Roughly speaking, a small, complex electronic circuit or IC might sit in "sleep mode" using a current of roughly 1 µA (e.g. 1, 2), thereby using roughly $3\times 10^{-6}$ Watts, and that converts to roundly $2.5\times 10^{-6}$ kcal/hour or $62\times 10^{-6}$ kcal/day.
I suppose you could call that 62 micro-kcal/day or 62 milliCalories/day.
One day I noticed a small spider in my home, sitting in its small web, and kept an eye on it. After several weeks of watching I hadn't seen it catch anything. I slightly perturbed the web and it reacted. It was still alive.
Question: I'm curious to know roughly how much energy a small spider needs to sit and wait. Might this be termed roughly the spiders Basal metabolic rate? It could be for any small spider that spends much of its time waiting for prey. As long as an approximate size or mass is available then it could be expressed as kcal/day/kg or some similar unit.
I have read about Kleiber's law in this answer, but I don't think it is meant to extend down to small spiders.
note: I'm just asking for the energy expended during resting periods. Of course during a day the spider may do web maintenance, catch or eat prey, but it's the resting rate of energy consumption, on a daily basis, that I'm asking about.