Introduced and assessed as invasive in the lower 48 states
iNaturalist's volunteer curators list it as introduced in their Ohio checklist.
US-RIIS assesses a species as invasive when it causes, or is likely to cause, harm there, or is at least locally abundant and harmful ecologically, economically, or to health.
Season shown in 1 of Ohio's 88 counties. Explore Ohio
No result yet (10)
Recorded, too few records for a result (62)
Recorded, season not shown (15)
Season shown (1)
Boundaries: U.S. Census Bureau, 2025 Cartographic Boundary Files, 1:500,000. Show as a table
Counties as a table
poison hemlock by Ohio county: records and mapped range
County
Records
Adams County
Recorded, too few records for a result
Allen County
Recorded, too few records for a result
Ashland County
21 · Recorded, season not shown
Ashtabula County
Recorded, too few records for a result
Athens County
122 · Season shown
Auglaize County
Recorded, too few records for a result
Belmont County
Recorded, too few records for a result
Brown County
Recorded, too few records for a result
Butler County
60 · Recorded, season not shown
Carroll County
Recorded, too few records for a result
Champaign County
Recorded, too few records for a result
Clark County
Recorded, too few records for a result
Clermont County
24 · Recorded, season not shown
Clinton County
Recorded, too few records for a result
Columbiana County
Recorded, too few records for a result
Coshocton County
Recorded, too few records for a result
Crawford County
Recorded, too few records for a result
Cuyahoga County
117 · Recorded, season not shown
Darke County
Recorded, too few records for a result
Defiance County
No qualifying records yet
Delaware County
Recorded, too few records for a result
Erie County
Recorded, too few records for a result
Fairfield County
Recorded, too few records for a result
Fayette County
Recorded, too few records for a result
Franklin County
116 · Recorded, season not shown
Fulton County
Recorded, too few records for a result
Gallia County
Recorded, too few records for a result
Geauga County
Recorded, too few records for a result
Greene County
55 · Recorded, season not shown
Guernsey County
Recorded, too few records for a result
Hamilton County
151 · Recorded, season not shown
Hancock County
Recorded, too few records for a result
Hardin County
Recorded, too few records for a result
Harrison County
No qualifying records yet
Henry County
No qualifying records yet
Highland County
Recorded, too few records for a result
Hocking County
Recorded, too few records for a result
Holmes County
Recorded, too few records for a result
Huron County
No qualifying records yet
Jackson County
Recorded, too few records for a result
Jefferson County
No qualifying records yet
Knox County
Recorded, too few records for a result
Lake County
Recorded, too few records for a result
Lawrence County
Recorded, too few records for a result
Licking County
38 · Recorded, season not shown
Logan County
Recorded, too few records for a result
Lorain County
Recorded, too few records for a result
Lucas County
45 · Recorded, season not shown
Madison County
Recorded, too few records for a result
Mahoning County
Recorded, too few records for a result
Marion County
Recorded, too few records for a result
Medina County
Recorded, too few records for a result
Meigs County
Recorded, too few records for a result
Mercer County
Recorded, too few records for a result
Miami County
Recorded, too few records for a result
Monroe County
No qualifying records yet
Montgomery County
38 · Recorded, season not shown
Morgan County
Recorded, too few records for a result
Morrow County
Recorded, too few records for a result
Muskingum County
Recorded, too few records for a result
Noble County
No qualifying records yet
Ottawa County
Recorded, too few records for a result
Paulding County
No qualifying records yet
Perry County
Recorded, too few records for a result
Pickaway County
Recorded, too few records for a result
Pike County
Recorded, too few records for a result
Portage County
Recorded, too few records for a result
Preble County
Recorded, too few records for a result
Putnam County
No qualifying records yet
Richland County
Recorded, too few records for a result
Ross County
20 · Recorded, season not shown
Sandusky County
Recorded, too few records for a result
Scioto County
Recorded, too few records for a result
Seneca County
Recorded, too few records for a result
Shelby County
Recorded, too few records for a result
Stark County
29 · Recorded, season not shown
Summit County
56 · Recorded, season not shown
Trumbull County
Recorded, too few records for a result
Tuscarawas County
Recorded, too few records for a result
Union County
Recorded, too few records for a result
Van Wert County
Recorded, too few records for a result
Vinton County
Recorded, too few records for a result
Warren County
37 · Recorded, season not shown
Washington County
Recorded, too few records for a result
Wayne County
22 · Recorded, season not shown
Williams County
Recorded, too few records for a result
Wood County
Recorded, too few records for a result
Wyandot County
No qualifying records yet
No mapped range from the range source used, the USGS Gap Analysis Project, which maps land vertebrates only.
