Currently viewing the category: "Cobweb Spiders"

Subject:  Not a black widow, or is it?
Geographic location of the bug:  Apartment in eastern Massachusetts
Date: 10/17/2017
Time: 07:04 PM EDT
I found this odd looking spider in my apartment. My first thought was black widow, given its shape and the pattern on its back, but the coloration is different. What is this spider?
How you want your letter signed:  Joe

Cobweb Spider

Dear Joe,
Though your image is quite blurry, we concur that this does look like a Widow in the genus
Latrodectus, and we believe it might be a highly variable Brown Widow, a species recently introduced from Africa.  According to BugGuide data, it has been reported from nearby Maryland, and in Southern California in recent years it has nearly supplanted the native Black Widow.   While we entertain that possibility, we think this is more likely a harmless member of the Cobweb Spider family, like possibly Steatoda triangulosa which is pictured on BugGuide.

Update:  October 22, 2017
Thank you. We’ve gotten a picture of one of these spiders’ underside and observed their behavior a bit. They’re aggressive if their webs are disturbed, and roll into a ball if they fall. The webs themselves are messy and thee-dimensional, but not really funnel shaped.
Does this affect the identification?

Cobweb Spider

Hi Joe,
We agree with Cesar Crash who provided a comment that this is NOT a Brown Widow, and most likely a harmless Cobweb Spider.  Your new image confirms that conclusion.

Subject:  Tiny spider found near farm
Geographic location of the bug:  Blacksburg, VA
Date: 10/10/2017
Time: 11:01 AM EDT
I found this spider near a farm. Caught it in a jar and it laid its eggs, and now looks a lot more deflated. What species could she be? Thanks.
How you want your letter signed:  Daniel

Dewdrop Spider

Dear Daniel,
This is a kleptoparasitic Dewdrop Spider, probably
Argyrodes pluto, which according to BugGuide has a range of “USA – From Maryland, Virginia, Missouri, southwest to Chihuahua and Jamaica.”  Kleptoparasites steal food from other species.  According to BugGuide:  “Argyrodes spiders (and related genera) are kleptoparasitic. They live in the outer edges of other spiders’ webs and move in to steal prey when the coast is clear. Apparently the method of at least one species (Argyrodes nephilae) is to attach a line of silk then cut the wrapped prey out of the host web. The bundle swings free and can be taken to the outskirts of the main web to be eaten in relative safety.”

Subject:  Black Widow Spiders
Geographic location of the bug:  Northern New Mexico
Date: 10/04/2017
Time: 12:05 AM EDT
Good evening.
I moved to Santa Fe from Southern Oregon four months ago for work and I have never encountered female black widow spiders like this. We have killed eight large, female specimens in the house over the past two days.  Most of them were on the move in broad daylight, and surprisingly aggressive.  Two of them were actively sharing a web.  I captured one in my bathroom, and confirmed the red hour glass. I’ve never known female widows to act like this, unless defending egg sacks. Is this a sub species native to New Mexico, or some sort of infestation I was previously unaware of?
How you want your letter signed:  Alexa Rense

Black Widow

Dear Alexa,
According to BugGuide:  “The
Latrodectus genus breaks down taxonomically into approximately 31 recognized species, five (5) of which are found in the United States; four (4) species are native, one (1) species (L. geometricus) was introduced.”  According to BugGuide data, it is the Western Black Widow that is found in both Oregon and New Mexico.  While the bite of a Western Black Widow can be dangerous, they are not an aggressive species, though many female spiders will defend eggs and young.  We are lamenting the loss of native Western Black Widows in Los Angeles where they seem to have been entirely replaced in recent years by the invasive Brown Widow.

