Updated: May 17, 2020
What size of bugs to feed jumping spiders and how often to feed
My rule of thumb is to match prey size to the size of the spider's head, abdomen, or the full length of their body, depending on the life stage, condition, and courage of the spider.
I try to feed a growing juvenile as big a prey they will take down, every day. Sometimes, right after a molt, and even after an adult molt, they are more timid and won't take down larger prey. I will try smaller prey to stimulate their appetite first, then feed them larger ones as they have exercised those hunting "muscles" again.
With adult males, I will feed them a prey size the size of their head, abdomen, or full-length of body, depending on what they will take, right after their molt to fatten them up from the ordeal of premolt and molting for a few consecutive days. Then, I can feed prey that are the size of their head or abdomen every 3 days.
With adult females, I feed a prey the size of their body until they are plump, and taper off to feeding every 3 days, until they lay eggs. At which point, the female is very skinny and needs more nourishment again.
What to feed a jumping spider
The best types of prey items for spiderlings - young juveniles:
melanogaster fruit flies
hydei fruit flies
false stable flies
1 week crickets
The best types of prey items for older juveniles - adults:
false stable flies
blue bottle flies
blue bottle fly spikes
wax moths that come from wax worms
size appropriate mealworms (about length of spider)
size appropriate crickets (size of spider's head, abdomen, or length of their body)
DO NOT FEED:
any other predatory bug
general rule of thumb is not to feed anything wildcaught
Troubleshooting a spider that isn't eating
An adult jumping spider may not eat very much after they've regained nourishment after molting. Males' metabolism slow down very fast after reaching maturity. They may not eat more than a prey every 3 days to once every week, depending on the size of the prey. If the spider acts healthy (has a nest, moves normally, abdomen is taut without wrinkles), then the adult male just simply isn't hungry.
An adult female will eat quite often after a molt to make eggs (even if infertile) inside their abdomen. They will/should be fed every day until they are plump. And then you can taper off to feeding a larger prey every 3 days. However, once they lay eggs, they will need daily nourishment again. With a female on eggs, they may not come out to hunt until their spiderlings have dispersed, which can take up to a month or more. If you can see them through the nest, and they seem very skinny, but won't come out to hunt, try tweezering a blue bottle or house fly into their nest for them to take.
After an adult female is done laying eggs for good (fertile, or infertile), they will stop eating very much at all. They may only be interested in a small prey every few days or once every week. This is normal. I will offer water more often at this point, when they refuse food.
If a juvenile is not eating and getting thin, I take action immediately. I give a juvenile up to 2-3 days after a molt to eat by themselves. If they are not eating, I will try different things to stimulate appetite.
How to stimulate a jumping spider's appetite
Make sure their enclosure isn't too wet; that means NO condensation. Add warmth and light. I have a heat mat hooked up to a thermostat set at about 80F. I use a regular LED bulb lamp for light, but they also get indirect sunlight. If a spider is not eating, make sure to give them some natural light, but not direct sunlight as they can overheat from it very easily.
If that doesn't work, try a variety of prey. Flies the size of the spider's head are often a good choice for a timid spider that is not eating. Otherwise, they sometimes will take an active cricket. Something about the flutter and hopping that stimulate their appetites. Make sure the spider is in a smaller enclosure to be able to see and easily catch the prey without too much active hunting needed.
Force-feeding a jumping spider
My last resort is force-feeding. I will cut open a waxworm or a mealworm, squeeze out the guts, and use my tweezers to dab it onto the spider's mouthparts. Some spiders will actually eat it happily. For others, it may take awhile, and the spider will resist. Be gentle but persistent. Otherwise, another way is to stick it onto the spider's face and have them groom it off. If the spider is healthy, and will eventually pull out of it, this drastic measure does the trick, and they start eating by themselves after a few feedings.