Pick a scenario; the sliders stay editable.
Exponential in temperature: every +10 °C multiplies the rate by Q10 = 2. The dot is the current terrarium temperature.
Use Hunt to see a pounce trajectory here (horizontal distance in mm, height in mm).
The science
Metabolism. The standard metabolic rate of a spider scales as SMR = R20 M0.825 Q10(T−20)/10 with R20 = 0.15 mL O2 h−1 for 1 g, Q10 = 2 and 20.1 J per mL O2 (typical orders of magnitude, not a measurement of one animal). A 0.6 g spider at 22 °C burns about 55 J per day at rest; activity multiplies this (rest 1, idle 1.5, web 4, walk 5, hunt 8). Hunger in the HUD is the filled part of an energy reserve that holds 2.5 days of resting metabolism. Spiders are ectotherms: a cold tank slows both energy use and activity.
Prey energy. A house fly is taken as 20 mg wet mass × 6 J/mg × 0.8 assimilation = 96 J (typical values; a ladybird is distasteful and refused). The spider cannot store more than the reserve, so a second fly while full is partly wasted.
Pounce. A jumping spider launches with hydraulic pressure in its legs and no web. Treated as a projectile (1 unit of the scene = 16 mm): for a prey at horizontal distance D and height h, launch angle θ, v2 = g D2 / (2 cos2θ (D tanθ − h)); on level ground the range is v2 sin 2θ / g. The page integrates the flight with RK4 (optional quadratic drag with k = ρCdA/2m ≈ 0.06 m−1, tiny at 0.5 m/s). The available launch speed 0.55–1.0 m/s grows with stamina (an illustrative law). The real jump takes about 0.1 s; the replay is slowed.
Web silk. An orb web has N radial threads and an Archimedean spiral of spacing s: arc length L = (b/2)[F(R/b) − F(r0/b)] with F(u) = u√(1+u2) + asinh u, r = r0 + bθ, b = s/2π. Silk of 2 µm radius (density 1300 kg/m3) weighs only a fraction of a milligram per web, so the main cost is the spider’s own activity (about 6 m of silk per hour is an illustrative building rate). Prey arrive as a Poisson stream with flux φ (insects per m2 per hour, illustrative), so the capture rate is λ = φ A p with sticking probability p = 0.6 and the chance of at least one catch in t hours is 1 − e−λt. A hit thread carries a transverse pulse at c = √(T/μ); for 0.5 mN tension that is a few hundred m/s, so the spider “hears” the fly within milliseconds. (Real jumping spiders mostly hunt by sight and use silk for retreats and draglines; the orb web here is a game element.)
Humidity. Vapour-pressure deficit VPD = es(T) (1 − RH/100) with Tetens es = 0.6108 exp(17.27 T / (T + 237.3)) kPa. The Environment bar combines a temperature optimum (24.5 °C, width 4.5), a humidity band (55–80 %), cleanliness and enrichment; mist raises humidity, which relaxes towards room air.
Needs. Stamina falls with activity and recovers at rest or at night; health relaxes towards a target built from reserves, water, environment and stamina; happiness towards a weighted mean. These weights are game-design choices, not measurements.
Checks. (1) RK4 range vs v²sin2θ/g; (2) energy conservation along the flight; (3) generated spiral length vs the closed form; (4) Q10 ratio and a 24 h bill vs closed form; (5) Poisson capture by Monte Carlo; (6) VPD vs the 20 °C table value 2.339 kPa; (7) string-pulse speed from a finite-difference wave equation vs √(T/μ); (8) a 1440-step day. Simplifications: one spider of 0.6 g, no moulting or breeding, rigid-part leg animation, prices and rewards are illustrative game numbers. Real jumping spiders are kept alone in small ventilated enclosures; this is a learning model, not a care manual.
The spider, insects, log, hideout and leaves are models made in Blender with baked bark maps; the web, physics and game logic run in the page.