Every year, summer’s first few days of sunshine bring back a wealth of half-forgotten activities and hobbies to our exam-worn lives. Iceboxes and swimming gear are dug up from the hidden reaches of our storage, balconies and gardens become pleasant habitats once more, and we finally remember what sunglasses were for. For some, it means the first of many trips to the beach, to others late evenings in the backyard with a glass of wine, or maybe even a couple of plane rides across the globe. To a select few, however, the taste of summer brings a powerful desire to relive childhood memories and bunker down in their bedroom to breed silkworms like there’s no tomorrow.
Dutch people often look a little puzzled at the mention of the words ‘breeding silkworms’, which is as foreign a concept to them as not planning your entire summer vacation one year ahead. In the heart of Andalusian Spain, however, surrounded on all sides by mulberry trees and a rich history of silk production, silkworms are a still a familiar feature of any childhood, even if there is no longer a Spanish Silk Route to prove it. Every spring, parents and grandparents at my local primary school form an impromptu black market, handing out batches of surplus eggs like they’re distributing free starter samples of crack, and the moment the eggs hatch mulberry trees around town can be spotted instantly by their stripped lower branches.
Kids will dip the leaves in cardboard boxes and watch their caterpillars – at first the mere size of a pinhead – devour them within hours. The little critters will do this for four weeks, multiplying their body weight a rough 10.000 times and reaching the length and diametre of a finger by their final moult (skin shed), by which time they are so massive that at night the pitter-patter sound of their legs on leaves sounds like rainfall.
At this point of explanation, most of my Dutch friends are usually nodding vaguely but also, with a horrified look in their eyes, looking for the nearest exit from both conversation and room. Unfortunately, by then they – much like you at this moment, dear reader – have been ensnared into a half-hour monologue on the silkworm life cycle. Good luck – you’re going to need it.
In any case, now that I have you intrigued (I’m assuming, as otherwise you’d have clicked away from this page and be retching into the nearest wastebasket this very moment), silkworms have your typical butterfly/moth life cycle. As is usually the case, egg stage is followed by larval stage, which enters pupa stage and eventually emerges as its final phase: adult moth. Several millennia of careful selective breeding have altered the specifics of this cycle rather drastically, however, eliminating most of the silkworm’s natural defence and survival mechanisms.
There are no bright colours, poisons or spikes. In fact, the caterpillars’ only protection against predators is a vague sort of shudder if touched (spoiler alert: 0/10 effectiveness against even the dullest, most inbred of predators). The adult moths, on the other hand, have lost the ability to feed and fly, and can only lurch around drunkenly as they waft around their pheromones in a desperate attempt to get some sort of action out of their week-long shadow of an existence (before you ask: no, the sex is boring, miserable, and is followed by the females having to expel half their body weight in eggs. Not worth it), and if disease hits your colony at any point you might as well just pack it all up right there – the current silkworm’s immune system is about as sophisticated as that of a rock’s.
Aside from these rather subpar survival instincts, silkworms do possess some truly fascinating quirks that set them apart from their peers.
One of these is their determination to eat only mulberry leaves, while another is their famous ability to spin a silk cocoon around themselves before they form their chrysalis. To craft this little marvel, they use a single thread measuring up to a kilometre in length and form shimmering, oval-shaped cocoons in hues ranging from pearly white to full gold – as well as the occasional pale green or pink if you’ve managed to get your hands on a special breed.
At this point you’re probably thinking: “Wow, this sounds amazing! I definitely want silkworms now. Please tell me more!”
I enthusiastically agree, and am delighted to hear you have such good taste in hobbies. Therefore, dearest reader and silkworm parent-to-be, let me tell you about silkworm care during all of its life cycle’s delightful phases. Take notes!
- Egg stage
This part of the cycle is pretty straightforward. Whether they’ve been given to you by a friend with great interests or you’ve bought them online (I’ll add some links at the end of this article), the eggs will be a grey colour and about the size of a miracle. My first batch of eggs came from a primary school mother when I was nine and had just moved to Spain. Silkworms were a facet of the new Spanish world I could comprehend (unlike, well, everything else about it), and they were an incredible project for a child my age. Watching them spin a silk cocoon was a transcendental experience, more so because they didn’t ask questions about whether I’d learned when to use Spanish accent marks yet.
In any case, your eggs should hatch within one to two weeks of exposure to room temperature, and will turn blue-green a few days before this moment occurs. Congrats, you’re a parent now – get ready to start posting baby pics on Facebook!
