Ghosts in the shell

You probably don't know, but I have a pet giant African land snail (Achatina fulica) called 'Chickpea' because that's what s/he (the species is hermaphrodite) looked like when young. S/he's now a bit larger and 'Brazilnut' might be more accurate.

Chickpea the not-yet-giant African land snail.

However, the keeping of exotic invertebrates is not today's topic. While cleaning Chickpea's tank, I noticed some tiny white dots moving rapidly around the snail's foot and disappearing behind it. Of course, I grabbed a camera and then went online. It didn't take long to find out that this was an infestation of Riccardoella mites, probably R. limacum.

Riccardoella mites.

More Riccardoella mites.

I use the word 'infestation' because these are parasitic. They were previously though to be commensal, feeding harmlessly on mucus, but are now known to be blood-feeders. This may not be too much of a problem unless they are numerous, but their feeding can lead to secondary infection via the tiny wounds. They are also difficult to remove as they are very swift and hide in the pneumostome (breathing pore). Rinsing the snail with water is likely to help limit them, and if lucky may remove them all eventually, but the only other known option is to buy the predatory mite species Hypoaspis miles which will target them, although these mites are only available in large quantities for use across whole gardens, allotments and so on up to larger scales. It is likely that the mites came in with the soil used in Chickpea's tank and they are common in the wild, being found on various native slugs and snails. So, I will see if washing works, and if not, maybe a 'mite-share' scheme will do the job. Until then, I don't have access to electron microscopy, but if you'd like more info and some excellent images, I recommend this page.

Focusing on the familiar: butterfly wings

It's a while since I've written anything (workload, the evil flu of doom etc etc), so I thought I'd resume service with a look at something that everyone's at least broadly familiar with, even if not in detail - butterfly wings. You may know that the insect order Lepidoptera (butterfles & moths) means 'scaly wing', and that's because the wings are covered in many tiny scales that effectively work like pixels to make up the overall pattern.In December a very fresh looking peacock butterfly Inachis io was roosting in our house, presumably hibernating, so I took a couple of pictures.

Peacock butterfly Inachis io

One of the 'eyes' in the wing pattern - individual scales are clearly visible.

Near the base and front edge of the wing - again you can see individual scales.

I could put the wing under a microscope and get more detail, but I didn't want to disturb the butterfly while it was roosting - instead, there is a light microscope image here, and electron microscope images (which I can't produce!) here (x1000) and here (x5000). The last one is important becuase it shows one way that scale colours are formed.

Browns and blackish colours are formed by melanin pigments in the scales - the same type of pigment that we have in our skin, hair and the irises of our eyes. However in most cases the brighter colours - reds, greens, blues and so on - occur because of iridescence caused by the microstructure scattering light in different wavelengths depending on the precise fine structure. If you have a microscope, the scales brush off easily without damaging the wing (you could use a small soft paintbrush then transfer them to a slide) so why not have a look at the scales - if you don't want to disturb a live butterfly or moth, you can wait until a dead one turns up. Happy scaling...