So I’m a Spider, So What?- Spider size vs venom toxicity

Spider Size vs Venom Toxicity

I am firmly convinced that Okina Baba is a big fan of spiders, or at least has more than a passing knowledge about them. This is due to the number of spider references in “So I’m a spider, So what?”. Many of Kumoko’s spider attacks are based on the abilities of a variety of real-world spiders, some of which aren’t the most common, spiders either. Now in the world Kumoko finds herself, one can level up or change into different versions of themselves. In Kumoko’s case it’s other types of spiders found in the world she is currently living in.

spider venom

This brings up another aspect of spiders, which is the common notion that the larger the spider, the less dangerous its venom. FYI- I will be looking at how dangerous it is to people.

Venom vs. Poison

A venom is a toxin that is injected into the target. This usually happens via fangs or a stinger of some sort.

spider fangs

A poison is a toxin that is ingested by eating an organism that contains a toxin. An example would be a puffer fish, which can be dangerous when eaten.

puffer fish

Do all spiders have venom?

The short answer is yes, virtually all of the 35,000 species of spiders have some sort of venom. That being said, not all of them are dangerous to humans.

What happens during a spider bite?

The first step is fairly obvious, the spider has to actually bite you. The next step is that the venom needs to be injected into the body, or envenomation. Two things have to happen for this to occur: first, the fangs need to be able to penetrate your skin. While this is not an issue for most spiders, it is a problem for other venomous organisms.

spider fangs

The next step is that the spider must inject the venom into the organism that is has just bitten. This is a given in spiders, but there are sme organisms that do not inject venom with every bite, namely some snakes. When it comes to the venom itself, there are two things that matter, the amount and the type of venom that is injected into the bite. Fun fact: contrary to popular belief tarantulas do not have large venom glands or inject a lot of venom into the organisms they bite. I can also say from personal experience that tarantula bites are not dangerous, but they do hurt because their fangs are quite large.

Types of Venom

Unlike spider silk, each spider or group of spiders will use different toxins in their venom, and each spider only makes one kind of venom. In broad strokes, there are 2 types of toxins found in spider venom.

Cytotoxin/Necrotoxins– These toxins cause the death of cells in the area around the bite. This type of toxin is used by brown recluse spiders.

Neurotoxins– These toxins directly influence the nervous system and tend to be faster acting than other types of toxins. They are used by black widow spiders.

Don’t forget that you also have to consider the amount of spider venom that is injected with each bite, which varies with spider size.

Spider size vs. Venom toxicity

Does the size of the spider have anything to do with how toxic the spider is? The short answer is yes, there is a general trend in spider size vs. how toxic the spider venom is. I took the body length of the 9 most venomous spiders according to Encyclopedia Britannica, and compared it to the body length of the 10 largest spiders according to the Conservation Institute.

Average body size of the most poisonous spiders according to encyclopedia Britannica

Brown recluse spider 13mm

Brazilian wandering spider 32.5mm

Yellow sac spider 7.5mm

Wolf spiders 22.5mm

Black widow spiders 6.5mm

Brown widow spiders 12.7mm

Red widow spider 12.7mm

Red back spider 6.5mm

Funnel web spider 30mm

Average of all the spiders on the list- 15.9mm

Body size of the largest spiders in the world according to the conservation institute

Huntsman spider 22.5mm

Brazilian wandering spider 32.5mm

Camel spider 60mm

Hercules baboon spider- 100mm

Colombian Giant Black Tarantula- 90mm

Brazilian giant tawny red tarantula- 100+mm

Poecilotheria rajaei- 102mm

Brazilian Salmon Pink Birdeater- 100+mm

Huntsman spider- 25mm

Goliath Bird-Eating Tarantula- 119mm

Average of all the spiders on the list- 75.1mm

As you can see, the average body size of the venomous spiders is 15.9mm which is 21% of the size of the largest spiders at 75.1mm. So yes, the smaller the spider the more dangerous the spider venom is likely to be. Also, as I tell my students, there is an exception to every rule in biology and the Brazilian wandering spider, which is one of the largest spiders in the world, also has an extremely dangerous venom. What is the reason for this trend you might ask? The answer to that is fairly straightforward. The larger the spider, the more strength it has to overpower its prey and/or opponents. The smaller spiders need the spider venom to make up for the difference in size and strength. For Kumoko the choice was obvious and she goes with the smaller more poisonous spider.

spider venom


The idea that smaller spiders are more venomous as presented in So I’m a spider, So What is actually backed up by some real-world science, so I will be calling this one plausible, as there are some real-world spiders that break the trend.



Just in case you were wondering Kumoko is supposed to be about the size of a piglet, which is far larger than any spider ever found in the real world.


However, it makes sense in context as her “mother” is an enormous spider.

Second Bonus

Further along in the story Kumoko evolves into a spider with sharp sickles on the ends of her forelegs.


As crazy as it sounds, there is a real-world spider called the Trogloraptor that was discovered in a cave in Oregon that has sickles on its forelegs.

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