Last week, a store manager at a Whole Foods in Tulsa, Okla., was surprised—to say the least—to find a large brown spider lurking in a bunch of bananas. The spider was initially identified as a Brazilian wandering spider,  a menacing-looking creature with furry fangs and legs as long as five inches (12.5 centimeters) that is considered to be one of the world's most venomous spiders, and one of the few that can kill humans. (Luckily, an anti-venom to the Brazilian’s bite was developed in 1996.)

According to the Tulsa World, two local entomologists in the end determined that the invader was more likely a huntsman spider, which is large and brownish in color like the Brazilian wandering, but is nontoxic to humans.

Each year, there are several news reports of wandering and huntsman spiders, the main "banana spiders," showing up in grocery store bananas as well as poisonous black widows, which find their way into bunches of grapes on store shelves. Both fruits are generally sprayed with pesticides to prevent insect infestation and usually washed before shipment. Still, even with these precautions and visual inspections, some insects manage to survive.

What draws spiders to bananas and grapes—and what should consumers and produce workers who find the potentially deadly critters in their fruit do?

To find out, we spoke with Linda Rayor, a spider expert and senior research associate  in Cornell University's entomology department.

[An edited transcript of the interview follows.]

How common is it to find a spider in grocery store fruit—and are spiders more common in grapes and bananas from certain regions?
For the bananas, you have a reasonable chance of getting them in ones imported from anywhere in Central or South America, the main sources of the fruit. I have no idea of the actual risk, but there are different types of wandering and huntsman spiders throughout Latin America. You pretty much have a chance of getting black widows—which are found all over the world—in grapes anywhere they grow.

Is there something else about grapes that black widows find especially appealing?
Spiders are going to be found anywhere that there are insects for them to eat—and there are plenty of insects on grapes. They're very common in vineyards around the world. Grape arbors (the supports between grapevines) provide really great support systems for spider webs—they're perfect for cobweb-building spiders like the black widow—and the grapes make great hiding places. (Black widow bites can be toxic to humans, but they’re not nearly as dangerous as those from the most poisonous wandering spiders. They can cause intense pain and shortness of breath, but are rarely lethal in healthy adults.)

How about bananas?

Banana trees have these tightly coiled leaves coming up, and then the banana flowers lean down over that. Well, these banana leaves turn out to be just dandy places for these spiders to live, especially ones that hang out on the leaves. The leaves have this kind of hollow center, so a lot of the spiders hang out in the central, deep-covered hole during the day and then come out at night to hunt on the outside of the leaf. Neither one of them are web-building spiders, and so they just kind of hang out on the leaves at night and nab things that wander or fly by.

There are two common groups that are both referred to as "banana spiders," but they're totally different from one another. The first group is the wandering spiders, which is the family Ctenidae, or ctenids. The other is an entirely different family, the Sparassidae, which are the huntsman spiders. They're both big spiders that have relatively long legs. They can both easily be the size of the palm of your hand, no problem.

Is there an easy way to tell the two types of banana spiders apart?
In one description of the spider in Tulsa, the store manager said it jumped at him. That is so much more like wandering than the huntsman spiders. Huntsmans back off and then run away sideways really fast. They're fast, but they're not aggressive.

Huntsmans are big enough [for their bites] to break the skin. I've probably been bitten by huntsmans—I work with Australian huntsman spiders—I don't know, five times? It hurts because it breaks the skin, but their venom is really nothing much, and they're not really inclined to bite at all. When a wandering spider is threatened, though, it tends to rear up so its front legs go up in the air in a pretty feisty way, often with its fangs open. It's really scary. So, you've got very, very different behaviors.

The huntsman spiders are also different in appearance. Most spiders stand up on all eight legs, but the huntsman spider's legs are rotated so that they're horizontal to the body. This allows them to get really flat to the ground and to move sideways really effectively. In fact, in the U.S. they're sometimes called "giant crab spiders," because they can scuttle around like crabs. The wandering spiders have normal legs that aren't rotated like the huntsman spiders' legs, so they're clearly standing upright, and the underside of the wanderings' front legs, at least in some of their species, is often brightly colored in reds or yellows. It's a warning coloration.

What should consumers do if they encounter one of these spiders in their fruit?
It's like anything: you have to pay attention to what you're doing and make sure you rinse off your fruit. The wandering and huntsman spiders are both pretty big, so you wouldn't miss them.

Black widows are much easier to miss, because they're about the size of a grape. Black widows are really fast in webs, but they're pretty inadequate on the ground. They really can't run on the ground at all. Their abdomens are just too big, so they kind of waddle around. So a black widow is more inclined to simply drop off the web or off a grape into, say, your sink. And then, once on the ground, it's not going anywhere fast.

Wandering spiders and huntsman spiders are really fast, and they do just fine on the ground. Now, I'm personally not all that big on squishing these guys. I think it's a whole lot more interesting to get them in a jar and get them identified. Spiders don’t naturally attack humans, so the risk of getting bitten is very low. Basically, people shouldn’t worry too much. Black widows, for example, are really shy. They only bite when they perceive a threat, such as a hand trying to grab them. You should try to get the offending spider to drop on the ground and quickly scoop it up into a large container (just as you would with any other spider).

If a black widow does bite you, wait 15 minutes to see if she (only the females are toxic enough to harm humans) has actually injected venom in you--it starts to really hurt.  That is the advice given by Poison Control in Arizona.  Then go to an emergency room where they can provide antivenom or palliative treatment. Evidently, when a Brazilian wandering spider bites, it hurts immediately, so you go to the doctor or emergency room with the spider if possible,  It’s always best for people to bring the spider with them, so the hospital can provide the correct treatment. (For more tips see the CDC’s guide on venomous spiders.)

Could stores or shippers do more to keep spiders out of our bananas and grapes?

I'm not sure what more could be done. A lot of the insects on these fruits are being doused with chemicals or washed before shipping. For example, before bananas are shipped, they are taken off the plant, put in a water trough to wash them off and then they're packed in large shipping containers, which are kept quite cool. Grapes are shipped at cooler temperatures, too.

What will happen is that the spiders at those lower temperatures become quiescent. Some may be dying, but a lot of animals can take cold temperatures for awhile. Both bananas and grapes are sold at the grocery not chilled. So, basically, what you've got is spiders that have been cooled pretty much until they've reached the grocery that are waking up.

How dangerous are most spiders?
What's important to keep in mind is that truly a small portion of spiders are dangerous to humans. Basically, most spiders can't do a whole lot. They can't break the skin or their venom doesn't react with human physiology. It's estimated that 50 percent of all spider bites don't even inject venom, and they are unlikely to go after humans. Still, you wouldn't want to be bitten by a wandering spider, Brazilian or otherwise. There are wandering spiders all over Latin America, where most bananas come from, the Brazilian wandering spider, or Phoneutria nigriventer, is only found on the Atlantic coast of Brazil, not in Honduras, where the bananas at the Tulsa store came from. The chances of encountering one are really very slim.