Jumping spiders eat other invertebrates. Live ones. That's the non-negotiable part of keeping them, and it's the bit that puts some people off. If you aren't comfortable keeping cultures of flies in your home and dropping them into a small box to be stalked and pounced on, jumping spiders probably aren't for you. But if that sounds like interesting natural behaviour to watch (and it is, genuinely), then feeding is one of the most rewarding parts of keeping these animals.
Why live prey only
Jumping spiders are active visual hunters. They belong to the family Salticidae, and their hunting strategy relies on their exceptional eyesight to locate prey, their ability to plan an approach (they'll sometimes take circuitous routes to ambush from behind), and a final pounce. This entire sequence is triggered by movement. A dead fly on the substrate holds zero interest for a jumping spider. They won't scavenge, and they won't eat pre-killed food.
This isn't a quirk you can train out of them. It's fundamental to how they perceive and interact with the world. Their anterior median eyes (the big forward-facing pair) have tube-shaped retinae that can resolve fine detail and track moving objects. The hunting response is visual and movement-dependent. No movement, no hunt.
Fruit flies: the staple for small spiders
Drosophila melanogaster (small fruit flies) and Drosophila hydei (larger fruit flies) are the foundation of feeding for slings and juveniles. Flightless or curly-wing variants are sold specifically for this purpose, and they're much easier to work with than wild-type flies that go everywhere the moment you open the culture.
D. melanogaster is the smaller of the two (about 2mm) and suitable for very young slings. D. hydei is larger (about 3-4mm) and works well for slightly bigger juveniles. Both are sold in culture pots that produce flies continuously for several weeks if kept at room temperature. You tap a few out into the spider's enclosure and let nature take its course.
Keeping fruit fly cultures going is simple. Buy a new culture every few weeks, or make your own medium (there are recipes all over hobbyist forums, usually involving some combination of mashed potato, sugar, yeast, and vinegar). A culture produces flies for roughly 3-4 weeks before petering out.
Graduating to bigger prey
As your spider grows, it'll need larger food. The transition usually goes from fruit flies to houseflies, greenbottles, or bluebottles. You can buy these as pupae (sometimes called "casters" in fishing circles) from livefood suppliers or fishing bait shops. The pupae are stored in the fridge to slow development, then taken out a few at a time. They hatch into adult flies within a day or two at room temperature.
Houseflies (Musca domestica) are a good all-round feeder for adult jumping spiders. They're the right size for most Phidippus species and they're active enough to trigger hunting behaviour without being so fast that the spider can't catch them. Greenbottles and bluebottles are slightly larger and work well for bigger species or particularly hungry adults.
Small crickets (1st or 2nd instar) are sometimes used as feeders. They work, but I prefer flies for a few reasons. Crickets can hide in the enclosure and are harder to remove if uneaten. They can also harass a moulting spider if left in overnight, which can cause injury. Flies tend to move around more visibly and are easier for the spider to catch.
Other feeder options
Waxworms (the larvae of Galleria mellonella) are accepted by larger jumping spiders. They're soft, nutritious, and slow-moving. The downside is they're fatty, so they should be an occasional treat rather than a regular meal. Think of them as the chips of the spider feeder world.
Mealworms are sometimes offered but they're not ideal. Their hard exoskeleton makes them difficult for jumping spiders to process, and they can burrow into substrate and hide. Small mealworms are acceptable in a pinch but aren't a go-to feeder.
Some keepers have had success with bean weevils (Callosobruchus maculatus) as an intermediate size between fruit flies and houseflies. They're easy to culture and about the right size for juvenile spiders transitioning off fruit flies. Worth trying if you can get a culture started.
How often to feed
Juveniles: every 2-3 days. They're growing and moulting frequently, so they need regular meals to support that. A juvenile P. regius might eat 3-5 fruit flies in a sitting.
Adults: every 3-5 days. They need less food per unit of body mass than growing juveniles, and overfeeding isn't great for them. An adult P. regius might eat one or two houseflies per feeding.
If the spider's abdomen is very round and taut, ease off on feeding. If it looks small and somewhat shrivelled relative to the cephalothorax (the front body section), feed more frequently and check your misting routine because dehydration can be a factor too.
When they won't eat
Jumping spiders refuse food before a moult. This can last anywhere from a few days to over a week. The spider will retreat into its web sac and sit there, looking (from the outside) like it's dead or dying. This is normal. Don't panic, don't poke the web sac, don't try to force-feed. Just wait. Once the moult is complete and the new exoskeleton has hardened (give it a full day after the spider emerges), you can offer food again.
Spiders also sometimes refuse food if the prey is too large or too small. An adult P. regius might ignore a single fruit fly because it's not worth the effort. A juvenile might back away from a cricket that's almost as big as it is. Matching prey size to spider size is part of the learning curve, and you'll get a feel for it fairly quickly.
Cooler temperatures also suppress appetite. A spider kept at 18C will eat less frequently than one at 24C. This is normal metabolic slowing, not a health problem.
Storing feeders
Fruit fly cultures live on a shelf at room temperature. Fly pupae go in the fridge and come out a few at a time. Crickets need their own small container with food and water gel (a dry cricket is a dead cricket within hours). Keeping feeders alive and healthy is a minor ongoing task that's easy to forget about until you open the fridge and realise everything's hatched or died.
Budget for feeders as a recurring cost. It's not expensive (a few pounds a month for a single spider), but it's not zero either. Factor it in before you buy your first spider.