You’ve probably done it. Most of us have. You find a big, hairy wolf spider scurrying across the linoleum or a delicate cellar spider vibrating in the corner of the garage, and your first instinct is to grab a Mason jar. You poke some holes in the lid with a hammer and a nail, toss in a dry leaf, and suddenly you have a front-row seat to one of nature’s most misunderstood predators. But keeping spiders in a jar isn't just a simple childhood hobby; it’s a tiny, high-stakes ecological experiment that usually ends poorly for the eight-legged guest if you aren't careful.
Most people think a jar is a safe microcosm. It isn't.
If you don't understand the physiology of the specific arachnid you've trapped, that glass enclosure becomes a death trap within forty-eight hours. Spiders are incredibly sensitive to humidity and airflow. Those holes you poked in the metal lid? They might be enough for a human to breathe, but they often create a drafty, desiccating environment that dries out a spider’s book lungs—the specialized respiratory organs they use to pull oxygen from the air. Or, conversely, if the jar stays too moist, you’re basically inviting a fungal infection that will consume the spider from the inside out.
The Problem With Modern Glass Enclosures
We see these "nature jars" all over social media. They look aesthetic. They look educational. But glass is a terrible thermal conductor for a creature that can't regulate its own body temperature. If you leave a jar near a window, the greenhouse effect kicks in faster than you’d think. A spider trapped in a glass jar on a sunny windowsill can literally cook in minutes.
It’s honestly kind of heartbreaking.
I've talked to hobbyists like those in the American Tarantula Society who emphasize that even "true spiders"—the ones we find in our houses—require specific environmental gradients. You can't just put a jumping spider in a jam jar and expect it to thrive. They need vertical space. They need cross-ventilation. Most importantly, they need a substrate that holds a very specific amount of moisture. Without a layer of peat moss or coco fiber, a spider in a jar is basically living on a cold, hard, slippery floor where it can't even get a decent grip to hunt.
Can Spiders Actually Live Together?
One of the most common questions people ask when they start putting spiders in a jar is whether they can give their pet a "friend."
Don't. Just don't.
🔗 Read more: How to Repair Chips in Ceramic Floor Tiles Without Replacing the Whole Floor
With very few exceptions—like the Anelosimus eximius, a social spider found in South America—spiders are aggressively solitary. If you put two spiders in a jar, you aren't starting a colony; you’re setting up a gladiatorial arena. One will eat the other. It might happen in five minutes, or it might happen at night while you’re sleeping, but cannibalism is a primary survival strategy for many species. Even during mating, the female often consumes the male because he represents a high-protein meal that will help her produce healthier eggs.
It’s brutal. But that’s biology.
The Ethics of Temporary Captivity
Is it okay to keep a spider for a few days to show the kids? Probably. But you have to know when to let go. Dr. Linda Rayor, a noted arachnologist at Cornell University, has often pointed out how fascinating these creatures are for study, but she also highlights the complexity of their needs. A spider’s life revolves around its web or its hunting territory. When you remove it, you disrupt its ability to feed and reproduce.
If you're going to keep spiders in a jar for observation, you need to follow a strict protocol to ensure you aren't just killing a beneficial predator that would otherwise be eating the flies and mosquitoes in your yard.
- Ventilation is everything. Use a fine mesh or fabric secured with a rubber band instead of a poked-hole metal lid. This allows for actual air exchange.
- Hydration, not drowning. A spider doesn't need a bowl of water. It needs a tiny bit of damp cotton or a light misting on one side of the glass. If the spider falls into a water dish, the surface tension will often trap it and drown it.
- The "Two-Day Rule." Honestly, unless you are prepared to build a full terrarium with lighting and live prey, don't keep a wild spider for more than 48 hours. Take your photos, watch it move, and then let it go exactly where you found it.
Why "The Jar" Fails the Jumping Spider
Jumping spiders (family Salticidae) are the "gateway drug" of the spider world. They’re cute. They have those massive anterior median eyes that make them look like Pixar characters. They’re also incredibly smart. Research has shown they can plan routes and recognize prey from a distance.
Putting a jumping spider in a small jar is like putting a border collie in a closet.
These spiders are active hunters. They need space to jump and explore. In a small jar, they often become lethargic. They stop eating. They might even stop grooming themselves. If you want to observe a jumping spider, use a large, clear plastic container (at least a gallon in size) and add sticks, silk plants, and places to hide.
Feeding Your Captive Spider
This is where it gets messy. You can't just give a spider a piece of ham. They are insectivores. They need movement to trigger their hunting instinct. If you have a spider in a jar, you’re going to have to find live flies, small crickets, or moths.
💡 You might also like: Why Coconut Lip Gloss is Actually Better for Your Skin Than Traditional Formulas
But here’s the kicker: wild-caught insects might have been exposed to pesticides.
If you feed your jarred spider a fly that just walked through a puddle of RoundUp, you’re going to kill your spider. Professional keepers buy "feeder insects" from pet stores because they know those bugs are clean. If you're just doing this as a hobby in your kitchen, you’re taking a massive risk every time you drop a random backyard bug into that jar.
Humidity and the Molting Process
Spiders don't grow like we do. They have to shed their entire skin—the exoskeleton—to get bigger. This process, called molting, is the most dangerous time in a spider’s life. If the humidity in your jar isn't perfect, the spider can get stuck in its old skin. This is called a "wet molt" or a "bad molt," and it's almost always fatal.
Inside a glass jar, the air is often too dry. The spider begins to pull itself out of the old shell, but the tissue dries and hardens before the process is finished. The spider ends up deformed or paralyzed. It’s a slow, ugly way to go.
Better Alternatives for Nature Lovers
Instead of the jar method, consider "field observation."
Get a good macro lens for your phone. Go outside at night with a headlamp. If you hold the light at eye level, you’ll see the "eye shine" of wolf spiders reflecting back at you from the grass. It looks like tiny diamonds scattered in the lawn. This allows you to see their natural behavior—hunting, mating, and interacting with the environment—without the stress and mortality risk of a glass enclosure.
If you absolutely must keep one, invest in a "Kritter Keeper" or a specialized acrylic enclosure. These are designed with the ventilation and access points that a standard Mason jar lacks.
👉 See also: Bailey Brewer Trailer Hitch: Why Most People Get It Wrong
Actionable Steps for Responsible Observation
- Identify before you catch. Use an app like iNaturalist or Seek to make sure you aren't handling a medically significant spider like a Brown Recluse or a Black Widow.
- Use "Catch and Release" containers. There are specific tools available that allow you to trap a spider against a wall and slide a door shut without touching the animal or damaging its legs.
- Prioritize darkness. Spiders are generally nocturnal or crepuscular. If you keep them in a jar, put a piece of cardboard around it so they feel secure. Constant light is stressful for them.
- Release at night. When you’re done observing, let the spider go at dusk. This gives them the best chance to find a new hiding spot before birds and other daytime predators spot them.
- Clean your gear. If a spider dies in a jar, don't just rinse it out. Use a mild bleach solution to kill any lingering parasites or fungi before using that container for anything else.
Keeping spiders in a jar can be a great way to spark a lifelong interest in entomology, but it’s a responsibility that shouldn't be taken lightly. Respect the creature enough to provide more than just a glass tomb. These animals have been around for over 300 million years; they deserve better than a dusty jar on a shelf.