Identifying a spider in my garden
September 16, 2019 10:04 PM   Subscribe

This attractive lady appeared on my arm when I was doing some yard work. I put her on some wire netting so I could get some pictures, but the light wasn't very good. She has the body shape of one of the widow family, but the belly doesn't have the orange/yellow of a black or brown widow. [Album link, in case urls don't work]

Unfortunately, I didn't get a good shot of the top of her body, but there's a stripe across the front of her abdomen, and I'd say she was more nickel to quarter size than penny sized, a quite substantial spider. I am wondering if she could be a false black widow, Steatoda grossa, or one of the relatives. This was in San Jose, California.
posted by tavella to Science & Nature (16 answers total) 1 user marked this as a favorite
The reason I'm not sure about it being grossa is that I didn't notice any skull or other significant strong markings on her back when she was on my arm, she was mostly dark all over.
posted by tavella at 10:18 PM on September 16, 2019

None of your images are loading for me I’m afraid...
posted by Homo neanderthalensis at 10:54 PM on September 16, 2019 [6 favorites]

First, thanks for being a friend to spiders. Most people needlessly fear and kill them, never realizing how much they do to keep insect populations in check and maintain healthy local ecosystems.

A light gray band across the abdomen's dorsoanterior margin, along with similarly colored stripe along the midline, is the hallmark of the female false black widow. In the western black widow, which is the only other California spider with a gray band across the front of the abdomen, this midline stripe is always red.

(I had no problem loading your images)
posted by BadgerDoctor at 11:04 PM on September 16, 2019 [6 favorites]

Hmm! Okay, I tried making an album of all the photos, does this work?
posted by tavella at 11:32 PM on September 16, 2019

I have no idea what kind of spider it is, but just wanted to say: album works for me, original links did not. I'm in the US, using Windows and Chrome.
posted by nirblegee at 12:23 AM on September 17, 2019

[I've added the album link to the above-the-fold section]
posted by taz (staff) at 5:26 AM on September 17, 2019 [1 favorite]

Not an expert, but perhaps a barn spider?
posted by forforf at 5:59 AM on September 17, 2019

Is it still out there? I've been playing with a phone app called Seek that's a joint project between National Geographic and the California Academy of Sciences. It's...nearly magic. Aim your camera at a plant, mammal, insect, lichen, whatever and it tells you in about 5 seconds the species name. It also works on pictures you've saved too. I believe the species lists are specific to your location and time of the year, which helps cut down on the search time.

I am not lying, I have been running around our yard like a madman identifying All The Things these past few days.
posted by jquinby at 6:21 AM on September 17, 2019 [5 favorites]

I agree it looks like a false black widow spider. I had put one I found in my garden on iNaturalist for identification, and even though I didn't get confirmation, when you click on the genus you can see more photos that have been positively identified, that look like your example. (Like Seek, the iNaturalist app also does AI-powered auto identification that's spookily good.)

I'm also a Friend To Spiders, but personally I wouldn't let one of these walk on me.
posted by snarfois at 7:42 AM on September 17, 2019 [1 favorite]

I'm also going with one of the false widows. I'm also in the Bay Area and I have a bunch of them in my house, I just let them hang out and they're great bug catchers. I did get bitten by one in bed recently (I woke up when it happened and found it on my pillow so it was almost certainly this spider, I'm assuming I must have rolled over on it when I was sleeping). I didn't have a terrible reaction to it, it was just tender and red and painful for a couple of days.
posted by primalux at 8:48 AM on September 17, 2019

Based on its size I think it could possibly be a Steatoda nobilis--I believe it's the largest of the false widows found in the U.S.--which has made an appearance in California and according to these folks is now widespread in the Bay Area.
posted by drlith at 9:46 AM on September 17, 2019 [1 favorite]

I'm also a Friend To Spiders, but personally I wouldn't let one of these walk on me.

I did decide I was going to put it down first before taking pictures, even though my arm would give better scale. I am a friend to all spiders, but it did have a bit of a widow-y vibe and I prefer to be a friend to black widows from a respectful distance.

Based on its size I think it could possibly be a Steatoda nobilis

I do wonder that myself, having just googled them. It was a strikingly large spider. However, the websites keep saying it's the same size as a black widow but it's surprisingly hard to find pictures of black widows that give good scale. I did find a picture of a nobilis with a 2 euro coin which is apparently about the size of a Sacagawea dollar, and I'd say this one was a little smaller than that, but not a lot. But then I was also having trouble finding good scale pictures of grossa.

Sadly, it has removed itself to another spot so I can't get any more pictures.
posted by tavella at 11:58 AM on September 17, 2019

Regarding size - I have seen Black Widows (L. mactans) on and off over the years, usually fairly small. Last summer I came across one in our garden (in/on some pallets I had turned into a compost bin) and it was...enormous. And unmistakable. The size caught me off-guard, to be honest. Looking at Wikipedia, perhaps she was egg-carrying to be so large.
posted by jquinby at 12:54 PM on September 17, 2019

So after consulting drlith's link, I think it is Steatoda nobilis. The page actually supplied body length numbers, and it was definitely far bigger than the 3/8th inch for grossa, and the 5/8ths ascribed to nobilis seems about right. Also thanks to BadgerDoctor for noting the light band as being particularly indicative.

I did check out the barn spider page, but it didn't have the hairiness of that species. Also, before it moved off the wire netting it spun a web, and it was formless, not an orb weaver web. I'll check this evening to see if it was just hiding in the debris underneath during the day and if it will come out again.

Thanks for all the help!
posted by tavella at 2:00 PM on September 17, 2019

Also thanks to jquinby for pointing out the Seek app, which I have downloaded.
posted by tavella at 2:06 PM on September 17, 2019 [1 favorite]

And a bonus for spider-lovers: the gorgeous web a very bold orb weaver spun across my entire front walk, determined to catch herself a whole human!
posted by tavella at 7:07 PM on September 17, 2019 [2 favorites]

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