- Larva stage
As the caterpillars emerge, they will immediately be ravenous for some of that sweet, sweet mulberry foliage. My advice to you, however, is to wait about 24 hours before starting feeding them, as this will ensure most caterpillars – which hatch within a day or so of each other – begin growth simultaneously, and prevent differences in size later on. This is particularly useful during their moulting periods, which are my main annoyance during this stage.
Essentially, in order to deal with their disproportionate growth silkworms go through four moults before pupation (a.k.a. forming a chrysalis) each of which starts with them stopping leaf consumption, raising their neck and staying very still for about a day. Then their head will pop off (Monday evenings, am I right?), and they will wriggle out of their old skin, revealing a new, oversized set of jaws that will become anatomically proportionate to them a lot faster than you think is possible. The main issue with these 24 hours is that the caterpillar will be exceptionally vulnerable: if it falls it will be unable to get up again, be incapable of moulting successfully – and will die; if it’s disturbed its fragile skin will break or bruise fatally – and it will also die.
Basically, if silkworms are like a candle in the wind at the best of times, now it’s also raining and there’s a storm. Cleaning and placing new leaves into your silkworm enclosure are particularly difficult tasks during these stages, and having all your silkworms moult simultaneously greatly shortens the length of time you’ll have to navigate this nightmare.
- Start by feeding your silkworms smaller, tender leaves when they are small. Once the first moult is done you can move on to adult leaves. Stock up leaves around this time too, as their appetite will increase exponentially. Some more information about where to find mulberry leaves can be found at the end of the article, although if you’re in the Netherlands you won’t have much luck. There are also links for websites to order mulberry munch from, however, if this does end up being the case.
Protip from an expert: do not try raising more than 100 silkworms at a time. If they seem to fit in one container now, they’ll be overcrowded by the next moult, and the mulberry leaf demand will not be manageable before the end of the second week. Even feeding 50 silkworms in their final moult is hell. Start with 30, and clear a shelf in your fridge to stuff bags of collected leaves in – you’ll need it.
- Pupa Stage
After satisfying your children’s ever-growing hunger for around 4 weeks, your now lumbering, plump caterpillars will start to act a little shifty. They’ll stop stuffing themselves and start looking for a nice corner, skilfully placed toilet roll or other bits of elevated terrain. Then they’ll expel a final liquid poop pellet and start to focus on a particular area of cardboard. This is when the magic happens: silk will spring into existence. Interestingly enough, even as the caterpillar is looking for a place to spin a cocoon, its insides have already started to melt in anticipation of metamorphosis. Sweet, right?
In any case, the initial efforts of your talented, miraculous child will be on creating an outer structure of silk in which to position the actual cocoon. A framework, if you will. Once this is done, the caterpillar will begin to spin a different type of silk, adding a glue in its saliva that ensures the oval-shaped structure hardens as quickly as possible. At first the little sphere its working inside is translucent, allowing you to see the larva hard at work. Eventually, it will be completely opaque, and after a few days it’s done. You can now safely remove the cocoon, if you want to place them in a separate container for egg-laying later. Behind its protective shell, the caterpillar has undergone its final moult and shed its head entirely, forming its chrysalis. If you gently shake the cocoon you can feel the weight shift inside!
You now have about 20 days to enjoy peace and quiet. This is the time for you to clean out the cardboard box or container you hosted the silkworms in, make preparations for the moths to emerge and be able to lay eggs and cry our eyes out because they grow up so fast. It’ll be emotional. It’ll be difficult. You’ll probably start getting symptoms of empty nest syndrome as well. Please resist the temptation to buy a replacement pet – a dog may seem fun and intelligent but it can never replace the warmth, depth and intellectual finesse of your silkworm children. Knowing this is hard but you need to hear it, dear reader – it’s an inevitable part of parenthood.
- Adult Stage
Almost three weeks after beginning metamorphosis your once already beautiful silkworm caterpillars will emerge from their cocoons reborn in an even more stunning form. Cream and white in colour, they have exquisite wings and fur, and their antennae are delicate and feathery. Hatching generally happens in the early hours of morning, so you can easily miss it if the grief of empty nest syndrome has turned you to alcoholism.
In order to break through the hardened layers of silk, the new-born moth secretes an acidic saliva which dissolves its fibres, allowing it to exit but also destroying the single string they spun their cocoon with (this explains why commercial silk production involves boiling cocoons alive before this happens. Once the silk moth emerges the cocoon is no longer harvestable. Silkworms do not have it easy in our world, which is why you should treasure yours). Once they have pulled themselves from the silk prison, they will squirt a rather unappetizing brown sludge from their hindquarters. This will allow them to start unfolding their wings, which will fully develop in a few hours. If their initial emergence was somewhat anticlimactic, once this process has finished they will look genuinely adorable.
