# Ant Pheromone Biology Reference doc on ant pheromone types, chemistry, triggers, and environmental factors. Organized for simulation design — what matters for modeling, what the real biology says, and where the data is thin. ## Pheromone types ### Trail pheromones Guide nestmates to food, new nest sites, or other resources. Encode distance and quality information through concentration gradients. Gland sources vary by subfamily: - Poison gland (most Myrmicinae — stinging ants) - Dufour's gland (most Formicinae — non-venomous ants) - Pygidial gland, sternal glands, hindgut (various) Known compounds by species: species compound gland Atta texana, A. cephalotes methyl 4-methylpyrrole-2-carboxylate poison Atta sexdens rubropilosa 3-ethyl-2,5-dimethylpyrazine poison Tetramorium caespitum 70:30 2,5-dimethylpyrazine + EDMP poison Tetramorium meridionale indole (major) + 4 pyrazines poison Monomorium pharaonis (E,E)-faranal poison Myrmica spp. EDMP + homofarnesenes poison + Dufour's Solenopsis invicta various poison Volatility is a feature — trails evaporate in minutes to hours, so paths to depleted food naturally fade. The evaporation rate is effectively the colony's spatial memory duration. ### Alarm pheromones Fast-acting signals that trigger either panic (flee) or aggression (attack) depending on species, colony size, and context. Triggers: - Physical disturbance of nest or individual - Predator detection (olfactory, visual, or tactile) - Crushing/injury of nestmates (damaged ants release alarm compounds) - Intrusion by non-nestmates Known compounds: compound species gland 4-methyl-3-heptanone Atta, Pogonomyrmex, Ooceraea mandibular formic acid Formica, Camponotus poison n-undecane Camponotus, many Formicinae Dufour's 2-heptanone Iridomyrmex pruinosus mandibular 3-octanol Acromyrmex echinatior mandibular 3-octanone Acromyrmex octospinosus mandibular (S)-(-)-citronellal Platythyrea punctata mandibular (S)-(-)-actinidine Platythyrea punctata mandibular Behavioral response sequence: stop movement -> swing antennae -> alerted posture -> species-specific response (flee or attack). Larger species and larger colonies tend toward aggression; smaller species tend toward evacuation. #### Carpenter ant alarm system (formic acid + n-undecane) Two-component blend from two different glands: - Formic acid (poison gland) -> avoidance behavior, move away from source - n-Undecane (Dufour's gland) -> attraction toward source, approach to attack Each component alone produces a distinct response. Together they create the full alarm sequence: alert, then approach and aggress. Formic acid also modulates nestmate recognition — puts ants into a heightened discriminatory state where they're more likely to attack non-nestmates. Processed in ~5 specific "alarm-sensitive" glomeruli clustered in the dorsalmost part of the antennal lobe, relayed to the lateral horn. #### What triggers alarm? Plants? Predators? No strong evidence for specific plants that trigger false alarm responses, though some alarm compounds (citronellal) are also found in plant oils, so cross-reactivity is plausible. Some alarm compounds (citral, 2-heptanone, 4-methyl-3-heptanone) have antifungal properties, suggesting a dual role in pathogen defense — the alarm system may have originally evolved as an antimicrobial response. Main natural triggers are physical: nest disturbance, predator contact, and injured nestmates releasing their contents. The "danger zone" concept maps best to areas where nestmates have been injured or where persistent threats exist, not to specific environmental chemicals. ### Repellent / negative pheromone Deposited at trail junctions leading to unrewarding branches. Prevents the colony from getting stuck on depleted food. Key details from Pharaoh's ant studies: - Lasts ~2x longer than attractive trail pheromone (~78 min vs ~33 min) - Ants encountering it U-turn or zigzag - Deposited specifically at bifurcation points, not along entire failed paths Source: Nature 438, 442 (2005) ### Queen pheromones Complex, multifunctional. Known effects: - Attract workers for queen attendance - Promote brood care - Induce nestmate discrimination - Inhibit larval sexual development (through worker behaviors) - Suppress reproduction in other queens and workers - Induce worker policing of reproductive workers - Mediate queen acceptance/rejection in polygyne colonies Chemistry is poorly characterized compared to trail/alarm pheromones. Involves cuticular hydrocarbons and at least one dedicated odorant receptor (HsOr263 in Harpegnathos saltator). Difficult to isolate because the signal may be a complex blend rather than a single compound. ### Necrophoresis / death pheromones Trigger corpse removal for nest hygiene. Dual-signal system: 1. Loss of "life signals": living ants produce dolichodial and iridomyrmecin on their cuticle. These disappear within ~60 minutes of death. Their absence is the initial trigger. 