Urine, Butterflies and Moths

How to catch a purple emperor

What can urine be good for? Ask people and the answer would probably be “it’s the body’s waste; it’s no good for anything” (well, had you asked Morarji Desai he would have given you a surprisingly different answer!). Anyway, as a high school student, I used urine and formalin in an experiment that was designed to show how the urea in human piddle can be a basic component of plastics. I enjoyed that experiment and believe children today would also enjoy this bit of chemistry. Anyway I was reminded of that high school experiment in Trinidad, when I met a ”Lepidopterologist” (someone who loves collecting butterflies and moths), who explained to me that the best way to attract certain species was to soak a piece of cloth in human urine and hang it into a tree and wait for some winged “jewels” to arrive.

But why would these beautiful creatures find something so revolting like human piss (well, Morarji Desai would have a different opinion on this) so attractive? It’s because of the salt in it: flowers may contain nectar and pollen, but no salts. That’s why you can sometimes see butterflies and moths drinking from a puddle, but it need not be just urine that’s attractive to our friends, the butterflies (and moths). In fact, some serious research has gone on to find the most attractive odoriferous lure, because some species, whose caterpillars are serious pests, first need to be attracted to the being killed.

Fruit odours have been tried and can be successful in case of certain species, but far too many flies also find the fruit odours irresistible and therefore fruit odours are not ideal. That’s why wine-based and beer-based baits were compared with each other by the two Swedish researchers L.B. Pettersson and M. Franzén. These two entomologists used a device known as the Jalas moth trap that consists of a funnel-shaped top into which a small container with bait is hung. This baited funnel is then put onto a wide glass bottle that contains a small open flask with chloroform. The authors of that study discuss whether perhaps different kinds of beer or wine could have led to different results, but in their own study both wine and beer-based traps gave similar results. They used 4.5 litres of red wine to which white sugar was added “to satiation” (I’m wondering if French or Spanish or perhaps Chilean and Australian red -my favourite- would all have been equally attractive, and intoxicating, for the moths) and they used an equal amount of beer. To the latter they added 1 kg of molasses, 1kg of white sugar, 500 g of brown sugar, 230 g of honey, one grated apple and 3 g of yeast. They waited for a week and then 5 wine and 5 beer-bated traps were allowed to “catch” Lepidoptera for 48 hours. And the result? 365 individuals representing 35 species were caught and both traps performed equally well! I suppose traps with no bait caught nothing.

That far more unusual baits can and are being used to lure the largest British butterfly with a wing span of up to 8cm to places where it can be photographed has been reported by the BBC. It’s the majestic and beautiful Purple Emperor (Apatura iris), which is said to feed on rotting flesh, but which also finds faeces, dirty nappies and human sweat very attractive. Some enthusiasts claim smelly cheese also works well. And how does the Purple Emperor detect these to it seemingly irresistible smells? It uses its antennae as its nose, for on it there are the olfactory receptors, special hairs that will be the topic of another blog.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2020.
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