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 The
brown widow spider became established in Southern California in early 2000
and has mixed with the local spider fauna in urban Los Angeles and San
Diego. This spider is continuing its
expansion in California and could possibly move northward into all parts of
the state.
It may
have evolved in Africa but it was first described from South America, which
adds confusion as to where it might have originated. It is a cosmopolitan tropical and
subtropical spider having established populations in Hawaii, Florida, some
Caribbean Islands, parts of Australia, South Africa, Japan, and Cyprus. In North America, the spider was
restricted for many decades to Florida.
However, after the year 2000, it began showing up in other Gulf Coast
states. Brown widows are now known
from Texas to Georgia and South Carolina.
As specimens were found in new locations in the southeastern United
States, this species was simultaneously being collected with greater
frequency in southern California. The
first specimens were collected in Torrance in 2003. After that, the spider was found with greater frequency in
other southern counties.
Unlike
its starkly black-and-red colored relative, the black widow, the coloration
of a brown widow consists of a mottling of tan and brown with black accent
marking. In mature females, there is
usually a dorsal longitudinal abdominal stripe and three diagonal stripes on
each flank. At the top of each diagonal
stripe, there is a black mark, which is rather conspicuous and
square-ish. The Brown Widow Spider
does have an hourglass but it is typically an orange shade rather than the
vivid red of a black widow. The brown widow appears similar to immatures of
the western black widow spider, the latter of which has smaller black spots
on the top of the diagonal abdominal stripes and more olive grey background
coloration. Being able to
distinguish brown widows from
immature black widows is, therefore, difficult and requires some
practice. However, a more diagnostic
feature of a brown widow is its egg sac.
Most spider egg sacs that are free (i.e., are not attached to flat
surfaces) look like a lemon drop candy or a little cotton ball with
indistinct edges. The egg sac of a
brown widow has multiple silk spicules projecting out from the surface. The egg sac has been described as looking
like a large pollen grain or a World War II harbor mine designed to blow up
ships. The egg sac of the Brown Widow
Spider is so distinctive that it is readily recognizable. Brown widows may occupy the same niche as
black widows, therefore, there may be a change in the species
composition. Considering that the
brown widow is less dangerous and may be supplanting the native western black
widow from habitats, it is conceivable that the risk of serious injury from
overall spider bite may decrease in southern California as the brown widow
spreads.
Brown
widows are prolific breeders in that they can produce many egg sacs in a
lifetime, often several in fast progression. They lay about 120-150 eggs per
sac and can make 20 egg sacs over a lifetime. Comparatively, the larger western black widow spiders lay about
300 eggs per sac but make 10 or so egg sacs before they die. They build webs in secluded, protected
sites around homes and in woody vegetation with branches. Some typical sites selected by brown
widows for web building are empty containers such as buckets and nursery
pots, mail boxes, entry way corners, under eaves, storage closets and
garages, recessed hand grips of plastic garbage cans, undercarriages of motor
vehicles that are stationary for long periods, and the undersides of outdoor
furniture and wrought iron railings.
They choose places that are more exposed than sites chosen by black
widows and hence, appear to be at higher risk for interactions with humans as
for as bites are concerned.
The
bite is minor in comparison to that of other species. Although some suggest that quantity wise
brown widow spider venom is as toxic as other widow species. Dr. Mark Hoddle reported that nn African study
with 15 verified bites demonstrated that the brown widow spider bite victims
showed none of the classic symptoms of latrodectism, a response induced by
neurotoxins in the venom of spiders in the genus Latrodectus (e.g., brown widows, black widows [L. mactans], Australian redbacks [L. hasselti], European black widow [L. tredecimguttatus], and New Zealand's
katipo spider [L. katipo]). The reason for the weaker effect of brown
widow bites on humans may relate to the fact that brown widow does not have or
cannot inject as much venom as its larger relatives. The two major symptoms of a brown widow
bite were that the bite hurt when it was inflicted and it left a red
mark. These two symptoms are not much
different from the bite of normal household spiders. However, there is one recent report of
a person with a brown widow bite
showing severe symptoms required hospitalization.
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