A spider cannot chew a fly the way you chew food. Instead, it bites the fly, pumps digestive enzymes into its body (or onto it), and then sucks up the resulting liquid, leaving a dry, crumpled husk behind. This is called external digestion, and it is how nearly every spider eats.
Step by Step: How a Spider Eats a Fly
- Catch. Web-builders feel the fly’s struggles through vibrations in the silk. Hunting spiders, such as jumping spiders, stalk or ambush it.
- Bite and subdue. The spider bites with its fangs (the tips of its chelicerae) and injects venom. For a fly, the venom works fast and the struggling stops within seconds.
- Wrap (some species). Many web-builders spin silk around the fly. This keeps it from escaping and lets the spider save it for later.
- Add digestive fluid. The spider releases digestive enzymes into the fly’s body or over it. The enzymes break down soft tissue into a nutrient-rich soup.
- Crush and suck. The spider works the fly over with its mouthparts, which crush and squeeze it, while a muscular sucking stomach draws the liquid in. Fine hairs around the mouth filter out solid bits, because a spider can only swallow liquid.
- Discard. What is left is the fly’s dry exoskeleton, often rolled into a little ball and dropped from the web or left behind.
How Long Does It Take?
It varies with the spider and the size of the meal. A small fly can take anywhere from several minutes to an hour or more, and some spiders pause, rest, and return to a wrapped meal later. Bigger prey takes longer.
Do Spiders Have Teeth?
No. Spiders have fangs for injecting venom and rough mouthparts for squeezing prey, but no teeth for chewing. That is why they need to turn their food into a liquid first.
Does a Spider Always Wrap Its Prey?
No. Orb weavers and cobweb spiders (like the common house spider) often wrap prey in silk. Hunting spiders, like jumping spiders and wolf spiders, usually do not use a web at all. They chase or pounce, bite, and start feeding straight away.
Is It Dangerous to Us?
The spiders you find eating flies in your home are almost always harmless to people. Their venom is built for insects. A very small number of species worldwide, such as the black widow and brown recluse, can be medically significant. If you are bitten and have swelling, pain that is getting worse, or any unusual symptoms, call your doctor or local poison control line.
What If I Want to Feed a Pet Spider?
Pet spiders eat the same way. You offer live prey and the spider does the rest. Our guides cover the details for specific species:
Remove any uneaten live prey after a day or so, since some insects can bother a resting or molting spider.
Bottom Line
A spider eats a fly by biting it, dissolving its insides with digestive enzymes, and drinking the liquid. It never chews, and what remains is an empty shell. If you want to see it in action, a web in the corner of a window is the best place to watch.
