Tags
British springtails, harlequin ladybird, hoverfly larvae, ladybirds, springtail, Syrphus sp larvae, Syrphus species
Last week, before our current cold snap (though we’ve had no snow, it was -8C in the bitter easterly wind today), I was amazed at how many insects I found on and around a black metal fence that borders a local park.
I was initially checking for hoverfly larvae, as I was alerted a couple of years back to the fact that they can often be found on fences and other objects under trees like Sycamore – I think they fall when the leaves fall, then stay on the fence rails gobbling up any aphids that also fall. The four hoverfly larvae I found (shown below the lovely blue-bodied fly) are all from the Syrphus genus (but it’s not possible to identify them to species level), but I was surprised to also find an abundance of Springtails and more than 20 ladybirds, almost all Harlequin. I don’t know why the fence attracted them all – it felt cold to the touch but perhaps the black paint meant the surface was warm when the sun did actually shine.
The heat absorption/retention of black paint may be a factor, although I’d expect the conductive heat loss due to the underlying metal to more than outweigh it at low ambient temperatures.
Another explanation may be that smooth, dark, painted surfaces often polarize light horizontally, in the same way that the surface of water does.
Many insects use horizontally polarized light to ‘detect’ water and get confused by smooth dark surfaces, even to the extent that some painted surfaces can “look more like water than water”.
See, eg, https://www.newscientist.com/article/dn16380-wildlife-confused-by-polarised-light-pollution/
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How absolutely fascinating, Jon. I had no idea about this and I’m heading over to that link right now. Thanks very much for sharing!
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