Venomous snakes and spiders in Iowa

Iowa's venomous snakes are three rattlesnake species. Together they account for 69 licensed records; the timber rattlesnake alone has 51% of them, and the least recorded, the eastern massasauga, has 14.

Also recorded in Iowa under any license, but fewer than 10 times and so not counted above: the western massasauga (8) and the eastern copperhead (3). Such records can be genuine rarities, strays or old misidentifications; see the rare list.

One recluse species (Brown recluse: 2 records) is on the Iowa list. Widow bites cause muscle pain and cramps; recluse bites can cause a slow-healing wound. Both are rare and seldom fatal.

These eight account for 72% of all licensed snake records in Iowa; the most recorded, the plains garter snake, alone for 20%.

These eight account for 45% of all licensed spider records in Iowa; the most recorded, the bold jumper, alone for 14%.

Observation records of snakes in Iowa run mostly April through October, peaking in May with 32% of them. December through February together hold under 2% of the records, so snakes in Iowa are rarely recorded in winter. Venomous snakes alone have five observation records with a month in Iowa, too few for a season of their own.

Observation records of spiders in Iowa run mostly May through October, peaking in September with 27% of them. December through February together hold under 2% of the records, so spiders in Iowa are rarely recorded in winter.

Madison County has the most records of venomous snakes in Iowa, 27, most of them of the timber rattlesnake. Lee County and Johnson County follow.

Woodbury County leads with 81 records (8%), followed by Madison County and Dickinson County; the top five counties hold 32% of the total. 93 of Iowa's 99 counties have at least one licensed snake record.

Yes. Iowa has three venomous snake species on its list, the kind people usually call poisonous: timber rattlesnake, prairie rattlesnake and eastern massasauga. Also recorded there, but too few times to list, counting records of any license: the western massasauga (8) and the eastern copperhead (3). Strictly, snakes are venomous (they inject venom), not poisonous (harmful to eat or touch).

Yes. Three species are on the Iowa list: the timber rattlesnake, the prairie rattlesnake and the eastern massasauga, with 69 licensed records between them. Most licensed records of the timber rattlesnake come from Madison County, Lee County and Johnson County. The western massasauga is recorded there too, but only eight times (records of any license), too few to list.

Not on the Iowa list: the eastern copperhead is recorded there only three times (records of any license), too few to list. Such records can be genuine rarities, strays, transported animals or misidentifications. Treat any snake that looks like a copperhead or cottonmouth as venomous.

No. GBIF holds no cottonmouth record for Iowa under any license.

No. GBIF holds no coral snake record for Iowa under any license.

Iowa has 35 licensed records of the timber rattlesnake, which ranks the state 19th of the 30 states where it reaches our threshold. Most of its licensed records in Iowa come from Madison County, Lee County and Johnson County. Range in other states and photos: Timber rattlesnake profile.

Iowa has 20 licensed records of the prairie rattlesnake, which ranks the state 13th of the 14 states where it reaches our threshold. Range in other states and photos: Prairie rattlesnake profile.

Iowa has 14 licensed records of the eastern massasauga, which ranks the state 7th of the 8 states where it reaches our threshold. Range in other states and photos: Eastern massasauga profile.

Many snakes and spiders taken for venomous ones are harmless species with a similar look. These are the usual confusions, with each species' licensed records in Iowa.

Copperheads are not on the Iowa list, but they are recorded in Iowa three times (records of any license: eastern copperhead 3): treat any snake like this as venomous until identified. Harmless species often taken for them in the state: northern water snake (104), eastern milksnake (29) and eastern hog-nosed snake (19).

No cottonmouths reach the Iowa list, and GBIF holds no cottonmouth record for Iowa under any license, so a snake taken for one here is most likely a harmless lookalike. Those recorded in the state: northern water snake (104).

Rattlesnakes: 69 licensed records in Iowa. Harmless species often taken for them are also on the state list: gopher snake (83), eastern fox snake (48), western foxsnake (40) and eastern hog-nosed snake (19). Together they have 190 licensed records, and the lookalikes are recorded 3 times as often.

No coral snakes reach the Iowa list, and GBIF holds no coral snake record for Iowa under any license, so a snake taken for one here is most likely a harmless lookalike. Those recorded in the state: eastern milksnake (29).

Widow spiders are not on the Iowa list, but they are recorded in Iowa seven times (records of any license: northern black widow 6, southern black widow 1): treat any spider like this as venomous until identified. Harmless species often taken for them in the state: triangulate bud spider (12) and boreal combfoot (2).

Recluse spiders: 2 licensed records in Iowa. Harmless species often taken for them are also on the state list: longbodied cellar spider (3). It has 3 licensed records, and the lookalikes are recorded 1.5 times as often.

By count of venomous snake species, Iowa ranks 20th of 50 states, level with 8 other states. Nationally, Arizona leads with 14 species; five list none.

Of the six states bordering Iowa, Missouri, Illinois and Nebraska list more venomous snake species (Iowa: 3 species; Missouri 5, Illinois 4, Nebraska 4, Wisconsin 2, Minnesota 1, South Dakota 1).

Venomous snakes listed next door but not in Iowa: the northern cottonmouth (Illinois and Missouri). Listed next door and recorded in Iowa too, but too few times to list (records of any license): the eastern copperhead, recorded here only three times (listed in Illinois, Missouri and Nebraska); the western massasauga, recorded here only eight times (listed in Missouri and Nebraska); the pygmy rattlesnake, recorded here only one time (listed in Missouri). The most widely shared is the timber rattlesnake, listed in five of the six bordering states.

Not on our list: GBIF holds 7 widow spider records of any license in Iowa (northern black widow 6, southern black widow 1), fewer than 10 of any one species; such records can be genuine rarities, strays, transported animals or misidentifications. Treat any spider that looks like a widow as venomous.

Yes. The brown recluse is on the Iowa list, with 2 licensed records.

Iowa has 2 licensed records of the brown recluse, which ranks the state 15th of the 16 states where it reaches our threshold. Range in other states and photos: Brown recluse profile.

No. GBIF holds no scorpion record for Iowa under any license. Every scorpion has venom; only the Arizona bark scorpion's sting is medically significant, and it is not on the Iowa list.