Subject: Is this a Black Widow Spider
Location: Johnstown, PA
August 21, 2017 2:53 pm
My name is John and I am the safety director for a company based out of Johnstown, PA. Earlier today, August 21, 2017 I was approached by two mechanics working on a truck with a concern over a spider. Today was the day of the eclipse and was a very nice warm day, temperature mid to upper 80’s. the spider was located in a sealed portion of the truck that under normal circumstances is very dark. there was a repair needed in the area so a hatch was opened up to reveal the webbing and the spider. After multiple people viewed the spider there was an ensuing debate on whether it was a Black Widow or not. Please help.
Signature: John Gregorchik

Black Widow

Dear John,
Because of the red hourglass marking on the ventral surface, we are 100% confident this is a female Black Widow Spider.

Subject: Strange Spider?
Location: Upstate New York
July 11, 2017 9:14 pm
Dear Bugman,
My son and I located what we believe to be some sort of spider weaving a web under our porch light. We were quite curious as to what type of spider it might be. I am thinking some type of Orb Weaver? Any help would be greatly appreciated. So sorry for the quality of the photos, the bug was quite small. Thank you.
Signature: Heather

Cobweb Spider

Dear Heather,
We believe we have correctly identified your spider as a Cobweb Spider in the family Theridiidae, and it is a species without a common name,
Rhomphaea fictilium, thanks to this BugGuide image.  According to BugGuide, it is:  “widely scattered in the U.S., but reportedly rare; also throughout most of Canada.”  We located this interesting information on Spiderbytes:  “As well as having wonderfully strange morphology, Rhomphaea have rather unusual habits. Most spiders are generalist predators, and spiders in the family Theridiidae typically build tangle webs that they use to catch crawling insects and other arthropods, including other spiders. Rhomphaea, unlike most of their relatives, specialize on hunting other spiders. They do sometimes build their own rudimentary webs from just a few silk lines, but they also enter the webs of other spiders and use aggressive mimicry to hunt their owners. Rhomphaea will pluck the web and produce vibrations that lure the resident spider out to investigate what they perceive to be prey caught in the web. The web-building hunter then becomes the hunted, tricked into the approaching the dangerous intruder. Rhomphaea fictilium have been reported to prey on other theridiids, orb-weavers (araneids), sheet-weavers (linyphiids) and others.”

Cobweb Spider

Wonderful!  Thank you so very much for your help.  It was fascinating to read about this spider.
Thank you,

Subject: Is this a Dangerous Spider – Sure looks like it to me
Location: West Los Angeles
July 10, 2017 5:39 pm
Hi Bugman,
As much as I love butterflies, I don’t get along with spiders. Can you please let me know if this one is dangerous?
These are the best pics Icould take, but if you enlarge them the spider is quite visible.
Signature: Jeff Bremer

Brown Widow and Egg Sac

Dear Jeff,
Both the Brown Widow Spider and her egg sac which are pictured in your image are quite recognizable.  According to BugGuide:  “The brown widow is highly variable in color. It may be almost white to almost black. Typically, it is a light to medium brown, with an orange-to-yellow hourglass marking on the underside of the abdomen; the coloration of the hourglass often is a good indication of this species. The leg segments are banded, with one half of each segment lighter in color than the other half. The back often has a row of white spots (rarely orange or light blue), and there are a few white stripes on each side. Darker individuals lack these markings and are difficult to distinguish from black widows. If an eggsac is present, this is the best identifying characteristic. Brown widow eggsacs are tan, spherical, and have many small tufts of silk sticking out from them. They resemble a ‘sandspur.’ The other widows make white, smooth eggsacs that tend to be pear-shaped. ” BugGuide also provides this information:  ” Widow Bites:  NOTE: It is recognized that this particular species of widow is most likely not medically significant (not an immediate medical concern to those who are bitten). The brown widow produces clinical effects similar to that of the black widow but the typical symptoms and signs being milder and tending to be restricted to the bite site and surrounding tissues. (Print Ref 1)  Brown widow spiders usually curl up into a ball, and drop to the ground as a primary defense. It is highly recommended that people leave this spider alone; observe, but don’t touch.  The brown widow is an extremely timid spider which has rarely been reported to bite.”  The Brown Widow is a non-native, introduced species that has gotten quite common in Southern California as well as the entire southern portion of the U.S.

Thanks Daniel,
It’s hard to know when to be worried and when not.