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What varieties of spider / caterpillar(?) are these? And what is the spider doing to the caterpillar? This is in Texas.

This went on for hours, with the spider dancing with the caterpillar in the spider web where the caterpillar was caught. After 10+ hours, this morning, I found the caterpillar -- still intact -- curled up on the ground beneath. Was the spider sucking the juice out of it or something? I don't understand what parts of it, if any, was consumed by the spider.

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  • $\begingroup$ Are you aware how spiders eat? $\endgroup$
    – DKNguyen
    Jun 28 at 17:19
  • $\begingroup$ @DKNguyen Probably not by sucking the juices/blood out of its prey like a mosquito? Which is why I was particularly confused, as the spider didn't seem to be 'eating' it. Now the caterpillar is just dead. So I'm not sure what the spider did to it.. $\endgroup$
    – ajfbiw.s
    Jun 28 at 19:35
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    $\begingroup$ Not like that no. I assume you're younger if you're not aware, but they do drink their victims. Spiders pump digestive enzymes into the prey to externally digest it then drink it, whereas you ingest your prey and the digestion is done internally. $\endgroup$
    – DKNguyen
    Jun 28 at 19:36
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    $\begingroup$ Thanks! I did not know this. I also looked this up just now, and yes, that's in fact what happened: "When feeding the spider regurgitates enzyme rich stomach fluids over and into its prey. This external digestion... reduces the prey's body and tissues to a chitinous soup. The liquid is sucked up through the spider's tube-like mouth, aided by the action of the pumping stomach, leaving the hard parts behind. Spiders... inject digestive fluids into the bitten prey and suck out its liquefied internal tissues, leaving an almost intact body husk behind." (src: australian.museum) @DKNguyen $\endgroup$
    – ajfbiw.s
    Jun 28 at 22:45

2 Answers 2

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The spider is a cobweb weaver - family Therididae (can be determined from the bulbous abdomen, thinness of legs and small cephalothorax) and appears to be Steatoda triangulosa from the brownish colour, white markings on the abdomen, and rings/annulations on the legs. S.triangulosa is found widely across North America and Europe.

The prey is not a caterpillar but a myriapod, I believe in the order of flat-backed millipedes.

As @DKNguyen already answered, the spider was preying on the millipede. The 'dancing around' was the spider trying to subdue the prey by wrapping it up in silk, but for prey that size, it takes a long time to get enough silk on it to hinder its movements.

Once the spider gets a meal out of the prey, they detach it from the web and let it fall to the ground below. This is often a way to detect when you have a cobweb spider in a corner or under a stair or something - when you see a clutter of dead bugs. The clutter also tells you that the spider is helping take care of pest control while staying in one spot.

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Spiders pump digestive enzymes into the prey to externally digest it then drink it, whereas you ingest your prey and the digestion is done internally.

That's not even the only way animals eat...starfish bring their stomachs out of their body onto their prey and digest the prey there. Might seem even weirder, but arguably less roundabout than the spider's method.

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  • $\begingroup$ I dunno about that. Regurgitating your stomach to surround a victim outside of your body would seem to be a very risky proposition; it could be damaged. I’ll take my meal with a straw, please, like the early astronauts. $\endgroup$ Jun 30 at 14:16
  • $\begingroup$ @anongoodnurse I think it is less like a straw and more like throwing up on your food, letting it sit and then drinking it up. $\endgroup$
    – DKNguyen
    Jun 30 at 14:18
  • $\begingroup$ Ooooo, that does sound awful indeed, but safer for keeping my stomach out of harm’s way. I saw this once at a tiny aquarium in Maine. Fond memories! (Ugh.) $\endgroup$ Jun 30 at 14:32

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