Photinus pyralis

The Big Dipper Firefly
Photinus pyralis


The Big Dipper Photinus pyralis on Queen Anne's Lace. July 08, 2014, Wheatley, Ontario.
The Big Dipper Photinus pyralis on Queen Anne’s Lace. July 08, 2014, Wheatley, Ontario.

Head: Black, mouth dull reddish. Male has large eyes than female.
Antenna: Black, segments (11) slightly flattened. Tips of segments with faint white. Segment 2 very short.
Thorax (Pronotum): Somewhat triangular to semi-circular with front tip (base) squared. Black center spot, almost round with flattened front, widely surrounded on three sides by rose (reddish-orange) and at front (base) by yellow. Main ID: Black round spot does not extend to any border or edge.  Rest of pronotum yellowish, the yellowish somewhat translucent and may be slightly rose on front half (base). Underside mostly rose with some white.

Wings (Elytra): Oblong, blackish-brown, with uniform width golden margins. Center base of wings (scutellum) triangular, golden.
Legs: Thighs (femora) yellowish-brown, tips dark. Rest of legs brown.
Abdomen: Black on top side, lower margin of segments with yellowish-white line, more so on male. Underside of male segments 1 to 4 brown, side edges white. Segments 5 and 6 yellowish-white – flashes J-shaped yellow.
Underside of  female segments 1 to 4 brown; each segment has yellowish-white line on lower margin. Segment 5 yellowish-white (light organ), base sometimes has dark streaks. Segment 6 and tip golden brown.

Similar Species: Some of the darker Photinus marginellus may appear as faded P. pyralis, but the black spot at center is never as large or dark on P. marginellus.

Size: 10 to 14 mm.

Habitat: Meadows to urban gardens, parks and woods.

Food: Adults found on Queen Anne’s Lace and Trumpet Vine.

The Big Dipper Photinus pyralis male feed on Trumpet Vine flower. July 09, 2013, Wheatley, Ontario.
The Big Dipper Photinus pyralis male feed on Trumpet Vine flower. July 09, 2013, Wheatley, Ontario.

Flight Time: Early July to early August.

Life Cycle: Males emit long, distinctive J-shaped flash at dusk. Females respond with a flash, then mating takes place. Females lay eggs on or in the ground. Larvae live underground and feed on earthworms and other smaller insects. Adults tolerate light pollution, and come to lights at night; during the day they stay exposed on flowers, and man-made structures. Adults use

‘reflex bleeding’, oozing fluid when disturbed or threatened. These defensive poisons attract the female Pennsylvanica Firefly Photuris pennsylvanica. She needs these chemicals for egg development and preys upon the Big Dipper males by copying flashes of their females. When the male lands, the  Pennsylvanica female consumes the Big Dipper male and the chemicals.

Comments: Essex County – Ojibway Prairies 2005 and 2008 list of insects. Luk reported Photinus pyralis as new to Ojibway in 2010. Wheatley, 2013 and 2014 per photos.

For information on synonyms, references and type specimens see next page