Thursday, May 25, 2006

Friday Spider blogging

Previous Spider Fridays:

5/19: The Sydney Funnel-Web
5/12: The Black Widow

Hello everyone, and welcome to the third weekly edition of Spider Friday--because I spend so much time in front of my computer that the only friends I have, have four times the number of legs I do! And I want you to meet them.

I know I promised you a particular spider in my last diary, but I had requests from several people who have a personal, vested interest to do one about the Brown Recluse before I moved on--so here it is. It isn't my intention to scare the living wits out of everybody by focusing exclusively on things that could kill you--that's George Bush's job--so after this week, I will focus on spiders that are not considered a serious threat. But at the end of this diary, as a special bonus treat, I will show you: THE SPIDER WITH THE MOST LETHAL VENOM IN THE WORLD.

So move below the fold and enjoy yet another round of Spider Friday!



Kingdom: Animalia (Animals)
Phylum: Arthropoda (Arthropods)
Class: Arachnida (Arachnids)
Order: Araneae (Spiders)
Infraorder: Araneomorphae (True Spiders)
Family: Sicariidae (formerly Loxoscelidae)
Genus: Loxosceles (Recluse Spiders)
Species: reclusa (Brown Recluse)

BACKGROUND:

The Brown Recluse is simultaneously the most overreported and the most underreported spider in the United States--over-reported because every single arachnophobe around who encounters a small brown spider, no matter what part of the country, automatically thinks it's a recluse and panics; and the most under-reported because Brown Recluse bites are often misdiagnosed. So with that in mind, let's start with identifying a Brown Recluse spider, and correct some misconceptions.

First and foremost, this map--courtesy of the Burke Museum, University of Washington--displays the traditional range of L. reclusa:



If you don't live in the area depicted in green, chances are that whatever you think might be a Brown Recluse, probably isn't. One might think that the Brown Recluse would have been able to hitch rides and spread across to other areas, but it's scientifically demonstrated that Brown Recluses almost never appear outside their traditional endemic ranges.

Brown Recluses, when full-grown, have a legspan about the size of a quarter--so they're not very big. Furthermore, Brown Recluses are also sometimes called Violin (or Fiddle) Spiders, because they have a marking on their carapace that looks like an inverted violin:


(Photo credit: U. of Nebraska-Lincoln Dept. of Entomology; taken by Jim Kalisch.)

The "violin", however, shouldn't be considered as the most telltale characteristic. Some specimens have violins that are irregularly shaped, if not indistinguishable--and juveniles don't have violins at all. A far more telling characteristic, should you be willing to look so closely, is the arrangement of the eyes. Brown recluses, and their close relatives in the Sicariidae family, are unusual in that they have six eyes, divided into two sets of three:



This picture perfectly demonstrates not only demonstrates the traditional fiddle, but also the eye arrangement--which is visible with the naked eye, though a magnifying glass helps:



Only 430 species of spiders--less than one percent of spider species worldwide--have six eyes. The other 99% of spiders have eight eyes in various arrangements--like this cute little jumping spider whose picture I needed to have an excuse to insert into this entry (with four more eyes in the back--the pattern is symmetrical):



Brown Recluses also have solid coloration, and a relatively smooth appearance. If you see a spider that looks hairy, or is mottled, or has any other such variation, it's almost certainly not a recluse. The abdomens of recluses can vary in color, but are always uniform. Here's a lighter abdomen:



And a darker one:



Here's a fantastic photo featuring all the defining recluse characteristics:



So there are some tips for identifying Brown Recluses--we'll talk about their relatives a bit more later.

Brown recluses build webs, but they don't use them for hunting--they're exclusively for lining retreats:



Brown recluses hunt at night, but unlike most spiders, brown recluses do not restrict themselves to hunting live prey--they are very shy and non-confrontational, and will scavenge as well as hunt. In experiments, recluses have actively preferred to eat insect that have been dead for two weeks as opposed to hunting live prey. Here is a gratuitous picture of a brown recluse eating a cricket (this picture also shows the distinctive eye arrangement):



When brown recluses hunt, they hunt by stealth, waiting for prey to pass close by before pouncing for the kill. Recluses will hunt exclusively at night, preferring to hide during the day, as their name implies.

