Some assassin bugs, most famously Acanthaspis petax, pile the drained exoskeletons of prey (ants, termites) on their backs after feeding — a documented anti-predator tactic ("backpacking") that visually breaks up the bug's outline for hunting predators such as jumping spiders. This lab turns that into two competing real curves instead of decoration:
P_detect(L) = P0 · e^(−k·L) (detection probability per encounter)
v(L) = v0 · max(0.2, 1 − p·L) (movement speed)
Survival = 1 − detections / encounters (running Monte-Carlo estimate)
L is the disguise load (carcasses carried), P0 the baseline chance an undisguised bug is spotted per predator encounter, k the exponential decay rate at which extra carcasses degrade a predator's ability to recognise the bug's shape, and p the per-carcass speed penalty from the added mass and bulk. Every simulated encounter between the bug and a patrolling predator rolls against P_detect(L); a detection has a fixed 80% chance of being a successful strike, ending the run. The panel compares the closed-form P_detect(L) against the empirical detections/encounters ratio measured live, and tracks foraging efficiency (prey eaten per simulated minute) — which falls as speed falls, because a slower bug reaches fewer of the food items scattered in the arena.
- Disguise load and speed penalty are the direct tradeoff: more camouflage, less mobility.
- k controls how quickly each additional carcass helps — a high k means even a small pile is very effective.
- Predator count and P0 set predation pressure independently of the bug's own strategy.