Pennsylvania Hatch Chart: Complete Fly Fishing Guide by Month

Common Name	Latin Name	Hook Size	Start Date	Time
Little Black Stonefly	Allocapnia pygmaea	16	5-Mar	Late Morning & Afternoon
Little Blue Winged Olive Dun	Baetis spp. / B. tricaudatus	16–20	13-Mar	Late Morning & Afternoon
Midges	—	18–26	Mar (early)	All Day
Blue-Winged Olives (Spring)	Baetis vagans	18	1-Apr	Late Morning & Afternoon
Blue Quill	Paraleptophlebia adoptiva	16	5-Apr	Late Morning & Afternoon
Quill Gordon	Epeorus pleuralis	12–14	5-Apr	Afternoon
Grannom Caddis	Brachycentrus numerososus	12–14	9-Apr	Late Morning & Afternoon
Little Black Caddis	Chimarra aterrima	18	14-Apr	Mid Day
Black Quill	Leptophlebia cupida	14	12-Apr	Afternoon
Hendrickson (Female)	Ephemerella subvaria	12	12-Apr	Afternoon
Red Quill (Male)	Ephemerella subvaria	14	12-Apr	Afternoon
Dark Quill Gordon	Ameletus ludens	14	18-Apr	Afternoon
Blue-Winged Olive (late spring)	Baetis spp.	14–18	20-May	Mid Day
Cream Caddis	Psilotreta spp.	14–18	3-May	Morning & Afternoon
Green Caddis	Rhyacophila spp.	14	April (late)	Morning & Afternoon
March Brown	Stenonema vicarium	10–12	5-May	Late Morning & Afternoon
Little Blue Dun	Acentrella carolina	20	1-May	Afternoon & Evening
Sulphurs	Ephemerella dorothea	16–18	10-May	Evening
Sulphurs	Ephemerella invaria	14–16	10-May	Afternoon & Evening
Gray Fox	Stenonema vicarium	12	10-May	Late Morning & Afternoon
Light Cahill	Stenacron interpunctatum	12–14	20-May	Evening
Green Drake	Ephemera guttulata	8–10	20-May	Late Morning & Afternoon
Brown Drake	Ephemera simulans	10–14	25-May	Evening
Slate Drake	Isonychia bicolor / sadleri	12–14	26-May	Evening
Yellow Drake	Ephemera varia	10–12	June (late)	Evening
Trico	Tricorythodes stygiatus	20–24	5-Jul	Morning
White Fly	Ephoron leukon	10–12	7-Aug	Evening
Fall Slate Drake	Isonychia	12–14	September	Noon – Afternoons
Fall Little Blue Winged Olive	Baetis spp.	18–20	September	Mid Day
Fall Caddis	Pycnopsyche spp.	6–12	September (late)	Mid Day
October Caddis	Pycnopsyche guttifer / lepida	6–10	October	Afternoon & Evening
Micro Fall Caddis	Chimarra spp. / Hydroptila spp.	16–20	October–November	Afternoon & Evening

In Pennsylvania, fly hatches follow a seasonal rhythm—but no two years are exactly the same. Most aquatic insects begin to stir once stream temperatures settle into that ideal spring range: cool enough to remain clean and clear, yet warm enough to awaken both trout and insect life. A string of sunny afternoons can jumpstart an early Blue-Winged Olive (BWO) or Little Black Stonefly hatch, while a stretch of cold rain or high, murky water can delay everything just as quickly.

By May, when freestone streams drop and water temperatures inch into the low 50s, the bigger mayflies—March Browns, Gray Fox, Sulphurs, and eventually Green Drakes—start to emerge reliably. Spinner falls often wait for perfect evenings: calm air, fading light, and a quiet that feels like time itself has slowed down.

Spring-fed streams like Spring Creek or the Little Juniata operate on a steadier schedule, thanks to consistent groundwater temperatures. In contrast, freestone streams vary more widely, responding quickly to weather patterns and warming trends. Each year has its own quirks, but over time, anglers learn to read the season not just by the calendar, but by the water, weather, and light.

Hatch data compiled from the following sources: Charles Meck, Keystone Fly Fishing and its contributors, Al Caucci, Bob Nastasi, Rick Nyles, Dave Kile, and over 5,000 stream reports from Paflyfish (1997–2025).

 

This a great file to keep on hand! I always get questions at my TU meeting or new members at my tying club about what they should use at that time. I think I'll print this our to have on hand, especially for our Learn to Fly Fish Day! Thanks!

 

one fly that i saw coming off on the First Fork on the first week of OCT last fall , in the afternoon looked like a sz 18 sulfur, after catching one and doing some home work , i concluded it was a Leucrocuta hebe

 

pine and surrounding streams

 

Thank y'all for sharing this great info I'm adding it to my information I carry when and bf I fish here.

 

Thanks guys. Will help me catch up on creeks and streams back here. I wonder just how many people have actually seen this?