Posted by Penelope Lovesy at 22/06/2020 11:20:26
The title of part 2 of Pests in Museums is somewhat misleading as some of today’s featured pests could just as easily be causing problems during the day. However, those that aren’t necessarily nocturnal do have an aversion to light. Yes, I know that lots of insects prefer the dark, including some of the last instalment’s stars, but you try thinking of a captivating title or tagline to entice the masses to read about booklice or silverfish!
The first of today’s nuisance insects certainly doesn’t have an aversion to light in its adult life as it is positively phototactic, and some species are happy fluttering about during the day. I am of course referring to moths. I hope you don’t suffer from Mottephobia as this might make you uncomfortable.
I’m sure you’re aware of the popular phrase ‘like a moth to a flame’ but this allusion is misleading. For one, moths don’t like flames; they catch on fire! However, one thing that is true is that adult moths flock to bright light, particularly UV, but the precise reason for this is still up for discussion. Some experts believe it is part of a moth’s self-righting mechanism - the moon is most definitely upwards - while another idea is that light indicates safety; moths fly towards the moon to escape when they’re disturbed from a plant. Once at the light, moths find it difficult to leave because, like humans, a moth’s dark-adapting mechanism responds much more slowly than its light-adapting mechanism. When you’ve been near a bright light and move into the dark you find yourself temporally blinded while your eyes adjust.
So, should you permanently keep all the lights off in museums to prevent moths from attacking collections or install the brightest lamp you’ve ever seen to eternally attract any invaders? Of course not, that’s just stupid. A massive lamp would harm the collection itself and turning the lights off might not be a huge benefit, especially as the dark-loving larvae are responsible for damage (why is it always the kids?!) Moth larvae have very specific tastes such as natural fibres. And while some, like Cinnabar moth caterpillars, will happy chomp Ragwort growing in the garden (especially mine), others prefer the more subtlety seasoned taste of your carpet, t-shirt or smalls…
There are many moths that would enjoy the tasty delights of a museum collection, but we’ll look at just two; the Webbing clothes moth and the Case-bearing clothes moth. The Webbing clothes moth (Tineola bisselliella) is approximately 1cm long, light brown/gold in colour with an orange head. The Case-bearing clothes moth (Tinea pellionella) is 1cm long, light silvery brown in colour with a golden head; I know, pretty much identical! Case-bearing clothes moths tend to walk about rather than fly whereas the webbing clothes moth has an easily recognisable fluttering flight pattern. The larvae are more easily identifiable - one has a case and the other doesn’t, one spins a ‘web’ and the other doesn’t; it’s that simple. Case-bearing moth larvae use the digested fibres to create a case to camouflage themselves against the backdrop of their chosen restaurant, which they drag about behind them. This makes them difficult to spot until they move from one eatery to another that doesn’t have the same bright blue and red décor. Webbing-clothes moths on the other hand create a fine ‘web’ of fibres to protect themselves so they can feast in peace. Both species feed on natural history collections as well as fabrics but the Webbing-clothes moth is more tolerant to damp and often enters collections after feeding on trapped carcases in attic spaces.
Let’s leave those pesky moths aside for now and move on to silverfish, which, in my opinion, are rather beautiful, but equally as dangerous to collections. Silverfish (Lepisma saccharina) belong to a primitive family of wingless insects that feed on carbohydrates, something they can source from just about anywhere. Their tapered shape, colouration and wriggling, fish-like movement earn them their common name but don’t let their diminutive appearance fool you. Silverfish, and their similar looking cousin the Firebrat (Thermobia domestica), desire dark, damp and humid conditions and are particularly fond of eating paper, book bindings or damp cloth. Museum collections contain a cornucopia of edible delights; cotton, silk and linen garments, tapestries or fabrics, carpets, prints, maps, letters, taxidermy specimens, painted material, plaster, glue and even photographs. Inadvertently dropped crumbs, dandruff, hair, remains of insects (like other dead pests) and coffee provide a delicious alternative and in times of ‘famine’ they will even eat leather and synthetic fibres. Poor handling practice can also provide a treat to these wee beasties as unclean hands might leave greasy residues on objects; who wouldn’t want to enjoy a greasy residue or the resultant microscopic mould? Even if food sources dry up, silverfish and firebrats can survive without for over a year on water alone; which is a long time, potentially an entire life cycle in fact!
Apparently, the courtship of silverfish is something quite romantic to behold, being slow and steady. It would probably be quite at home in a Brontë novel, but we wouldn’t want silverfish to be at home in a Brontë novel as they’d just eat it! Due to their aversion to light you probably won’t get the chance to see this entomological marvel but, at home, you may see them scurrying to dark corners or between floorboards in cellars, kitchens and bathrooms. If you really want to watch them pair up while you serenade them by humming ‘Lady in Red’ you could always check behind furniture where they’re probably munching on the wallpaper to get to the mouth-watering paste beneath. As catching silverfish red handed can be difficult, you should watch out for two tell-tale signs of silverfish or firebrats; yellow stained fabrics and feeding scratches across paper, which leave translucent patches and disappearing texts, eventually leading to holes and irregular edges.
Speaking of disappearing texts, let’s complete this edition by learning all about booklice! Booklice is the common collective name for Liposcelis bostrochophila, a member of the primitive and ancient Pscoptera crime family! They got their name because, well, they eat books, but they’re quite the gourmands and will eat everything already listed on a silverfish’s menu. Booklice are only 1mm in adulthood and move incredibly fast when disturbed so it’s almost impossible to catch them in the act. Booklice are parthenogenic, meaning they lay fertilised eggs without the need for male fertilisation; in fact, there aren’t even male booklice. Because of their asexual reproductive adaptation all adults lay eggs, which can be anything between 20 to 50 eggs per lifecycle (anything up to 110 days). The nymphs look like mini translucent adults (which is the same for silverfish too) and are barely noticeable to the naked eye, 0.2 – 0.8mm long. It takes an awful lot of booklice to produce noticeable damage and by the time you notice, the infestation it’s likely to be vast. Being much smaller than silverfish, the evidence is smaller too. Like silverfish they score the paper and leave see-through patches, but this takes time; the slowly fading text as they eat the ink is likely to be the first alarming signs of a problem. It is important to keep a check on printed material and look out for the early signs, but it is important to remember that inks can fade over time naturally without the interference of lice, so don’t run around screaming and throw your books into the fire immediately.
So there we have it, part 2 draws to a close. In the final episode we will look at the methods museums use to control pest and how objects may be treated if they get attacked. Remember; stay alert, control the pests, save collections!