ants/docs/NEST-BUILDING.md

NEST BUILDING AND COLONY ARCHITECTURE

research notes for informing ant farm simulation behavior. sources cited inline.

INITIAL NEST FOUNDING

after a mating flight, a queen sheds her wings, finds a suitable spot, and digs a "founding chamber" -- a small cavity just big enough to tend eggs and larvae. she seals the entrance and doesn't leave until the first workers emerge. she feeds larvae with trophic (unfertilized) eggs laid specifically as food.

founding chamber size: ~24 cm^2 in Camponotus fellah studies.

what triggers digging location: queens prefer softer, more humid soil. in shaded habitats (less dense, more humid soil), queen establishment was greater, nest depth was greater, and excavated volume was greater. soil density and humidity are the primary abiotic factors.

[eLife: colony demographics shape nest construction] [Wiley: soil density and humidity in leaf-cutting ant queens]

TUNNEL ARCHITECTURE

shape transition: ants first excavate a circular chamber. once it reaches a critical area, buds appear along the chamber wall and tunnels branch off. this is a density-driven phase transition:

high ant density along wall = uniform digging (chamber grows) low ant density per unit wall = localized instabilities = tunnels branch

this is the key insight from Toffin et al. (PNAS 2009).

tunnel descent angle: ants dig at roughly the angle of repose of the substrate (~40 degrees for typical sand). they don't exceed this -- "if I'm a digger, my digging technique is going to align with the laws of physics, otherwise my tunnels collapse and I die." (Caltech/PNAS 2021)

branching complexity increases with population size. new tunnels branch from existing tunnel walls, not just from chambers.

moisture influence: tunnels extend vertically until hitting either the surface or a soil layer with sharply increasing water content. ants excavate more in moist soil but stop ~12mm above water-saturated layers.

gravity's role: gravity promotes vertical motion and accounts for the formation of ellipsoidal chambers and vertical tunnels. it acts as a "template" for tunnel direction.

[PNAS: shape transition during nest digging in ants (Toffin 2009)] [PLOS ONE: role of colony size on tunnel branching] [PNAS: unearthing real-time 3D ant tunneling mechanics (2021)] [Nature Sci Reports: ant nest architecture shaped by temperature] [PMC: soil moisture and excavation behaviour]

DIGGING MECHANICS

ants carry particles one at a time in their mandibles. they prefer smaller grains. most effective excavation occurs when grains are small enough to carry.

why tunnels don't collapse: intergranular forces decrease around ant tunnels due to "granular arching" -- force chains in the soil redistribute around the tunnel, forming natural arches. any grain an ant picks from the tunnel face is already under low stress due to this force relaxation. ants achieve stability without reinforcements purely by benefiting from physics. the arch structures have a greater diameter than the tunnel itself.

digging pattern: piecewise linear tunnel segments. ants dig in short straight stretches, then change direction slightly.

excavated material deposition: ants carry grains to the surface and deposit them near the nest entrance, forming a mound/midden. in Pheidole oxyops, the pile forms a crescent shape ~13cm from the entrance. 82% of grains stay where dropped; 18% roll downhill. in leaf-cutter ants, soil pellets are transported sequentially over 2m involving up to 12 workers in a relay chain.

[PNAS: ants make efficient excavators] [ResearchGate: sand pile formation in Dorymyrmex ants] [PLOS ONE: sequential soil transport in leaf-cutting ants]

DIVISION OF LABOR IN CONSTRUCTION

age polyethism: young ants do most of the digging. older ants forage more.

young vs old digging style: young ants dig slanted tunnels. old ants dig straight down. this is a form of age polyethism where age dictates not just task likelihood but task execution style.

emergency override: after a nest catastrophe (collapse, flooding), all ants dig regardless of age to restore lost nest volume.

queen's role: digs only during founding. once first workers emerge, she never digs again. focuses exclusively on reproduction. her pheromones influence colony-wide behavior including construction coordination.

coordination: no central planning. workers follow chemical markers ("building pheromone") on substrate indicating active construction zones. substrate vibrations may also coordinate digging underground.

[eLife: colony demographics shape nest construction] [Springer: task allocation in ant colonies] [Knowable Magazine: evolution of division of labor]

COLONY GROWTH AND NEST EXPANSION

scaling: nest volume grows logistically to a saturation volume that scales linearly with population size. larger colony = proportionally larger nest.

timing: population increase is followed ~15 days later by an increase in excavated area. nest expansion lags population growth by roughly one week. the nest is excavated in discrete digging episodes triggered by population increases.

expansion pattern: three simultaneous processes:

1. nest deepening (main shaft extends)
2. chamber magnification (existing chambers enlarge)
3. creation of new vertical chamber sequences (new branches)

trigger: population crowding. track (colony population) / (excavated area). when this exceeds a threshold, digging episode begins.

