So I know I’m not the only one who’s enjoying today’s brief respite from the heat wave. In spite of covering myself in sunblock, drinking loads of water, wearing a hat, etc., I’ve still been really suffering with the heat, including SUNBURNED FEET! (Mental note to sunblock my feet when I’m in sandals!) I thought you might like to see one way that nature deals with the problem – the spectacular St John’s Wort Leaf Beetle!
This fab little metallic bronze beetle feeds exclusively on St John’s Worts (Hypericum spp., giving the beetle its scientific name: Chrysolina hyperici). The botanists and herbalists amongst you may know that although St John’s Wort is prized for it’s medical properties (it’s used for treating depression, anxiety and insomnia), one of the side effects is increased sensitivity to sunlight. This is due to a toxin called Hypericin. So how is it that our glam little beetle can feed all day in full sun on a plant that should by rights make doing so dangerous?
The theory is that the magic is in the beetle’s wing casings (called ‘Elytra’ – actually modified front wings which cover the second pair of wings which the beetle use to fly with – a common arrangement in beetles -think about ladybirds flying, holding up their elytra and flying with their other pair of wings!). The reflective, opaque elytra actually block all but .01-.2% (Fields et. al, 1990) of the harmful rays of the sun, allowing C. hyperici to forage in full sunlight! So what does it do when it’s a larva and doesn’t have the protection of its super-sun-blocking elytra?? – it feeds only at night and buries itself during the day!
If you see St. John’s Wort around, it is always worth checking to see if this beetle is present, as it is very likely to be under-recorded, with records at only a few sites within the West Midlands. – The bronze colour and paired rows of dimples (called punctures) set it apart from other similar beetles C. brunsvicensis (which has rows of punctures, but not in pairs) and C. varians (which has punctures all over the place, but not in rows).