LIFECYCLE:

Recluses reproduce mostly during spring, although this can extend all the way through July. There is little sexual dimorphism between female and male spiders, though a trained eye can recognize it. The male shown below has a slightly different abdoment shape, as well as the palps specialized for sperm delivery:



Males recognize females through pheromones and begin a courtship dance to prevent the female from thinking that he's lunch. If his efforts are successful, mating ensues shortly afterward. The female will then produce at least one egg sac containing anywhere between 30-50 eggs:



Spiderlings hatch in a few weeks, where they are fed by mom for a while and then go wandering on their own.

BITES:

Brown Recluses are, as explained above, extremely shy and, well, reclusive. They generally try to avoid situations as much as they can, and they only bite when they get trapped. Since recluses like to hide during the day in cozy spots like bedding, furniture and clothes, bites occur most often by accidental contact--like rolling over in bed, or putting on a shirt. Brown Recluses also love sheds and garages, so bites occur frequently from hanging out in those areas.

Brown recluse venom contains a powerfuly haemolytic cytotoxic enzyme called Sphingomyelinase D--that is to say, it creates blood vessel leakage and dissolves surrounding tissue. A brown recluse bite will not be felt at the time of the bite, but will be shortly followed by pain, swelling and redness at the site of the bite. After a time, the area of the bite will necrotize, and the tissue will harden and turn black:



This dead, hardened tissue will then slough off, leaving a open, necrotic lesion, which can take months to heal.

Brown recluse bites are a serious matter, but contrary to popular belief, most bites don't require hospital treatment--usually, the victim is able to heal with little or no noticeable scarring in a short time, provided that proper care is taken to prevent infection. There are severe cases, however, where hospitalization is required, though this can be just as often the result of a secondary infection as the result of the bite itself--and often, it's hard to tell which.



Sometimes, recluses can cause necrosis the size of dinner plates:



Usually, bite effects are localized and not systemic, but in a few cases, bites can cause nausea, chills, vomiting and renal failure. In a very small percentage of cases, brown recluse bites can be a recurring injury. We don't exactly know why this is, but in some cases, venom may actually get trapped inside tissue--and when it is activated, it is like being bitten all over again. This recurring necrosis has been known in some cases to recur for years, with no confirmation as to the actual trigger.

But cases like this aren't actually all that common. As always, if you think you've been bitten, it's best to try to collect the spider that got you--even a squashed specimen can be identified by a trained expert.

RELATIVES:

The brown recluse has several relatives that should be considered equally armed and dangerous. Let's take some other members of the Loxosceles family first. Here's L. rufescens, the Mediterranean Recluse:



The distinguishing characteristics of rufescens is first and foremost its reddish coloration--"rufescens" means "blushing" in Latin--but the eyes also have a different configuration: in rufescens, as you can tell from the picture, the two rear eye pairs are separated from the front pair by a difference of 1 1/2 to 2 diameters, whereas in reclusa, the difference is usually 1 diameter or less.

There is also L. deserta, the Desert Recluse. It resides in the deserts of Southeastern California, and has a lighter appearance, a less pronounced violin, and less toxic venom:



The Chilean Recluse, L. laeta, was introduced to eastern Los Angeles in the 1960s and has since turned into an established but small population. Its venom is more toxic than L. reclusa but the effects are more systematic and typically result in less tissue necrosis:



AND NOW FOR THE MOST LETHAL SPIDER ON EARTH:

The most lethal spider on Earth has, in fact, never been proved to have ever bitten anyone. It is a cousin of the recluse spiders, and is classified in the Sicarius (literally, "assassin") genus. It is S. hahnii, the SIX-EYED SAND SPIDER (or six-eyed crab spider):



These assassins are very well-camouflaged, and hunt by ambush:



This spider lives in the deserts of South Africa, and likes to bury itself in the sand waiting for prey to come by--can you find the spider?



Fortunately, this spider, like the recluse, is very shy. But toxicology studies have shown that this spider's venom--also a haemolytic cytotoxin--is the most venomous of any spider, and that any bite is likely to produce a fatality.

That wraps it up for Spider Friday. I hope you've enjoyed it. Stay tuned next week for the Bola Spider! (I mean it this time).