[eLife: colony demographics shape nest construction] [bioRxiv: colony demographics shape nest construction (preprint)]

ANT FARM (2D) SPECIFICS

the formicarium was invented by Charles Janet (French entomologist) -- reducing 3D nest architecture to virtual 2D between two panes of glass.

the gap between panes should match the diameter of the species' typical burrow, so no soil layer sticks to the glass. forces all tunneling to be visible.

climbing on glass: ants CAN walk on vertical glass surfaces. they use adhesive pads (arolia) on legs above their center of mass (pulling) and dense tarsal hair arrays on legs below center of mass (pushing). anti-escape coatings (PTFE, petroleum jelly) are used on formicarium rims specifically because ants climb glass easily.

gravity in 2D: ants walk on the glass surface while digging in substrate between the panes. sand/soil is subject to gravity and will collapse if not supported. the angle-of-repose constraint still applies.

behavioral differences: ants exhibit the same chamber-first-then-tunnel transition, same density-driven branching, same age-based digging allocation in 2D as 3D. the main difference is the architecture is forced planar.

[Wikipedia: formicarium] [AntKeepers: classic ant farm] [PLOS ONE: on heels and toes -- how ants climb]

WITHOUT A QUEEN

survival: 3-4 months typical, up to 12 months in good conditions.

behavioral changes: workers search for the missing queen. stress increases. aggression increases (queen pheromones normally maintain harmony). social organization deteriorates.

still dig? yes. workers continue to excavate, reinforce, and maintain the nest.

reproduction: some workers begin laying unfertilized eggs (males only). in some species, workers engage in dominance tournaments and winners become "pseudoqueens" with dramatically increased lifespans (7 months to 4 years).

no new workers: colony cannot produce workers without a queen. slow decline. no larvae also means nutrition problems since larvae help digest solid food for the colony.

[MisfitAnimals: how long do ants live without a queen] [BestAntsUK: ant farm essentials -- how crucial is a queen] [NYU: dueling ants vying to become replacement queen]

EMERGENT PATTERNS AND STIGMERGY

stigmergy: indirect coordination through environmental modification. an ant's action changes the environment, which stimulates the next ant's action. no direct communication needed. coined by Grasse (1959) studying termites.

building pheromone: ants deposit a pheromone on building material/substrate. this has a limited lifetime, creating a spatially heterogeneous "topochemical landscape." areas with fresh pheromone attract more building/digging activity. without pheromone dynamics, no coherent structure can be built in simulations. (Khuong et al., PNAS 2016)

pheromone lifetime is key: controls the growth and form of nest architecture. short lifetime = more localized construction (tight tunnels) long lifetime = more diffuse construction

template + stigmergy hybrid: two interactions coordinate building:

1. stigmergic: building pheromone on substrate
2. template-based: ants use body size as cue to control tunnel/chamber dimensions (e.g. roof height)

density-driven transitions (restated): high local ant density = chamber expansion. low local density = tunnel formation. the chamber-to-tunnel transition emerges from this simple density rule.

simple rules produce complex nests. the combination of: a. building pheromone deposition/decay b. local density sensing c. gravity alignment d. body-size templates produces the full range of observed nest architectures. no ant has a blueprint.

[PNAS: stigmergic construction and topochemical information (Khuong 2016)] [Wikipedia: stigmergy] [PNAS: shape transition during nest digging (Toffin 2009)] [eLife/PMC: emergent regulation of ant foraging]

SIMULATION PARAMETERS (DISTILLED)

key values that map to tunable config/uniforms:

tunnel descent angle ~40 degrees (angle of repose of substrate) chamber-tunnel transition ant density per unit wall drops below threshold building pheromone decay controls architecture compactness nest volume / population linear scaling, ~24 cm^2 per founding queen young ant digging bias slanted tunnels vs vertical (age polyethism) material deposit location near surface entrance, biased away from it grain removal rate one grain per trip, prefer lighter grains expansion trigger population / excavated area exceeds threshold moisture preference dig toward moist, stop before saturated

the ant presence texture (already exists as stub) combined with a digging pheromone channel would give us the chamber-then-tunnel transition for free.