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Middle American rattlesnake

🔤 Taxonomy

Crotalus simus is the middle american rattlesnake. The Reptile Database accepts C. simus within the C. durissus complex alongside durissus, culminatus and tzabcan. A 2022 delimitation study synonymised simus under C. durissus, so authorities and collections may disagree. Preserve voucher-quality locality and the taxonomic reference used. Keep exact locality, parentage, photographs and the taxonomic reference with every animal.

📌 Description

A large, robust tropical rattlesnake, commonly 120-160 cm and potentially around 180 cm. It occupies seasonally dry forest, savanna, scrub and agricultural edges. Venom phenotype varies across the broader complex and every bite is a major emergency. This is a medically significant venomous animal for licensed institutional or specialist display only. Apparent calmness, captive breeding and small body size never reduce the protected-contact standard.

📋 Quick reference

Care pointPractical target
Adult size and lifespan120-180 cm; approximately 18-25 years
Adult enclosureAt least 200 x 100 x 100 cm with two lockable shifts
TemperatureAmbient 25-30°C; basking 32-35°C; cool 22-25°C; night 20-24°C
Humidity45-65%; local 60-75% shedding support
FeedingFrozen-thawed whole prey every 14-28 days
SafetyDouble containment, protected contact, trained backup, bite and escape plans

🌍 Distribution

C. simus occurs in southern Mexico (including Oaxaca, Chiapas and Veracruz) through Guatemala, El Salvador, Honduras and Nicaragua to Costa Rica. Older records may use C. durissus, and northern records require distinction from culminatus or tzabcan. Country- or state-level maps cannot resolve habitat patches or revised taxonomic boundaries. Husbandry must follow documented locality rather than colour or a broad trade name.

Range map

⚖️ Legal status

Checked 21 August 2026: C. simus is not listed in CITES, but the whole genus Crotalus is in EU Annex D under Regulation (EU) 2026/1383; Bern is not relevant to its native range. CoP20 Proposal 25 to list most rattlesnakes was rejected in 2025, but that does not override national conservation, collection or dangerous-animal law. Mexico’s NOM-059 list uses C. durissus (Pr) rather than consistently reflecting the current split; other range countries have their own wildlife and venomous-animal rules. Confirm the name accepted on every permit and health plan.

Confirm possession, premises, transport, breeding, sale, import and emergency-notification rules in writing for every origin, transit and destination jurisdiction. Retain permits, invoices, lawful-origin documents, locality, parentage, photographs and the check date.

🤌 Husbandry

House one snake in a restricted venomous room behind a locked secondary barrier. The primary enclosure needs two positively lockable shift hides and protected service access. Follow a written door sequence and isolate and visually confirm the entire animal before opening. A visible tail or rattle does not confirm the head position.

Quarantine for at least 90 days in a robust, simple, fully inspectable enclosure with dedicated tools. Record weight, meals, sheds, faeces, respiration and mouth condition; arrange reptile-veterinary parasite testing according to provenance. House singly except for controlled, professionally planned breeding introductions.

💡 Lighting

Provide 11-13 hours of bright visible light with gradual seasonal adjustment and complete darkness at night. Create a lit basking surface and continuous shaded retreat. All lamps, guards and wiring stay outside primary containment or behind a locked barrier.

Low-output UVB may be offered as a measured Ferguson Zone 1 opportunity. Measure at the highest accessible surface, preserve full shade and prevent contact with a hot guard.

🌡 Heating and temperature

Maintain ambient air at 25-30°C, a limited basking surface at 32-35°C, a cool retreat at 22-25°C and nights around 20-24°C. Measure air and surfaces separately, thermostat and guard every heater and use an independent high-temperature alarm.

Do not heat the entire enclosure or copy exposed field-surface maxima. Seasonal cooling is appropriate only to healthy, established, locality-documented adults where the native climate supports it; never cool juveniles, thin, ill or newly acquired snakes. Tropical or uncertain stock receives no generic brumation.

💧 Humidity and water

Maintain 45-65% ambient humidity with strong cross-ventilation and one ventilated retreat at 60-75% during shedding. Allow surfaces to dry; condensation and stagnant wet substrate require correction.

Provide a stable bowl of clean water through protected access. Monitor drinking, body mass, urates and shed quality. Repeated soaking or dehydration needs a microclimate and veterinary review, not indiscriminate misting.

🌿 Enclosure and decoration

An adult needs at least 200 x 100 x 100 cm. Fit two lockable shifts, clear inspection lanes and an anchored rock/branch structure appropriate to locality. Support heavy décor from the enclosure base and remove fall, crush, pinch and blind-service hazards. Every vent, track and cable hole must contain neonates.

Use 10 cm of low-dust mineral soil with coarse sand and locality-appropriate leaf litter. Avoid loose rock stacks, sharp gravel or wire, aromatic wood and permanently wet substrate. Cleaning must not require dismantling structure around an unconfirmed snake.

🐁 Feeding

Offer appropriately sized frozen-thawed whole prey every 14-28 days, adjusted to weight, build, age, season and provenance. Do not power-feed; ambush predators readily become obese. Whole vertebrate prey needs no routine supplementation.

Feed through a protected port with long tongs and never use live rodents. Confirm the animal behind a locked barrier before retrieving refused prey. Keep permanent weight and feeding records.

🛡 Operational safety and emergencies

Never free-handle, pin, neck or manually restrain for routine work. Use lockable shifts, suitable hooks, transparent shields and protected ports. Two trained adults with assigned roles attend every primary opening. Veterinary procedures require a pre-arranged professional anaesthetic and containment plan.

Before acquisition, give the receiving hospital or poison centre the exact species, locality, facility address and expected adult size. Confirm the regional crotalid antivenom and monitoring pathway. Do not rank risk by reported venom potency, head size or yield: composition and clinical effect vary, and every bite requires urgent hospital assessment. Private antivenom and home administration are unsafe.

After a bite, withdraw, call emergency services, remove constricting items, keep the patient still with the limb neutrally supported and follow poison-centre instructions. Do not cut, suck, ice, shock, massage or apply a tourniquet. Maintain a written escape plan for room isolation, public exclusion, accountability, search zones, secure containers and named decision-makers.

🥚 Breeding notes

The species is viviparous. Large litters are possible; plan conservatively for 15-60 young. Do not mix regional durissus-complex lineages or breed animals with uncertain identity. Pair only documented, locality-compatible adults through shift compartments. Prepare labelled, individual neonate-proof housing and lawful placements before introduction; neonates require the same venom protocol as adults.

🩺 Common problems

  • Obesity and fatty-liver risk from large or frequent meals.
  • Dehydration, retained spectacles or incomplete sheds.
  • Burns and chronic overheating where the cool retreat fails.
  • Respiratory disease after stagnant moisture or inappropriate cooling.
  • Falls, crushing or abrasion from unstable décor.
  • Mites, internal parasites and stomatitis, especially in wild-origin stock.
  • Taxonomic or provenance loss that compromises legal, medical and breeding decisions.

Hands-on home treatment is unsafe. Lock the animal into a shift and use an experienced reptile veterinarian.

📌 Conclusion

The middle american rattlesnake belongs only in a licensed programme able to preserve locality, engineer secure shifts, work entirely through protected contact and maintain rehearsed hospital and escape responses.

📚 Sources and further reading