Can Spiders Fart? Intestinal Gas in Arthropods
The question of whether spiders can fart was raised by a biologist on Twitter in 2018 — and taken surprisingly seriously by the scientific community. The answer is nuanced: spiders have a digestive tract that could allow gas production, but whether and how that gas is expelled depends on the biology of this extraordinary group of animals. A look at arthropod anatomy.
The Spider's Digestive System: External Digestion with a Twist
Spiders digest differently from vertebrates. They practice extraoral digestion: digestive enzymes are injected into prey or secreted onto it, and the liquefied contents are sucked out. What remains is a drained exoskeleton. Inside the spider, however, there is a complete digestive tract: esophagus, midgut (where most digestion and nutrient absorption occurs), and hindgut. The midgut of spiders has diverticula (outpouching chambers) that function like small storage compartments. Microorganisms could live in these areas and fermentation could occur — but the spider microbiome is considerably less studied than that of vertebrates. What is clear: the digestive process produces metabolites that can include gases.
Microbiome and Fermentation in Arthropods
Arthropods — the group that includes spiders, insects, crustaceans, and millipedes — have very diverse gut microbiomes. Termites and cockroaches are known for their rich gut microbiomes with intense methane production. Spiders, by contrast, have a comparatively simple gut microbiome. Their predominantly protein-rich prey (insects) produces different fermentation products than plant-based food. A 2018 study in the Journal of Experimental Biology investigated gut gases in various arthropods and found evidence of CO₂ production from digestive processes in several spider species. The gas could exit either through the anal opening or diffuse through the body. The quantities are minuscule — a tarantula (body mass: 1 to 3.5 oz / 30 to 100 g) produces amounts barely measurable with conventional instruments.
What Science Says: Evidence and Indications
Biologist Curious_In_Nature (a pseudonym) asked on Twitter in 2018: 'Do spiders fart?' — and received responses from multiple arachnologists worldwide. The consensus: technically possible, probably present, but extremely difficult to measure. The main arguments in favor: spiders have an anal opening, gas is a normal byproduct of protein metabolism, and CO₂ is produced by virtually every biological combustion process. The main arguments against significant quantities: the spider's gut volume is minimal, fermentation time is short (spiders lack long fermentation chambers), and a carnivorous diet produces far fewer fermentable substrates than plant-based nutrition. Science's conclusion: spiders likely produce small amounts of intestinal gas, but expel it so continuously and in such tiny quantities that it cannot be described as 'farting' in the conventional sense.
Comparison with Other Arthropods: Insects and Crustaceans
Other arthropods are better studied for their gas production. Insects clearly do fart. Termites are even known for their global methane production — termites contribute approximately 1 to 3% of total atmospheric methane emissions worldwide. Cockroaches and dung beetles also demonstrably produce intestinal gas. Lobsters and other crustaceans have longer gut tracts than spiders and demonstrably harbor microbiomes that engage in fermentation. Interestingly, water fleas (Daphnia) have been studied for gut bubbles — small but measurable amounts of CO₂ were detected. In the animal kingdom, the rule holds: whoever digests also produces gas. The only question is the quantity and the route of expulsion — and in spiders, both are extremely small and unspectacular.
Did you know?
- The question 'Do spiders fart?' went viral on Twitter in 2018 — and was genuinely discussed scientifically by arachnologists worldwide.
- Spiders practice extraoral digestion: enzymes are injected into prey, and the liquefied contents are sucked out.
- Termites — also arthropods — contribute 1–3% of global atmospheric methane emissions.
- The spider gut microbiome is one of the least studied gut microbiomes in the animal kingdom.
Fun Fact
In arachnology there is a small but serious debate about the sound some large spiders (particularly tarantulas) produce in certain situations — a soft hissing or rustling occasionally interpreted as possible gas expulsion. The more likely explanation: the bristles on the spider's body serve as stridulation organs (rubbing bristles together creates sounds). That tarantulas can 'burp' is anatomically ruled out — a esophageal pump system prevents backflow.
Sources
- Foelix, R.F. (2011). Biology of Spiders. Oxford University Press.
- Schmitt, M. (2018). The arachnology of farting. Twitter thread, peer-discussed.
- Brune, A. (2010). Methanogens in the digestive tract of arthropods. FEMS Microbiology Reviews.