Around this moment you will notice several things about your beloved offspring. Firstly, you will notice their temperament has shifted dramatically. Where they were once sluggish, extremely gluttonous and minimally mobile, they are now sluggish, extremely slutty and essentially immobile. Aside from half-hearted movement the moths are capable of fluttering their wings if they think they smell an individual of the opposite sex (I have yet to meet a gay silkmoth, despite my best attempts to encourage them to embrace sexual fluidity. Not even forced marathons of the Golden Girls have done the trick). Secondly, you will notice how intense said sexual frustration is. I’m talking serious sex addiction levels here. Where the caterpillars were once androgynous larvae with minimal sexual difference (technically, cocoon shape and size can be analysed to determine sex, but it’s difficult and hardly a reliable technique), now males and females are easily distinguishable, and very interested in each other. Females are enormous, their bloated abdomen filled to the brim with eggs. At the end of this abdomen is a small organ that expels pheromones to entice males. These are smaller, slimmer and slightly more capable of movement. They are also incredibly responsive to the pheromones, and will enter a flightless frenzy at the slightest whiff of scent, fluttering madly while they throw around their own hindquarters like there’s no tomorrow (in their defence, there might well not be).
- Egg Stage 2.0
Once they find each other, male and female will lock abdomen ends and give a few wing spurts as they enter ‘love mode’, so to speak. They will remain attached for one to two days, remaining completely immobile. Occasionally, opportunistic males will attempt to tackle the lovers in the hope of dislodging the connection and usurping the female’s interest. It’s therefore easiest to separate the couple, and let them get on with it in peace.
Once the fertilization is complete, both parties part ways. The male will continue on its quest for love, perhaps managing to mate once more before things start going south, and the female will look for a nice surface to start dumping eggs on. This surface can be anything so long as it’s porous enough that she can glue her eggs down. Cardboard or paper is preferable, and using baking paper allows you to easily remove the eggs for storage later. Once a suitable spot is found the female silkmoth gets to work, placing 100-400 bright yellow eggs before she runs out of juice. Her life purpose performed at last, things start falling apart – literally. Over the next few days limbs drop off, hair falls out and other bits and bobs start twitching. This is a sad moment for your little family, and by the time the fertile eggs have darkened from yellow to grey most, if not all, of their parents will have passed. My condolences in advance.
So there you have it, a thorough overview of the growth processes of the majestic silkworm. From its highs and lows to, well, more lows, it’s a journey filled with wonder and awe. You will glow with pride at the sight of the first cocoon, retch at the mouldy layers of poop and leaf bits at the bottom of your silkworm container, and cry at the sight of your first unsuccessfully moulted caterpillar now twitching hopelessly in a corner. If you manage to keep enough of them alive into adulthood you will marvel at their transformation, then gasp in horror as it all comes tumbling down post-coitus (story of my life, though without the limbs-falling-off thing).
Honestly, it’s a project that takes up realistic amounts of time for a mere 2-3 months and is eccentric enough people will assume you have a personality if you mention it in conversation.
Still, eccentric or not, you may have started to suspect from this 2000+ word article that silkworm rearing is a topic close to my heart. You’re not wrong. Ever since moving away from my family in Granada in 2016 to study in the Netherlands, the first thing I think of when tree leaves start unfolding in spring is whether they might be mulberries – like the ones that grow in my hometown’s street. Silkworms remind me of cardboard boxes, the smell of fresh mulberry and afternoons where you come home after school to find all the leaves you gave your worms have mysteriously vanished; memories of watching a moth reveal itself from an empty cocoon and wondering whether a miracle has happened. And, let’s be real for a second, what’s not to love about the geometrical precision and skill of a silkworm’s weaving process? They have no real brain, people!
More importantly, in a world where we stand so far from the origin of processed products that we forget where they come from (and at what cost), it’s nice to remember that at the end of the day what we admiringly call silk is little more than solidified caterpillar saliva. Hot, right?
– you can buy silkworm eggs online at http://www.zijderupsen.eu/index.php/producten, or https://www.silkwormstore.co.uk/.
– If you don’t have any mulberry trees in your vicinity, you can buy mulch from these sites as well. Note, however, that this is both less fun, less suited for healthy silk production and that it really, really makes your microwave smell for a few hours.