Season
When it is recorded
In Warren County
Not enough evidence
The weeks are still too uncertain to show a season. Based on 37 records in 7 of the 10 years from 2016 to 2025, above the minimum of 20 records from 5 different years.
JanFebMarAprMayJunJulAugSepOctNovDec
Show over the bars
Recording in Warren County · records of all species each week, 16,872 in all
Records per week from 37 records in 7 of the 10 years from 2016 to 2025. Shows when people recorded it, not a season or how common it is.
Show as a table
Records of poison hemlock in Warren County each week, and records of all species
Week
Records of poison hemlock
Years recorded
Records of all species
Jan 4–10
0
0
108
Jan 11–17
0
0
29
Jan 18–24
0
0
28
Jan 25–31
0
0
37
Feb 1–7
0
0
23
Feb 8–14
1
1
38
Feb 15–21
0
0
66
Feb 22–28
0
0
65
Mar 1–7
0
0
53
Mar 8–14
0
0
70
Mar 15–21
0
0
116
Mar 22–28
1
1
117
Mar 29 – Apr 4
2
2
396
Apr 5–11
0
0
254
Apr 12–18
1
1
324
Apr 19–25
0
0
336
Apr 26 – May 2
4
2
539
May 3–9
3
2
323
May 10–16
2
2
423
May 17–23
4
3
420
May 24–30
4
4
378
May 31 – Jun 6
6
5
696
Jun 7–13
1
1
759
Jun 14–20
6
3
727
Jun 21–27
1
1
558
Jun 28 – Jul 4
0
0
552
Jul 5–11
0
0
695
Jul 12–18
0
0
643
Jul 19–25
0
0
564
Jul 26 – Aug 1
0
0
530
Aug 2–8
0
0
491
Aug 9–15
0
0
720
Aug 16–22
0
0
565
Aug 23–29
0
0
534
Aug 30 – Sep 5
0
0
719
Sep 6–12
0
0
619
Sep 13–19
0
0
584
Sep 20–26
0
0
390
Sep 27 – Oct 3
0
0
403
Oct 4–10
0
0
264
Oct 11–17
0
0
277
Oct 18–24
0
0
266
Oct 25–31
0
0
204
Nov 1–7
0
0
159
Nov 8–14
0
0
141
Nov 15–21
1
1
78
Nov 22–28
0
0
220
Nov 29 – Dec 5
0
0
53
Dec 6–12
0
0
58
Dec 13–19
0
0
45
Dec 20–26
0
0
75
Dec 27 – Jan 2
0
0
140
Reported in flower
Only 5 records here show flowers, too few to show a flowering season. One needs at least 20 records from 5 different years.
Reported in fruit
Only 1 records here show fruit, too few to show a fruiting season. One needs at least 20 records from 5 different years.
In Ohio
Not enough evidence
The weeks are still too uncertain to show a season. Based on 1,591 records in 10 of the 10 years from 2016 to 2025, above the minimum of 20 records from 5 different years.
This week · Nov 8–14
JanFebMarAprMayJunJulAugSepOctNovDec
Show over the bars
Recording in Ohio · records of all species each week, 1,691,199 in all
Records per week from 1,591 records in 10 of the 10 years from 2016 to 2025. Shows when people recorded it, not a season or how common it is.
