How we check

Every verdict on this site comes from two things: open occurrence records counted from GBIF and a published range for each species. Here is how they fit together and where they fall short.

The records

GBIF, the Global Biodiversity Information Facility, pools records from museums, universities, state agencies and observation platforms such as iNaturalist. For each species we ask the GBIF API for US records and count them by state, county and month. Data downloaded October 25, 2026.

We keep only records published under CC0 or CC BY 4.0. That is 295,046 of 982,541 US records for the species we track. The rest, mostly iNaturalist photos under a non-commercial license, are left out, so our counts are lower than the totals you see on gbif.org. Zoo animals, fossils and records GBIF flags as having coordinate problems are left out too.

Most records carry coordinates, and GBIF places them in a state and county itself. For older records with only a written state name, we read the name and fix the usual variants, such as "Ohio (OH)", "Nv" or "Tex.". Names we cannot place with confidence, like county names alone, are dropped.

Lives here, rare records, gone

A record only says that someone saw or collected the animal once. Snakes get carried in hay and cargo, spiders ride in boxes and pets escape. So a single record does not make a state part of the range. We use these rules:

• Snakes and the Gila monster: we keep a reviewed list of states for each species, checked against state wildlife agencies, university herpetology programs and museum collections. A state on that list gets "Lives here". A state off the list with open records gets "Rare records", with the count and the year of the latest record.
• Spiders, scorpions and centipedes: published range maps are rough, so the records decide. A state gets "Lives here" when there are records from 3 or more counties, or 20 or more records, or 5 or more records from at least 2 counties. Fewer records give "Rare records". Black widows are the exception: their three species together cover the lower 48 states, which we take from published ranges because open records are thin in the North.
• "Gone" means the species is documented as having disappeared from a state, like the timber rattlesnake in Maine and Rhode Island.
• One or two records far from the range, in a state that does not even border it, are treated as captive animals or mislabeled specimens. Those states get "Not here", and the page still shows the record count.
• "Not here" otherwise means no open records and outside the range. It is not proof of absence.

Take the brown recluse in Michigan. Open data holds a single record from the state. Michigan is far outside the recluse's range, so the page says "Rare records" and shows that one record instead of a yes or a no.

Old names

Snake names have changed. Records once filed as the prairie rattlesnake, Crotalus viridis, include western rattlesnakes from California to Washington, and old eastern massasauga records include the western species. For these, we skip the states where the records belong to the other species:

• Prairie rattlesnake: records from CA, NV, WA, OR, ID, UT are not counted.
• Eastern massasauga: records from TX, AZ, KS, OK, NE, NM, MO, CO are not counted.
• Western massasauga: records from OH, IA are not counted.
• Eastern coral snake: records from TX are not counted.

Where herpetologists split a species recently, we count the parts together and say so on the species page: copperheads include the broad-banded copperhead, cottonmouths include the Florida cottonmouth, and western rattlesnakes include five forms.

Maps and months

County maps count the venomous species with at least one open record in each county. Empty counties usually mean nobody has published a record, not that the animal is missing. Month charts show when records were made. People go outdoors more in summer, so the charts mix animal activity with human activity.

What we do not do

We do not give medical advice. For any bite or sting, call 911 or Poison Control at 1-800-222-1222. We do not invent facts: if we have no data for a block, the block is not shown. Text on the site is written from the records and the sources below.

