This year appears to have produced a bumper population of Black Widow (Latrodectus) spiders. Having had too many close calls with these arachnids, I decided to eliminate as many as possible before I became a victim. I have no problems with other spiders and welcome them in the garden, appreciating their effect on the insect population and delighting in the beauty of a perfectly formed Orb spider's web. However, this summer it seemed that almost everything I touched had a Black Widow lurking underneath; when I filled my watering can one came out of the top as the water level rose, when I harvested my squash there was a large one under one of the fruits, the children's tree house had them in the corners, and as I was fitting a child's car seat into my car one emerged from under the seat as I tightened the final strap.  Enough! I had to take action. 

The first thing was to find out as much as possible about the habits and life cycles of the Black Widow, and the IPM website http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74149.html was invaluable for this.  It shows photographs of not only adult female Widows with their shiny, black round bodies with the red hourglass markings on their lower abdomen, but also the male and immature forms, both of which look very different.  Fortunately, these spiders are shy and tend to retreat to a hole or crevice if disturbed. This very habit means that the unwary may accidently disturb them and induce a bite – often by putting shoes on that have been left outside or by picking up such things as logs or pots that have one underneath. Their bite contains a neurotoxin which induces symptoms such as a localized rash, severe muscle cramps, possible paralysis of the diaphragm, nausea, vomiting, and changes in vision. Anyone bitten should use an ice-pack on the bitten area and then seek immediate medical help, if possible taking the culprit with them to confirm identification.

Black Widow spiders like to live in undisturbed clutter around homes and seem equally at home underneath garbage cans,  under the covers of irrigation set-ups, in wood piles, in natural stone facing of retaining walls and houses, or in seldom-used children's' plastic toys where they build webs in the wheels and under seats.  They are common in the darker corners of garages and sheds and will occasionally be found in similar spots inside homes.  Their webs are not what we think of as the classic spider's web but rather a disorganized collection of very strong threads, often with bits of leaves or dead grass hanging in them and frequently containing small and very tough egg sacs which may contain up to three hundred eggs.  The female can produce up to 10 of these from one mating!  On average, they live for about three years. The population of these spiders is only maintained if there is enough food for them. It is not likely that there will be a shortage, since they will eat any insect: beetles, crickets, cockroaches and even scorpions.

I wanted to gain some control without the use of chemical sprays. I identified various webs, but as soon as I approached, the spiders would take cover in some inaccessible spot.  Then a neighbor suggested that I go out after dark with a flashlight so, armed with an old shoe, I chose a warm moonlit night to begin my “Widow Vendetta”.  I could not believe just how many spiders there were!  On a raised planter bed with concrete stone edges, there was a large adult female about every 18 inches around the whole circumference. They were sitting in their webs upside down with their red hourglass markings clearly visible and they did not scuttle away when I shone the light on them, making a quick dispatch an easy matter.  I then concentrated around the house foundations where there were dozens of tiny spiderlings setting up home.  The flashlight had the benefit of casting their shadow onto the concrete path which made their exact position easier to see, and I often killed 30 spiders in one night.  (I am relieved that this eccentric behavior has so far not appeared in the local “Police Blotter”)!  I followed this routine every couple of weeks throughout the summer and swept the walls with a flat broom afterwards, which made it easier to spot new webs as they appeared.  I have pruned vegetation back from beside the house and have tried to limit storage of items near entrances. A pressure jet of water could be used to dislodge some from more difficult positions, although that would surely be an egregious use of such a precious commodity during a drought.

Praying Mantises are particularly fond of these spiders, and some wasps parasitize them, so I am hoping that due to our combined efforts, we will gain some control. Meanwhile, I have been wearing gloves when performing gardening tasks, and have been carefully checking and brushing logs and plant pots before bringing them into the house. Only time will tell whether my efforts will make a noticeable difference to the Black Widow population, or whether I have upset the natural balance enabling some other noxious species to take hold instead.

For more info on Black Widows, see: http://www.livescience.com/39919-black-widow-spiders.html