I thought I was done with parenthood. But the tortoises had other plans | Emma Beddington

An unexpected thing has happened: I, we, have had a baby. A surprise change-of-life baby! That wasn’t part of our empty nest plan, but sometimes fate decides and you’re dragged along for the ride. You probably want details: well, we’re not sure of the sex, but it’s probably female because of the incubation temperature and the fact it weighs 17g. OK, it’s a baby tortoise.

Our new arrival came as a complete shock. Our two female tortoises sometimes lay eggs, but none have ever been fertile. One male is a foul sex pest who molests them tirelessly, but we assumed that the fact he’s a quarter of the ladies’ size created insuperable, er, logistical problems (we often we find him flailing on his back, because they’ve tired of his squeaking, humping antics and flipped him). The other is larger, but lower-key: he likes being alone and chomping dandelions (I know who I’d rather was the daddy).

My husband puts the eggs in a homemade incubator anyway, just in case, and last week bolted out of the garage in wide-eyed panic shouting: “Baby!” I have never moved faster. If you’re wondering what 17 grams of tortoise looks like, it’s basically a ping-pong ball. A grumpy, yawning, tortoiseshell ping-pong ball, contemplating us with unimpressed, sesame-seed-sized eyes. We stared back, literally shell-shocked.

So, 20 years on, we’re incompetent new parents again and it’s even more terrifying than when our sons were born. We couldn’t persuade baby to eat for the first day and Google was no help. Reptiles are like houseplants: whatever ails them is too much or too little of something (water, light, minerals), but no one can ever tell you which, and my track record with houseplants is not encouraging. Worse, the tortoise versions of Mumsnet are angry, confusing places: whatever you’re doing is definitely wrong, probably fatal and someone will tell you IN CAPS.

We hit three pet shops in one fraught afternoon for kit no one agreed on. We panic bought two separate lamps and a tray, which we deep-filled with panic-bought coconut coir substrate that a bare majority of vehemently opinionated reptile forum posters recommended. We created a forest of chicory seedlings for baby to browse, and filled a dish with tender foraged leaves and other forum-approved (yet simultaneously FATAL) foods. Then we bathed it in an ice-cream tub (daily baths are either essential or excessive; whichever you choose is wrong) and settled in for a lifetime of worry.

Because this tortoise is, and I say this with love, the dumbest animal I have ever tended. I spent 15 minutes watching it try to eat a slate on Thursday. An actual slate. Then it got exhausted and had a long nap. My husband woke at 4am worrying he’d seen it eat grit. “Maybe that’s what it does in the wild?” I said as we tweezered grit fragments (from the chicory seedlings) out of the vivarium. “Maybe they try everything, to learn what’s edible?” “In the wild, most hatchlings would die,” he replied, flatly.

It’s still alive, so far, but we’re hollowed out – deranged with anxiety and hours of staring. “Back off!” I snap, as my husband hovers. Whenever the baby sees us, it pretends to be a pebble: a good survival strategy, but agonising for two home-working helicopter parents with nothing better to do than lurk, radiating terrified love. My husband uses a meat thermometer to probe the vivarium substrate temperature and grates cuttlebone over leaves for calcium; he’s installed two motion-activated cameras to monitor baby’s movements if we ever go out (we don’t). I’ve been tweezering shoots, grating cucumber and creating frisée chiffonade for its delectation like Carmy from The Bear . I stare rapt at its adorable mini claws and dinky neck wrinkles as it marches unsteadily through food it’s supposed to be eating. I spam its human siblings endlessly with footage of it yawning, or eating soil.

Our sons are involved whether they like it or not: Hermann’s tortoises can live to anything from 50 to 100 years, so assuming baby gets less stupid eventually, it will outlive us (and unlike them, never leave). I must update my will. In the meantime, we’re besotted, obsessed, and petrified we’ll somehow kill our beloved. It’s just like 20 years ago.

• Emma Beddington is a Guardian columnist