2. Gain of "death signals": oleic acid and linoleic acid accumulate as the corpse decomposes. These are the classical necrophoresis triggers. Timing: only 15% of freshly killed corpses get removed. Rises to 80% for corpses 1-6 days post-mortem as fatty acids accumulate. The colony doesn't panic-clean — it waits for chemical confirmation. ### Propaganda pheromones Used by slave-making (dulotic) ants during raids. Polyergus queens enter Formica host nests, kill the resident queen, acquire her chemical profile, and release substances from an enlarged Dufour's gland that reduce worker aggression. Raiding workers release: - Manipulative alarm signals (cause panic, disorganized defense) - Chemical weapons (directly repellent) - Appeasement substances (reduce aggression toward the raider) Stolen brood are chemically imprinted after eclosion, causing them to identify the slave-maker colony as home. ### Cuticular hydrocarbons (CHCs) — colony recognition Not classical volatile pheromones but contact chemicals on the cuticle. Each colony has a distinctive CHC profile — a blend of dozens of hydrocarbons that workers learn and use to distinguish nestmates from non-nestmates. Non-nestmates are attacked. The postpharyngeal gland stores and distributes CHCs, homogenizing the colony odor through trophallaxis (food sharing). ### Recruitment pheromones Functionally distinct from trail pheromones in some species. In Leptogenys diminuta, two gland sources serve different roles: - Poison gland secretions: orientation cues (where to go) - Pygidial gland secretions: recruitment stimulus (leave the nest and follow) This separation means "follow this path" and "come help" are independent signals that can be modulated separately. ### Brood pheromones Signals from eggs, larvae, and pupae that attract worker care. Help workers assess developmental stage and nutritional needs. Part of the demand chain that links larval nutritional needs -> nurse behavior -> forager food preferences. Less well-characterized than adult pheromones. ### Sex / mating pheromones Released by virgin queens (gynes) to attract males during nuptial flights. Less studied than other types. Identified in Polyergus breviceps. ## Food quality ### What "quality" means to ants Primarily macronutrient content — the protein-to-carbohydrate (P:C) ratio. Different colony members need different things: - Workers need carbohydrates (energy for foraging, maintenance) - Larvae and queens need protein (growth, egg production) - Foragers collect for the colony's current needs, relayed through a demand chain: larvae -> nurses -> foragers Sugar concentration is the primary quality axis for foraging workers. In the key Pharaoh's ant study, 1.0 M sucrose = "high quality" and 0.01 M sucrose = "low quality." Species-specific sugar preferences exist — carpenter ants (Camponotus modoc) and European fire ants (Myrmica rubra) show selective preferences for specific mono-, di-, and trisaccharides. Not all sugars are equal. ### How ants assess quality Two mechanisms: 1. Contact chemoreception — tasting with mouthparts and antennae 2. Post-ingestive feedback — evaluating nutritional content after consumption Colony-level nutritional regulation follows a "geometric framework" model: colonies actively balance P:C intake, shifting forager preferences based on current deficits. A protein-starved colony will recruit more aggressively to protein sources. ### How quality modulates pheromone deposition The Pharaoh's ant study (Jackson, Holcombe & Ratnieks 2004/2007): - Trail marking occurs at ~40% frequency among both fed and unfed foragers - High quality food (1.0 M sucrose) -> significantly more high-intensity continuous marking - Low quality food (0.01 M sucrose) -> no significant difference in marking intensity between fed and unfed ants - This is a graded individual response — ants modulate marking intensity, not all-or-nothing Contrast with Lasius niger, where trail strength modulation IS all-or-nothing at the individual level — an ant either marks or doesn't, based on quality. The difference: Pharaoh's ants live in dark enclosed spaces and rely heavily on pheromone trails, so they must always produce some trail. L. niger can use visual orientation and afford to skip trail-laying entirely for poor food. Ants also adjust deposition based on environmental uncertainty — they modulate trail marking in response to changing conditions and their error probability (Czaczkes et al. 2015). ### Simulation relevance For the sim, food quality maps to a 0-255 value stored in cell metadata bits. When an ant picks up food, it reads the quality and stores it as cargoQuality. The deposition multiplier would scale pheromone output — high quality food gets stronger trails, attracting more ants. The colony naturally converges on the best source first, then shifts when it depletes. "Different types of food" is less important than "different concentrations." Real ants care about sugar molarity and protein content, not food identity. For the sim, a single quality scalar captures the essential dynamics. ## Pheromone detection ### Olfactory receptor genes Ants have 300-500 odorant receptor (Or) genes — 4-5x more than most insects (Drosophila has ~60). This expansion predates complex sociality but facilitated it. A specialized 9-exon Or gene subfamily detects cuticular hydrocarbons and candidate pheromones. ### Antennal lobe glomeruli Each Or gene roughly corresponds to one glomerulus in the antennal lobe. species glomeruli count Apterostigma cf. mayri ~630 Camponotus (carpenter) ~430-460 Apis mellifera (honeybee) ~163 Drosophila melanogaster ~43 Workers have more glomeruli than males, reflecting greater need for chemical discrimination. Worker and queen antennal lobes differ in composition and Or expression. ## Environmental effects on pheromones ### Temperature High temperatures accelerate degradation. Above ~40C, workers cannot discriminate previously-marked substrate. Above ~30C, foraging activity drops partly because trails decay too quickly to be useful. Different compounds have different thermal stability: in Tapinoma nigerrimum, most gaster secretions vanished at 25C, but iridodials persisted up to 55C. Aphaenogaster senilis secretions resisted elevated temperatures better. Pheromone persistence = f(temperature, time since deposition). Both interact — higher temperature accelerates decay at all time points. ### Humidity Higher humidity slows evaporation of polar pheromone components. Specific experimental data is sparser than for temperature. The effect is real but less dramatic than temperature in most contexts. ### Substrate surface Porous surfaces absorb pheromone and release it slowly (longer persistence). Smooth impermeable surfaces allow faster evaporation (shorter persistence). Direct experimental data on ants is thin — the Pharaoh's ant study (~9 min on plastic, ~3 min on paper) is one of the few quantitative comparisons. The physics is well understood but species-specific measurements are rare. ### Volatility as design feature Trail pheromone volatility provides automatic negative feedback — trails to depleted food fade without any active erasure. The evaporation rate sets the colony's spatial memory duration. Too fast = no useful trails. Too slow = colony gets stuck on depleted paths. Evolution tuned this balance per species and habitat. ## Colony-level dynamics ### Colony size effects Larger colonies have higher collective response thresholds. The relationship is driven by social feedback — short-range excitatory and long-range inhibitory interactions. In army ants, increasing colony size causes a qualitative behavioral shift: organized search patterns in small colonies give way to spontaneous mass raids in large ones. Per-capita interaction rate is roughly scale-invariant — connectivity scales hypometrically with colony size. ### Colony state modulates pheromone dynamics - Protein-starved colonies shift forager preferences toward protein, changing trail deposition patterns (more intense marking to protein sources) - Carbohydrate-rich diets increase social immunity - Weakly volatile "aggregation" pheromones mark the nest site as a constant baseline signal anchoring the colony spatially ### "Colony mood" Not a scientific term, but maps onto real dynamics: - Alarm state propagates as more individuals detect alarm compounds and release their own (positive feedback cascade) - Foraging motivation modulated by colony nutritional state — hungry colonies produce stronger recruitment signals - The exploration/exploitation balance shifts with colony experience and environmental conditions ## Sources Pharaoh's ant pheromone modulation Jackson, Holcombe & Ratnieks 2004/2007 ScienceDirect S0003347207002278 Negative pheromone Nature 438, 442 (2005) Alarm pheromone processing (carpenter ants) PMC2912167 Alarm pheromone in clonal raider ant PMC9941220 Formic acid + nestmate recognition J Exp Biol 224(20) jeb242784 Necrophoresis dual signals PNAS 0901270106 Corpse chemical changes J Chem Ecol 10.1007/s10886-013-0365-1 Slave-maker chemical warfare PLOS ONE 10.1371/journal.pone.0147498 Queen pheromone properties Behav Ecol Sociobiol 10.1007/s00265-023-03378-8 Trail pheromone review Morgan 2009, Physiological Entomology 10.1111/j.1365-3032.2008.00658.x Trail pheromone compound list Natural Product Communications 10.1177/1934578X1400900813 Odorant receptors in social insects Nature Communications 10.1038/s41467-017-00099-1 Pheromone-sensitive glomeruli Proc R Soc B 10.1098/rspb.2006.3565 Olfactory system review PMC8002415 Ant olfactory receptor expansion Vanderbilt (2012) Temperature effects on trail following J Chem Ecol 10.1007/s10886-012-0130-x Colony interaction scaling Frontiers in Ecology and Evolution 10.3389/fevo.2022.993627 Collective sensory threshold PNAS 10.1073/pnas.2123076119 Ant nutritional ecology ScienceDirect S221457451400090X Nutrient regulation Myrmecological News (Csata & Dussutour 2019) Exocrine glands of ants Chemoecology 10.1007/BF01256548 Sugar preferences PMC8371376 Pheromone deposition under uncertainty Czaczkes et al. 2015, PMC4590477