Show as a table
Records of poison hemlock in Ohio each week, and records of all species
Week
Records of poison hemlock
Years recorded
Records of all species
Jan 4–10
4
3
6,211
Jan 11–17
6
4
5,146
Jan 18–24
5
4
4,645
Jan 25–31
4
4
4,698
Feb 1–7
3
2
6,023
Feb 8–14
9
4
5,888
Feb 15–21
11
2
5,436
Feb 22–28
10
5
6,846
Mar 1–7
15
6
8,321
Mar 8–14
13
6
10,384
Mar 15–21
27
6
12,620
Mar 22–28
41
7
13,949
Mar 29 – Apr 4
41
8
19,661
Apr 5–11
64
9
26,860
Apr 12–18
80
9
39,925
Apr 19–25
47
8
41,623
Apr 26 – May 2
96
9
56,391
May 3–9
78
10
52,952
May 10–16
115
8
53,785
May 17–23
123
10
57,698
May 24–30
128
10
54,651
May 31 – Jun 6
134
10
53,099
Jun 7–13
152
9
53,700
Jun 14–20
133
9
56,625
Jun 21–27
49
8
55,361
Jun 28 – Jul 4
35
9
58,477
Jul 5–11
21
8
61,336
Jul 12–18
15
8
64,722
Jul 19–25
8
6
69,753
Jul 26 – Aug 1
3
3
59,416
Aug 2–8
1
1
59,712
Aug 9–15
6
4
55,994
Aug 16–22
5
3
54,328
Aug 23–29
1
1
51,772
Aug 30 – Sep 5
6
4
57,167
Sep 6–12
2
2
59,075
Sep 13–19
5
3
54,543
Sep 20–26
4
2
45,860
Sep 27 – Oct 3
5
4
43,180
Oct 4–10
10
3
37,841
Oct 11–17
7
4
30,824
Oct 18–24
2
2
21,156
Oct 25–31
10
4
19,021
Nov 1–7
8
3
14,172
Nov 8–14
10
6
12,621
Nov 15–21
5
2
7,965
Nov 22–28
4
3
8,136
Nov 29 – Dec 5
3
3
6,083
Dec 6–12
6
4
6,004
Dec 13–19
5
4
5,423
Dec 20–26
4
3
5,661
Dec 27 – Jan 2
12
6
8,459
Reported in flower
No flowering season shown here. Most records come from a single year, so a season is not shown yet.
Reported in fruit
Only 12 records here show fruit, too few to show a fruiting season. One needs at least 20 records from 5 different years.
What these results show
These results show when people recorded a species, not when or where it occurs. Missing weeks and low counts do not mean absence or scarcity, and counts are not abundance. Contributed records reflect where, when and what people chose to observe.
Identification
How to identify it
Telling it apart
From what Ohio’s records show. Only what the records support is shown.
wild carrotDaucus carotaOften confused in Ohio: 26 identifications in Ohio named one where the other was meant
spreading chervilChaerophyllum procumbensOften confused in Ohio: 12 identifications in Ohio named one where the other was meant
common hedge parsleyTorilis arvensis212 identifications worldwide named one where the other was meant
water hemlockCicuta maculata109 identifications worldwide named one where the other was meant
From iNaturalist’s similar-species counts, refreshed monthly: confusions in Ohio first, then worldwide. Only species with an Ohio result are listed.
Land cover where it is recorded
Land cover
Its recordsAll Ohio records
Developed
60%49%
Forest
19%31%
Farmland
15%11%
Wetland
4%5%
Grassland and shrub
2%0.9%
Open water
0.4%3%
Barren
0.3%0.6%
From 1,068 records placed within 100 m, beside all Ohio records placed the same way. People record where they go, so this shows where records come from, not where the species lives. Land cover: USGS Annual NLCD, 2025 (opens in a new tab)
Sources
Where these results come from
Records from iNaturalist research-grade observations and expert-identified GBIF datasets, CC0, CC BY and CC BY-NC. Sources
Seasons use the published method and its evidence thresholds. Methods
A spreadsheet (CSV) with a link to each record, on iNaturalist or GBIF. Records whose location was hidden by the observer or the source are counted but not linked.
