Dear Readers, after my adventures with the hornet-mimic hoverfly last week, I was keeping an eye open for other new-to-me species today, and spotted this hoverfly sitting on my sedum (some of which is already in flower rather earlier than usual). This species is sometimes known as the ‘Batman hoverfly’ because if you squint, the pattern on the thorax looks rather like the ‘Batman’ symbol that lights up the sky above Gotham City when something particularly nefarious is going on.
I can tell that this fly is a female because there is a tiny gap between the eyes – in the males of many genuses (genii???) of hoverflies the eyes meet at the top of the head with no gap whatsoever.
Batman hoverflies will breed in anything that holds water, and since I have a pond, a bird bath and several dishes for ground-feeding animals they have plenty of choice. The ‘rat-tailed’ larvae (the ‘tail’ is actually a breathing tube) will lurk amongst decaying leaves and twigs, and their number one preferred habitat is a ‘rot hole’ – a cavity in a tree that holds water and detritus. As the detritus rots down, the habitat in the rot hole holds less and less oxygen, and so the larvae need their long ‘tails’ in order to breathe.
Interestingly, it’s been found that the larvae actually have control over their buoyancy – being naturally quite fat, they sometimes naturally float to the surface of the water, whereupon they expel air and dive back down, rather like miniature long-tailed whales. They can also control the length of the breeding tube depending on the depth of the water that they’re in, as described in this ‘Country Diary’ piece in The Guardian by Phil Gates.
The adult hoverflies have a long flight season, from April to November, and can often be seen happily basking in the sun on some convenient flowers. The hoverfly in my photos sat around quite happily for half an hour while I clicked away. How I wish that all insects were so cooperative!
I am becoming more and more interested in hoverflies, and one suggestion to encourage more species that nest in rot holes, such as the Batman hoverfly, is to create an artificial hoverfly ‘nest’. You can do this by taping a two-litre plastic drinking bottle low down on the sheltered side of a tree. You then cut a hole in it, and partially fill it with sawdust, twigs and water, making sure that you keep it topped up during dry spells. What an interesting idea! It’s easy to forget that hoverflies are excellent pollinators and that they also need a helping hand. Maybe I’ll have a go at this. I’ll let you know how I get on.
And in other news, the frogs are very reluctant to leave the pond this year, and who can blame them? Everywhere outside the garden is absolutely parched. If I was a frog, I would definitely hang around until the rain returns, though with a hose pipe ban in the offing and no rain forecast for the next fortnight, the amphibians could have a long wait.