? Well, there is – it’s petrichor.

According to the Oxford Dictionary, its origins are:

1960s: blend of petro- ‘relating to rocks’ (the smell is believed to be caused by a liquid mixture of organic compounds which collects in the ground) and ichor.

Wikipedia gives more:

The term was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the journal Nature.In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, whereupon it is absorbed by clay-based soils and rocks. During rain, the oil is released into the air along with another compound, geosmin, a metabolic by-product of certain Actinobacteria, which is emitted by wet soil, producing the distinctive scent; ozone may also be present if there is lightning. In a follow-up paper, Bear and Thomas (1965) showed that the oil retards seed germination and early plant growth. This would indicate that the plants exude the oil in order to safeguard the seeds from germination under duress.

We smelt it the other day, after a long time without rain. Lismore has had the driest summer in 115 years – the wet season just failed to materialise. Instead of the 100-300 mL we usually get in January and February, it’s been 55 and 34. It feels wrong, and I have to say that I’ve enjoyed a (relatively) less humid summer, but not the hot temperatures that sometimes came with it.

A charming visitor appeared last week. According to both the Australian Museum and the Queensland Museum, it’s a female Lyraphora obliquata. Not much is known about the habits or biology of this species.

Female Lyraphora obliquata, Larnook, Northern NSW

Female Lyraphora obliquata, Larnook, Northern NSW

The colourful bug below was photographed by a neighbour (the graininess is because it’s from an iPhone). It’s the nymph of the eucalyptus tip-wilter bug, Amorbus alternatus.

Nymph (youngster) of the eucalyptus tip-wilter bug, Amorbus alternatus

Nymph (youngster) of the eucalyptus tip-wilter bug, Amorbus alternatus

Brisbane Insects has photos of both the adult eucalyptus tip-wilter bugs and nymphs.

As you know, insects go through many stages before reaching the adult form, and these instars look nothing like the adult or, often, each other. All fun and games for the hapless insect identifier.

Eucalyptus tip-wilter bug

This little thing was in the rain gauge when I was emptying it this morning – yes, we’re having rain at last! The big lump of heat over Australia’s interior that was encouraging the bushfires in NSW, Victoria and Tasmania was preventing the monsoon setting in in northern Australia, but that’s changed and we’re on our way to getting our January average of 155 mL.

It’s a eucalyptus tip-wilter bug (Amorbus obscuricornis) nymph, according to Brisbane Insects.

Eucalyptus tip-wilter bug nymph,  Amorbus obscuricornis

Eucalyptus tip-wilter bug nymph, Amorbus obscuricornis

You all know (yes?) that a big difference between bugs and beetles is that bugs suck and beetles bite (I recently found out that pigeons suck, unlike other birds that have to raise their heads to tip their water down their throats, but that’s another story.) The lovely emerald dove that visits the pot plants on the back deck daily to sip at the water at their bases bears this out. Fancy a T-shirt that says “Pigeons suck!”? If the Big Bang Theory guys were zoologists instead of physicists, we’d have seen one already.) You also know (don’t you?) that insect eggs hatch into a form (“instar”) that is not like the adult at all, and that the first instar changes into other body forms, five in total in this species, before the adult (reproductive) form is reached. The Brisbane Insects site has a photo of the adult of this nymph, and says, “The bugs feed on new shoots of Eucalyptus trees.¬†They [are] usually found feeding on new shoots of gum trees during sunny days. … The first two nymphal instars of this species are green and black and the last three are orange and black”.

The eucalypt tips were already wilting without the help of these bugs, but maybe that’ll change now.