One of the genuine advantages of keeping invertebrates over most other pets is cost. You're not paying for vet bills, vaccinations, or commercial pet food. But "cheap" is relative, and costs vary a lot depending on what you keep. Here's an honest breakdown.
Startup costs
The initial outlay covers the enclosure, substrate, heating (if needed), and the animals themselves.
Budget setup: isopods or stick insects
- Plastic tub with drilled ventilation: 3-5 quid
- Organic topsoil, sphagnum moss, leaf litter: 5-10 quid (enough for several enclosures)
- Cuttlebone for calcium: 1-2 quid
- Spray bottle: 1 quid
- Digital thermometer/hygrometer: 5-8 quid
- Starter colony of Porcellio scaber or Armadillidium vulgare (10-15 individuals): 5-15 quid
Total: roughly 20-40 quid. You could do it for less if you forage your own leaf litter (oak and beech are fine) and already have a suitable container. Stick insects are similar: the main ongoing cost is fresh bramble leaves, which grow wild everywhere.
Mid-range setup: flower beetles or jumping spiders
- Enclosure (acrylic box for spiders, plastic tub for beetles): 8-20 quid
- Substrate (fermented flake soil for beetle larvae, coco fibre for spiders): 5-15 quid
- Heat mat and thermostat (if needed): 15-25 quid
- Digital thermometer/hygrometer: 5-8 quid
- Cork bark, branches, decor: 5-10 quid
- Pachnoda marginata larvae (3-5): 8-15 quid
- Phidippus regius (1 juvenile): 15-30 quid
- Fruit fly culture for spider: 5-8 quid
Total: roughly 50-100 quid depending on what you already have. The heat mat and thermostat are the biggest single cost, and you'll reuse them across setups.
Higher-end setup: giant millipedes
- Larger enclosure (glass terrarium or big plastic tub): 15-40 quid
- Substrate (topsoil, rotting hardwood, leaf litter, sphagnum, calcium source): 15-25 quid
- Heat mat and thermostat: 15-25 quid
- Cork bark and decor: 5-10 quid
- Archispirostreptus gigas (1 adult): 15-35 quid
Total: roughly 65-135 quid. The substrate for millipedes is bulkier because they need deep bedding (10-15cm minimum) and the enclosure has to be large enough for an animal that can reach 30cm.
Ongoing costs
This is where invertebrates pull ahead of almost every other pet. Monthly running costs are minimal for most species.
Isopods and millipedes
Close to zero once established. They eat their substrate, leaf litter you can collect for free, and vegetable scraps from your kitchen. You'll occasionally need to top up substrate, buy more cuttlebone, or replace sphagnum moss. Maybe 2-5 quid a month at most, and some months nothing at all.
Beetles
Larvae eat substrate, which you'll need to top up or replace as they consume it. Fermented flake soil costs around 5-10 quid per litre depending on the supplier. A single Pachnoda larva might go through 1-2 litres over its development. Adults eat fruit (pennies) and beetle jelly (a few quid for a pack that lasts weeks). Ongoing costs are low, maybe 5-10 quid a month if you're running a breeding group.
Jumping spiders
The main ongoing cost is feeder insects. A fruit fly culture costs 5-8 quid and produces flies for several weeks. You might need a fresh culture every 3-4 weeks. For adult spiders eating larger prey, a tub of house flies or crickets runs similar amounts. Call it 5-10 quid a month.
Mantids
Similar to spiders: live feeder insects are the main cost. Fruit flies for nymphs, larger flies and crickets for adults. Around 5-10 quid a month. Mantids have relatively short lifespans (6-12 months for most commonly kept species), so costs are time-limited.
Electricity
If you're running heat mats, factor in a small amount for electricity. A typical reptile heat mat draws 5-14 watts. Running one 24/7 costs about 1-3 quid a month at current UK electricity rates. Not nothing, but not a lot. Multiple enclosures in a warm room can sometimes share heat from a single mat or from ambient room heating.
The expensive bits
Some species and some aspects of the hobby cost noticeably more:
- Cubaris isopods (Rubber Ducky, Panda King): individual animals can cost 5-20 quid each, and you need a starter group. These are slow breeders, so replacing losses is painful.
- Large rhinoceros beetle larvae: species like Dynastes hercules cost 20-50 quid per larva and need premium flake soil for over a year.
- Rare jumping spider morphs or species: 30-60 quid for a single juvenile.
- Glass terrariums with front-opening doors: 40-80 quid depending on size. Functional, but you can get the same results from a plastic tub for a fraction of the price.
Hidden costs to think about
- Replacement cultures of feeder insects if yours crash (fruit fly cultures sometimes fail)
- Postage on online orders, which often adds 4-7 quid per delivery
- Expansion. This hobby creeps. You start with one tub of isopods and end up with a shelf of twenty enclosures. Budget accordingly, or accept the inevitable.
Compared to other pets
A dog costs an average of 1,500-2,000 quid per year in the UK. A cat runs about 1,000. Even a hamster costs 400-500 a year once you include bedding, food, and vet bills. A colony of Porcellio scaber costs maybe 50 quid total to set up and under 30 quid a year to run. The comparison isn't really close.
The caveat is that this only holds if you have self-control. Plenty of keepers spend hundreds of pounds a year on new species, better enclosures, and premium substrates because they enjoy it. The hobby is cheap if you want it to be. It's also very easy to spend money on if the collecting bug bites.