Steatoda bites: Latrodectus lite

Many species of spider make their living around human habitations. Some of these guys can be very common where they are found. Occasionally, people do get bitten and do experience adverse effects. However, the incidence of these bites is far lower than most people realize. The vast majority of spider bites go unreported simply because they’re not noticed.

The genus Steatoda is one of these spiders. Around where I live, these guys are the most common denizens of the garage. I’ve yet to be in a house where I couldn’t find a few living either in the garage or somewhere else in the house (I currently have a rather large female residing behind my dresser). They’re pretty much everywhere and are very strongly associated with urban areas. They also have a pretty strong bite, something most folks don’t know about them.

Image Source: Tolweb

Usually, spider bites don’t require any sort of treatment. Many bites are either dry in which the spiders don’t inject venom or just not noticed, and this guy is no different. However, in a minority of cases the symptoms can be bad enough to need medical attention. Since Latrodectus and Steatoda are so closely related, the composition of their venom is somewhat similar. The bite of this species in the very few cases in which medical attention is required presents as localized pain and sweating at the bite site and radiates outward like the bite of a Latrodectus species. In the worst cases, patients have severe nausea, as well. All in all, in some cases the bite can be very similar to the bite of a black widow. And here’s why:

Fig. 1. SDS-PAGE gels and Western blots of S. grossa venom using RBSAV and polyvalent α-LTx antibody. In the gel (A) and both Western blots (B and C) molecular weight markings are shown on the left of the gel. The left hand lanes shows α-LTx followed by L. tredecimguttatus (Tre), L. hesperus (Hes), L. lugubris (Lug), S. grossa (Stea), and L. hasselti (Has) venoms. (A) SDS-PAGE gel showing protein components of Latrodectus spp., and S. grossa venoms. Note a consistent protein band in the toxin and venom lanes at approximately 130 kDa. (B) Western blot of α-LTx, Latrodectus spp., and S. grossa venoms using RBSAV. Note a protein band in the venoms consistent with that of α-LTx at approximately 130 kDa. Also note binding of antivenom to various lower molecular weight bands in the venom lanes. (C) Western blot of α-LTx, Latrodectus spp., and S. grossa venoms using polyvalent α-LTx antibody. Again note a band in all the venoms consistent with the presence of α-LTx. Also note the non-specific binding of the rabbit-derived antibody to lower molecular weight proteins in all the venoms (see text for more details).

The venoms of Latrodectus and Steatoda are very, very similar. I’m guessing many of the people who’ve read this may not have read an electrophoresis gel before, so let me explain what you’re looking at here. Electrophoresis is a simple method of looking at different cocktails of proteins and sorting them out. You take a mixture of something or other, stain it and run an electric current through a special gel and see how the proteins migrate. A western blot is a technique used to compare proteins. In this case, it’s being used to analyze the contents of the venom in these spiders. Electrophoresis organizes the proteins into groups of similar molecular weight because heavier proteins (measured by their molecular weight) don’t travel as far in the gel. They’re then transferred to nitrocellulose (which binds the amino acids the proteins are composed of) and then treated with antibodies (L. hasselti venom antibodies and alpha-latrotoxin antibodies in this case) to see how similar they are in a molecular sense. Anything which isn’t bound washes off, leaving these nice bands on the nitrocellulose (B and C).

A is the venom of the spiders ran in an electrophoresis gel. B is Latrodectus hasselti antivenin derived from horses and C is the antivenin for the active ingredient in Latrodectus bites derived from rabbits bound to the contents of the two types of venom. Protein bands for all these venom constitutents fall in about the same weight range which means that they are composed of similarly sized proteins. Since they react in a very similar manner to the antibodies of the various toxins, they are also similar in a molecular sense.

Since proteins in these venoms are really quite similar, the symptoms can be as well. The bites of these spiders can be very, very similar to those of black widows…in terms of both biochemistry and the symptoms experienced by some people who are bitten. Unfortunately, more work has been done on Latrodectus to isolate specific venom components, so the actual proteins are pretty poorly known in Steatoda. However, it’s thought that the venoms work in a very similar manner by increasing the amount of neurotransmitters sent across synapses.

So similar are these two venoms, that the antivenin for Latrodectus species are often used to treat the bites of Steatoda species.

Wondering how this species compare to something a bit more famous…perhaps yesterday’s sydney funnel web?

In a 39 month period, between Feburary 1999 and April 2002, there were 23 confirmed bites from species in this genus recorded in Australia. Seven required medical attention. That’s about 7 bites per year, maybe two per year needing medical attention.

If you want to compare this to something a bit more mundane, Salmonella outbreaks between 1993 and 1997 sickened more than 85,000 here in the US. Compare that to 10-15 bites per year requiring any sort of medical attention for Atrax and a grand total of 2 bites bites per year requiring medical attention for the species mentioned in this post…well, it’s just not very much. Especially when you consider the intimate association of this species with humans and the fact that Steatoda has a much wider distribution in Australia than do Atrax and similar species.

The problem with a lot of spider bites is that many times, they are a diagnosis of exclusion. Many times, the spider isn’t caught or identified and whatever ailment is seen may just be assumed to be the bite of a spider. This is especially the case in instances of idiopathic necrosis. The cases of suspected spider bites far outweigh the instances of confirmed spider bites and often as I’ve pointed out before, sometimes this can cause some quite serious misdiagnosis.

I’m attempting to give some perspective to spider bite incidence and show people that spiders really aren’t all that dangerous. In the popular media, spiders and other insects are often elevated to the status of bears, sharks and lions (who also get screwed over as a result of popular perception) when in reality, there are more mundane things which kill people in areas where medically significant spiders are found.

Now…when dealing with spiders, you should always keep a level head. They should be treated with respect because of what they are. However if you should find one in your grapes, in your bedroom or anywhere else…you should realize that you are in no danger at all. A simple film canister, CD case, or whatever else you just so happen to have handy will suffice to transport the spider safely outside.

I am planning on doing a series of posts about Cheiracanthium, Latrodectus, Loxoceles and Lamponidae this week and next. Someone pointed out that this post communicated something I didn’t intend due to the fact I didn’t pay close attention to how I worded some of the stuff in my original posts (and last week’s Atrax post), so I’ve went back and edited it where I needed to and gave a more concise explanation of electrophoresis and western blotting.

Ibister G. K., White J. 2004: Clinical consequences of spider bites: recent advances in our understanding. Toxicon 43 (2004) 477–492

Geoffrey Isbister, Michael Gray (2003). Effects of Envenoming by Comb-Footed Spiders of the Genera Steatoda and Achaearanea (Family Theridiidae: Araneae) in Australia Clinical Toxicology, 41 (6), 809-819 DOI: 10.1081/CLT-120025346

A Graudins (2002). Clinical and in vitro evidence for the efficacy of Australian red-back spider (Latrodectus hasselti) antivenom in the treatment of envenomation by a Cupboard spider (Steatoda grossa) Toxicon, 40 (6), 767-775 DOI: 10.1016/S0041-0101(01)00280-X