Center for Invasive Species Research

How to identify (and misidentify) Brown Widow

The brown widow spider, Latrodectus geometricus, is not native to the United States. For decades, it lived only in peninsular Florida in the U.S. but in the first decade of the twenty-first hundred, it spread unusually quickly, is immediately found from Texas to South Carolina and is well established in the urban areas of Los Angeles, San Diego and surrounding suburbs. In the westerly United States, accurate identification of this spider can be unmanageable. The brown widow is a tangent spider with a series of ashen stripes. unfortunately, immatures of the native black widow spider, Latrodectus evening star, besides are tangent with white stripes and are frequently mistaken for brown widows. There is TREMENDOUS variation for both of these species as they grow from babies to adults. In order to master identifying them, many specimens need to be examined. Below is a graphic comparison of the two species with ways to differentiate between them. many people send in ball weavers orb weavers of the genus Neoscona and Araneus. Orb weavers have spines on thier legs, widow spiders have no spines. Please check the internet to identify orb weavers to reduce the chance of misidentification .
Egg sac
This is the easiest way to tell a embrown widow from a black widow. The egg sauk of the brown widow is round and yellow with many little silk spikes sticking out from its surface, looking like a big pollen ingrain or one of those harbor mines from World War II. The egg theca of the western bootleg widow is either round or pointed at the crown, jaundiced and smooth .

eggsac (c) CISR latro hes eggsac (c) CISR
Brown widow egg sacs Black widow egg sacs

Newly emerged spiderlings
Once the babies emerge from the testis pouch, things get a little confuse. Although the brown widow may look a short bite like the pornographic that it is going to grow up to be, the western blacken widow looks NOTHING like a black widow female. Baby western black widows have tan legs, tan cephalothorax with a black longitudinal band and a white abdomen with black spots. Although these two baby spiders look reasonably alike, the brown widow babies have more brown on them .

latro geo baby (c) CISR latro hes baby (c) CISR
Brown widow baby spiderling (live) Black widow baby spiderling (live)
latro geo babies dead (c) CISR black widow babies in alcohol (c) CISR
Brown widow baby spiderling (dead) Black widow baby spiderling (dead)

Where the problem comes in
The trouble with properly identifying mature brown widows from unfledged western total darkness widows comes when the spiders are about half mature. The brown widows change a little but western black widows change a batch. The key to by rights identifying the two species lies in those black dots that you can see on the spiders ’ abdomen. Of secondary utility, the cardinal longitudinal stripe on the clear part of the abdomen can likewise help oneself differentiate species. As both species of spiders grow bigger from babies, the abdomen background turns black colors and stripes appear on the abdomen.

letgeom abdominal spots (c) CISR latro help immature abdomen (c) CISR
Brown widow female abdomen Western black widow immature abdomen

At first these spiders may look very like. however, pay attention to the lateral diagonal stripes on the abdomen. In the brown widow, it looks something like a feel of a hand projecting up and the finger is holding a boastfully black rectangular blotch. Compare that to the immature westerly black widow and you see that the idle colored stripe is more of a straight line or may be flattened a little at the top. however, the blacken scatter at the peak of the lightly colored person line is little and blobby .
The next thing to look at is the longitudinal chevron. In the embrown widow, it only extends about half way up the abdomen from the rear. In the western black widow, the stripe extends about all the way up the abdomen. besides notice that the forwardmost point in the brown widow is isolated from the respite of the stripe and is about twice adenine wide as long. The lapp position that would have the dot on the immature western black widow is continuous with the chevron ( at least in the early stages of animation ) .
As western black widows mature, they develop more dark paint in the background area, the stripes start to break up into nebulous isolated patches and finally disappear as the spider continues to molt and adds dark pigment on its way to turning wholly black. sometimes there is a bright orange or red stripe in the middle of the longitudinal abdominal stripe. This will besides fade and get flimsy as the spider matures .
The brown widow can have some orange in that longitudinal stripe but it will never be bright bolshevik. Below will be a series of pictures of brown widows then black widows to show you the capital magnetic declination in each species as they mature. Realize that distinguishing the two species takes lots of practice and examining lots of specimens. Brown widows can vary from about a white to being about a black as a black widow .