Sources

Records: GBIF.org (2026), GBIF Occurrence Data via the GBIF occurrence API, 203 datasets. The list of datasets with record counts is in gbif-datasets.csv. Largest contributors:

• iNaturalist Research-grade Observations, iNaturalist.org. doi:10.15468/ab3s5x (69,795 records)
• University of Michigan Museum of Zoology, Division of Reptiles & Amphibians, University of Michigan Museum of Zoology. doi:10.15468/g3bard (16,436 records)
• AMNH Herpetology Collections, American Museum of Natural History. doi:10.15468/jfkgyh (13,826 records)
• NCSM Herpetology Collection, North Carolina State Museum of Natural Sciences. doi:10.36102/dwc.3 (13,536 records)
• NMNH Extant Specimen Records (USNM, US), National Museum of Natural History, Smithsonian Institution. doi:10.15468/hnhrg3 (13,275 records)
• LSUMZ Herps Collection, Louisiana State University Museum of Natural Science. doi:10.15468/iogakq (11,778 records)
• KUBI Herpetology Collection, University of Kansas Biodiversity Institute. doi:10.15468/ubdwdc (10,561 records)
• SDNHM Herpetology Collection, San Diego Natural History Museum. doi:10.15468/tacqs9 (9,746 records)
• Distribución potencial de las especies de anfibios y reptiles en categoría de riesgo de México, Comisión nacional para el conocimiento y uso de la biodiversidad. doi:10.15468/mdqurs (9,201 records)
• Biodiversity Research and Teaching Collections - TCWC Vertebrates, Texas A&M University Biodiversity Research and Teaching Collections. doi:10.15468/szomia (8,257 records)
• CM Herps Collection, Carnegie Museums. doi:10.15468/lxe6h4 (7,608 records)
• TNHC Herpetology Collection, University of Texas at Austin, Biodiversity Collections. doi:10.15468/xrorih (5,914 records)
• Auburn University Museum of Natural History Herpetology Voucher Collections, Auburn University Museum. doi:10.15468/d1vglq (5,588 records)
• UTA Reptiles, University of Texas-Arlington. doi:10.15468/mlehrb (5,587 records)
• Herps Specimens, Illinois Natural History Survey. doi:10.15468/74ijg4 (5,164 records)
• Field Museum of Natural History (Zoology) Amphibian and Reptile Collection, Field Museum. doi:10.15468/u2pzhj (4,890 records)
• MVZ Herp Collection (Arctos), Museum of Vertebrate Zoology. doi:10.15468/pi1mts (4,769 records)
• CHAS Herpetology, Chicago Academy of Sciences. doi:10.15468/9lim5m (4,712 records)
• CAS Herpetology (HERP), California Academy of Sciences. doi:10.15468/bvoyqy (4,599 records)
• LACM Vertebrate Collection, Natural History Museum of Los Angeles County. doi:10.15468/77rmwd (4,545 records)
• Oregon State University Herpetological Collection, Oregon State University. doi:10.15468/ckagzq (3,903 records)
• Georgia Southern University - Savannah Science Museum Herpetology Collection, Georgia Southern University. doi:10.15468/nruxuc (3,899 records)
• BugGuide - Identification, Images, & Information For Insects, Spiders & Their Kin For the United States & Canada, United States Geological Survey. doi:10.15468/sk2lxk (3,701 records)
• Reptile Specimens, Sam Noble Oklahoma Museum of Natural History. doi:10.15468/cplkwg (3,610 records)
• International Barcode of Life project (iBOL), The International Barcode of Life Consortium. doi:10.15468/inygc6 (3,434 records)

Ranges, identification and danger notes, checked against:

• The Reptile Database and the World Spider Catalog for names
• Savannah River Ecology Lab Herpetology, University of Georgia
• Florida Museum of Natural History, Florida snakes
• Texas Parks and Wildlife species pages
• Arizona reptiles and amphibians
• Missouri Department of Conservation field guide
• US Fish and Wildlife Service, eastern massasauga
• University of Kentucky Entomology, brown recluse and UC Riverside spider research
• UC IPM, spiders and UC IPM, scorpions
• Purdue Extension, spiders
• Poison Control and America's Poison Centers for the emergency numbers

Photos

Photos come from Wikimedia Commons and iNaturalist under licenses that allow reuse: public domain, CC0, CC BY and CC BY-SA. Each photo is credited where it appears. Illustrations on the home page and empty pages are made for this site and never stand in for a species.