Feeding Isopods to Tarantulas and Slings

Quick answer

Dwarf white isopods work well as a feeder for tarantula slings and small juveniles, and reasonably well for larger spiders as a supplementary item rather than a staple. Their real advantages over pinhead crickets are not nutritional: they are that a stray isopod cannot hurt a moulting tarantula, that they do not smell, and that a culture keeps producing instead of needing reordering. Their real limitation is that they burrow, so a spider that hunts by ambush at the surface may simply never meet them.

Where this comes from

We keep tarantulas as well as selling isopods, and this article started with nine spiderlings out of a mystery box. Rather than run a pinhead cricket culture alongside everything else, we tried feeding them dwarf white isopods instead. The slings took them without hesitation.

The part that was not expected: several larger tarantulas, animals that would normally be moved up to the next feeder size, kept taking dwarf whites anyway. That is worth saying plainly, because the standard feeder-sizing advice implies a fairly narrow window in which each prey item is useful, and in practice the window for isopods runs wider at the top than the charts suggest. It means one culture covers more of a mixed collection than you would plan for.

This is our own observation across our own shelves rather than anything measured. We would rather label it that way than dress it up.

The moulting argument, which is the one that matters

A tarantula in moult is helpless. It is soft, it cannot right itself quickly, and it cannot defend itself for hours or in some cases days. A cricket left in the enclosure during that window is a genuine hazard: crickets are omnivorous, they chew, and a hungry one will start on a soft spider. Keepers lose animals this way every year, and the standard advice to remove uneaten crickets exists precisely because of it.

Isopods do not present that risk. They are detritivores with mouthparts built for rotting leaf litter, and they have no interest in a living animal, moulting or otherwise. If a dwarf white is still in the enclosure a week later it has been quietly eating waste and mould the whole time.

That is the single strongest reason to use them, and it applies whether or not you care about any of the others.

Cleaner, in a way that compounds

Anyone who has run a cricket bin knows the smell. Crickets die in transit, die in the tub, and the ammonia from decomposition is unmistakable within a few days. They also escape, and an escaped cricket chirps behind a skirting board for a fortnight.

Isopods do none of that. There is no noise, effectively no odour from a healthy culture, and an escapee is a woodlouse in a house that almost certainly already has woodlice in it. More usefully, uneaten isopods do not become a waste problem in the spider's enclosure. They become part of the clean-up crew, working through boluses and any mould starting on the substrate. You are not just feeding the tarantula, you are seeding the enclosure.

The cost argument, stated honestly

A cricket order is a consumable. You buy it, some of it dies, you use the rest, you order again. That cycle continues for as long as you keep the animal.

An isopod culture is a one-off purchase that then reproduces. Dwarf whites in particular are parthenogenetic, meaning every animal in the culture is female and produces young without mating, so there is no sex ratio to get wrong and no way to buy a group that turns out not to breed. Given warmth, damp substrate and something to eat, the culture becomes self-replacing and you harvest from it indefinitely.

We have deliberately not put figures on this, because feeder prices move and it would be a made-up comparison by next season. The structural point stands on its own: one purchase that reproduces against a repeat order that does not.

Which species, and for what size of spider

Dwarf whites (Trichorhina tomentosa)

The default. Adults run 2 to 4 mm, which suits slings from the first proper feed onwards, and they breed fast enough to keep up with a modest collection. They are also blind, slow and soft-bodied, so nothing about them stresses a small spider. Full husbandry is in our dwarf white isopod care guide.

Powder orange and powder blue (Porcellionides pruinosus)

Noticeably bigger at around 10 to 12 mm and much faster moving, which makes them a better match for juvenile and adult spiders that want prey they can chase. They also breed quickly, which matters if you are feeding more than a few animals.

What not to use

Anything expensive, anything slow-breeding, and anything with a hard shell relative to the spider's size. Premium Cubaris are not feeders under any circumstances, and armoured conglobating species like larger Armadillidium are poor value as food because a spider gets very little for the effort.

The honest limits

• They burrow. This is the big one. Isopods head for cover, and a terrestrial ambush hunter sitting at the mouth of a burrow may never encounter one. Offering them on the surface near the spider, or in a shallow dish, works better than tipping them in and hoping.
• They are not a complete diet for larger spiders. As a supplementary item and a clean-up crew, excellent. As the only food for an adult terrestrial, no. Larger tarantulas need prey with more mass than a 3 mm isopod can provide, whatever quantity you offer.
• Production has a ceiling. A dwarf white culture is self-sustaining but not fast on the scale of a large collection. If you are feeding twenty spiders you will need several tubs running in rotation, started well before you need them.
• Nutritional data is thin. There is very little published analysis of isopods as prey, and what exists is mostly on calcium content rather than a full profile. Anyone quoting you precise macronutrient ratios for feeder isopods is extrapolating.

Setting up a feeder culture

Keep it simple and keep it separate from any display colony. A lidded tub with a few small vents, five to eight centimetres of coconut fibre and leaf litter, a piece of cork bark to lift for harvesting, and a permanent calcium source. Dwarf whites want it consistently damp and reasonably warm; drying out is the one thing that reliably kills a culture. Feed them the same things you would feed any isopod, with a little more protein than a display colony gets, since you are harvesting biomass out of the system rather than letting it accumulate.

Harvest by lifting the bark and tapping animals into a pot. Take from the culture no faster than it is replacing itself, and start a second tub as insurance before you need it.

If you want the wider picture on using invertebrates as food, our guides to isopods as feeders for reptiles and amphibians and springtails as feeders for micro-pets cover the other end of the size range. For a general-purpose setup that doubles as a clean-up crew rather than a dedicated feeder tub, see our guide to building a bioactive terrarium.

Frequently asked questions

Can isopods hurt a tarantula?

No. They are detritivores and have no mouthparts capable of injuring a living spider, including one that is mid-moult. This is the main reason to prefer them to crickets, which genuinely can.

Will a tarantula eat isopods?

Most will, and slings almost always do. Some individuals ignore them, usually because the isopods burrow before the spider notices. Offering them near the spider rather than at the far end of the enclosure fixes most refusals.

Are dwarf whites big enough for an adult tarantula?

Not as a staple. At 2 to 4 mm they are a supplement for a full-grown terrestrial, though we have repeatedly seen larger spiders take them when offered. Powder species are a better fit at that size.

Do I need to gut-load them?

Not in the way you would a cricket. An isopod culture fed on leaf litter, rotting wood and occasional protein is already eating a varied diet continuously, so what you put into the culture is what the spider gets. Feeding the culture well a day or two before harvesting is worth doing.

Can I just put isopods in the tarantula enclosure permanently?

Yes, and many keepers do. A resident clean-up crew deals with boluses and mould, and the spider takes one occasionally. Be aware you are then running a colony in a container that is not set up for one, so numbers may stay low.