latro geo abdomen (c) CISR abdomen (c) CISR
latro dark abdomen with spots (c) CISR brown widow orange abdomen (c) CISR

Brown widow abdomens  showing light colors ( upper berth leave ), orange in longitudinal chevron and identical pale blotches at the top of the diagonal stripes ( amphetamine properly ), a dark abdomen with identical blue blotches on top of the diagonal stripes ( lower left ) and a strange one with orange shade all over ( lower right ).

latro help immature abdomen (c) CISR latro hes immature abdomen (c) CISR latro hesperus red dots (c) CISR

Immature western black widow abdomens showing typical tan backdrop with orange-red longitudinal stripe ( left ), showing a bit black background coloration but the small black dots on lead of the blank diagonal stripes are scantily visible, notice how the central longitudinal chevron undulates slightly and the orange stripe pinches off at places ( center ), and another darkening specimen where the central red longitudinal band is now breaking up into individual spots. These spots will dissipate as the spider grows and darkens to black ( correct ) .

lat geom anterior abdomen (c) CISR Lat help anterior abdomen
On the front facing portion of the brown widow abdomen (left), the light colored lines do not converge in the middle whereas in the immature black widow (right), the line is continuous.  In addition, the forwardmost spot in the middle of the brown widow abdomen is as wide as long or often wider than long.  In the immature black widow, the forwardmost spot is longer than wide and looks like an arrowhead.  In the black widow, these markings become nebulous as the spider loses its light coloration and becomes solid black.  Sometimes the adult female black widow retains a portion of the continuous line in the front part of the abdomen.
 
lat geom hourglass (c) CISR lat hesp hourglass (c) CISR
The hourglass of the brown widow (left) is wider on the bottom than the top and the bottom half of the hourglass is larger than the top half and is “puffy” with a fuzzy, indistinct outline.  In the immature black widow, (right) the top half of the hourglass is wider than the bottom and the top half of the hourglass is larger than the bottom half with the outline being more distinct and crisper. 

Adult females
Many sources will tell you that a brown widow is tan and has an orange hourglass. What actually is the lawsuit is that most are like that but there is enormous mutant as you can see with the pictures above. Although the typical case is tan with an orange hourglass, some brown university widows are very dark and have a hourglass that isn ’ deoxythymidine monophosphate precisely bright red but is red-orange enough that you wouldn ’ t say it looked good orange ; these can be mistaken for black widows. On the close up, you can see that it looks like a loss hourglass with an orange molding .

brown widow tan with orange hourglass (c) CISR brown widow hourglass closeup (c) CISR
Typical tan brown widow Brown widow hourglass
brown widow with red hourglass (c) CISR lat geom black abdomen (c) CISR
Dark brown widow with red hourglass Above: brown widow that is almost as dark as a black widow.  Notice that the abdomen isn’t as shiny and reflective as that of a black widow and there are traces of brown coloration.  It was initially identified by its bottom-heavy hourglass and verified when it produced a spiky egg sac typical for the species.
lat geom black morph reverse (c) CISR
Above: brown widow that is almost as dark as a black widow.  Notice that the abdomen isn’t as shiny and reflective as that of a black widow and there are traces of brown coloration.  It was initially identified by its bottom-heavy hourglass and verified when it produced a spiky egg sac typical for the species.

Western black widow females
Of course, the familiar radiation pattern of the black widow is very outstanding and looks nothing like the baby that emerged from the egg pouch .

latro female habitus op (c) CISR
Males
Males of both species are smaller than the females but the brown widow males are much smaller than bootleg widow males. Both species retain much of the color of the juveniles. On identical rare occasion, western male black widows can be black with white stripes .

latro geo male habitus op (c) CISR

black widow male (c) CISR latro hesp male (c) CISR black widow male closeup (c) CISR
Male western black widows Male western black widows Close up of male western black widow spider showing juvenile abdominal coloration

Size comparisons
Below are pictures of male and female brown and western black widows taken with the like scale so their sizes can be compared .

latro geo sizes (c) CISR black widow sizes (c) CISR
Male and female brown widow Male and female western black widow

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