What bit me in Pennsylvania?

19 biting or stinging species have verified records in Pennsylvania. The fastest way to narrow it down is where on your body the marks are and how they are arranged — below the knee in clusters points to fleas or chiggers, lines on uncovered skin point to bed bugs, scattered single bumps point to mosquitoes. Bite season here runs roughly April to October.

Active around now in Pennsylvania

• Honey bee
• Bald-faced hornet
• Carpenter ant
• American dog tick
• Paper wasp
• Deer tick
• Yellowjacket
• Black fly
• Horsefly
• Yellow sac spider

Recorded biting species in Pennsylvania

Record counts come from the GBIF biodiversity database and reflect how often a species is reported and identified in Pennsylvania. They are a guide to what is plausible here, not a census — and they say nothing about how likely you are to be bitten indoors.

Bite season month by month

Of the 19 species recorded in Pennsylvania, 19 are active in June — the peak of the local season. The humid continental climate here is what sets those boundaries: species that need warmth disappear at the edges of the year, while the indoor ones do not care.

Narrowing it down in three questions

1. Where on your body? Below the knee in clusters points to fleas or chiggers. Uncovered skin — arms, shoulders, neck — points to bed bugs or mosquitoes. Along a sock line or waistband is close to diagnostic for chiggers.
2. How are they arranged? A line or zigzag of three or more suggests bed bugs. Scattered single bumps suggest mosquitoes. A curved group with white pustules the next day means fire ants.
3. Indoors or outdoors, and when? Bites that appear overnight in one specific bed are a different problem from bites after an afternoon in tall grass. In Pennsylvania the outdoor season runs April to October; the indoor species run all year.

Stings rather than bites in Pennsylvania

Honey bee, Bald-faced hornet, Carpenter ant, Paper wasp, Yellowjacket are recorded here. Stings differ from bites in one way that matters: they can cause anaphylaxis in sensitised people, and that risk does not depend on how bad previous stings looked. Anyone who has had a severe reaction should carry an adrenaline auto-injector.

Species associated with illness here

• American dog tick bite — Rocky Mountain spotted fever, tularemia, tick paralysis (rare, resolves on removal)
• Deer tick bite — Lyme disease, anaplasmosis, babesiosis, Powassan virus (rare)
• Lone star tick bite — ehrlichiosis, Heartland virus, tularemia, STARI, alpha-gal syndrome (red meat allergy)
• Deer fly bite — tularemia (rare)
• Flea bite — murine typhus (Gulf Coast, California, Hawaii), cat scratch disease bacteria carried between cats, flea tapeworm (mainly in children who swallow a flea)

Most bites from these species transmit nothing. What matters is the follow-up: note the date of the bite, and report any fever or expanding rash in the following weeks to a clinician, mentioning the bite explicitly.

Year-round in Pennsylvania

Weather does not affect everything. Bed bugs, scabies and head lice depend on people rather than season, so a bite pattern in January in Pennsylvania points to those first — see what is biting me at night.