Best Time to See Jellyfishes in Delaware
July, August and September is the best time to see jellyfishes in Delaware. Based on 568 verified iNaturalist observations, here is exactly when jellyfishes are most active across the year in Delaware.
By Tim, founder of Easy Street Markets. I maintain the wildlife database and verify every animal and source myself. Updated June 28, 2026.
Bay Nettle · inbetweenbays CC BY
Bay Nettle · inbetweenbays CC BY
Moon Jellies · inbetweenbays CC BY
568 verified observations of jellyfishes in Delaware, recorded across 12 months of the year on iNaturalist.
When jellyfishes are recorded in Delaware
Peak month
July
188 records (33.1% of the year)
| Month | Observations | Share |
|---|---|---|
| January | 7 | 1.2% |
| February | 6 | 1.1% |
| March | 5 | 0.9% |
| April | 11 | 1.9% |
| May | 3 | 0.5% |
| June | 40 | 7% |
| Julypeak | 188 | 33.1% |
| Augustpeak | 154 | 27.1% |
| Septemberpeak | 55 | 9.7% |
| October | 42 | 7.4% |
| November | 34 | 6% |
| December | 23 | 4% |
Jellyfishes you are most likely to see
| Species | Verified observations |
|---|---|
| Bay Nettle | 104 |
| Dwarf Lion's Mane Jelly | 78 |
| Mushroom Jelly | 45 |
| Common Moon Jelly | 32 |
| Southern Moon Jelly | 31 |
| Cannonball Jelly | 23 |
| Atlantic Sea Nettle | 22 |
| Atlantic Lion's Mane Jelly | 5 |
Weather to expect, source Open-Meteo
Typical weather in Delaware
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 65 to 86 degrees Fahrenheit, so pack for that.
| Month | Avg high | Avg low | Rain |
|---|---|---|---|
| Jan | 44°F | 32°F | 2.9" |
| Feb | 47°F | 33°F | 3.8" |
| Mar | 54°F | 39°F | 3.8" |
| Apr | 63°F | 48°F | 4.5" |
| May | 70°F | 56°F | 3.9" |
| Jun | 79°F | 66°F | 3.9" |
| Julbest time | 86°F | 73°F | 6" |
| Augbest time | 83°F | 72°F | 5.1" |
| Sepbest time | 77°F | 65°F | 4.3" |
| Oct | 68°F | 55°F | 4.4" |
| Nov | 56°F | 43°F | 2.8" |
| Dec | 48°F | 36°F | 4.8" |
Typical recent conditions (5-year means) from the Open-Meteo archive, averaged for Delaware. Weather varies year to year, so treat these as a guide.
Sightings of jellyfishes in Delaware peak in July, when 188 of the year's 568 verified observations are logged — about 33.1% of the annual total. Activity stays high through July, August and September.
The quietest stretch is May, when jellyfishes are hardest to find — May 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 Delaware are Bay Nettle, Dwarf Lion's Mane Jelly and Mushroom Jelly — 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 Delaware
- Captain John Smith Chesapeake National Historic Trail — National Historic Trail
- Chesapeake Bay
- First State National Historical Park — National Historical Park
- Washington-Rochambeau Revolutionary Route National Historic Trail — National Historic Trail
Frequently asked questions
What is the best month to see jellyfishes in Delaware?+
July is the single best month, and the broader peak window runs through July, August and September, based on 568 verified iNaturalist observations.
When are jellyfishes hardest to see in Delaware?+
May is the quietest month for jellyfishes in Delaware, with only 3 verified records.
Are jellyfishes active year-round in Delaware?+
Jellyfishes are recorded in 12 of 12 months in Delaware, so they can be seen year-round, with a clear peak in July.
More places to see jellyfishes
More wildlife in Delaware