Best Time to See Jellyfishes in Massachusetts
June, May and August is the best time to see jellyfishes in Massachusetts. Based on 1,950 verified iNaturalist observations, here is exactly when jellyfishes are most active across the year in Massachusetts.
By Tim, founder of Easy Street Markets. I maintain the wildlife database and verify every animal and source myself. Updated June 28, 2026.
Mauve Stinger · Thomas Irvine CC BY
Atlantic Lion's Mane Jelly · Morg CC BY
Lion's Mane Jellies · Ali Campbell CC BY
1,950 verified observations of jellyfishes in Massachusetts, recorded across 12 months of the year on iNaturalist.
When jellyfishes are recorded in Massachusetts
Peak month
June
471 records (24.2% of the year)
| Month | Observations | Share |
|---|---|---|
| January | 4 | 0.2% |
| February | 6 | 0.3% |
| March | 52 | 2.7% |
| April | 227 | 11.6% |
| Maypeak | 419 | 21.5% |
| Junepeak | 471 | 24.2% |
| July | 207 | 10.6% |
| Augustpeak | 295 | 15.1% |
| September | 178 | 9.1% |
| October | 83 | 4.3% |
| November | 5 | 0.3% |
| December | 3 | 0.2% |
Jellyfishes you are most likely to see
| Species | Verified observations |
|---|---|
| Atlantic Lion's Mane Jelly | 610 |
| Common Moon Jelly | 174 |
| Bay Nettle | 169 |
| Atlantic Sea Nettle | 45 |
| Dwarf Lion's Mane Jelly | 32 |
| Mauve Stinger | 31 |
| Lion's Mane Jelly | 10 |
| Southern Moon Jelly | 8 |
Weather to expect, source Open-Meteo
Typical weather in Massachusetts
Recent typical conditions by month, so you can plan a trip around both when jellyfishes are active and what the weather is doing. The best months to look for jellyfishes sit around 47 to 82 degrees Fahrenheit, so pack for that.
| Month | Avg high | Avg low | Rain |
|---|---|---|---|
| Jan | 37°F | 22°F | 3.8" |
| Feb | 39°F | 22°F | 3.4" |
| Mar | 48°F | 28°F | 3.6" |
| Apr | 57°F | 38°F | 4.6" |
| Maybest time | 68°F | 47°F | 3.4" |
| Junbest time | 78°F | 58°F | 3.6" |
| Jul | 83°F | 65°F | 5.4" |
| Augbest time | 82°F | 64°F | 3.5" |
| Sep | 73°F | 56°F | 5.3" |
| Oct | 62°F | 47°F | 5.3" |
| Nov | 50°F | 34°F | 3.1" |
| Dec | 42°F | 27°F | 5.9" |
Typical recent conditions (5-year means) from the Open-Meteo archive, averaged for Massachusetts. Weather varies year to year, so treat these as a guide.
Sightings of jellyfishes in Massachusetts peak in June, when 471 of the year's 1,950 verified observations are logged — about 24.2% of the annual total. Activity stays high through June, May and August.
The quietest stretch is December and January, when jellyfishes are hardest to find — December sees just 3 records. If a reliable sighting matters, plan around the peak window rather than the off-season.
The jellyfishes you are most likely to encounter in Massachusetts are Atlantic Lion's Mane Jelly, Common Moon Jelly and Bay Nettle — the most-recorded species in the state. Each keeps its own seasonal rhythm, but the month-by-month pattern above reflects every reported sighting together.
Where to go
Best places to see jellyfishes in Massachusetts
- Appalachian National Scenic Trail — National Scenic Trail
- Blackstone River Valley National Historical Park — National Historical Park
- Boston Harbor Islands National Recreation Area — National Recreation Area
- Cape Cod National Seashore — National Seashore
- Adams National Historical Park — National Historical Park
- Boston African American National Historic Site — National Historic Site
Frequently asked questions
What is the best month to see jellyfishes in Massachusetts?+
June is the single best month, and the broader peak window runs through June, May and August, based on 1,950 verified iNaturalist observations.
When are jellyfishes hardest to see in Massachusetts?+
December is the quietest month for jellyfishes in Massachusetts, with only 3 verified records.
Are jellyfishes active year-round in Massachusetts?+
Jellyfishes are recorded in 12 of 12 months in Massachusetts, so they can be seen year-round, with a clear peak in June.
More places to see jellyfishes
More wildlife in Massachusetts