Winter fireflies: the firefly that spends winter on tree bark

Why this time of year

In a Massachusetts study the adults showed up on their trees in fall and the count held steady from November through March. None flew from late September until March, and from early March they walked more on the bark. Pairs mated on the trunks from early April to mid-May.

How to notice it

1. On a dry day, walk a woodland and scan the deep grooves of rough-barked trunks from the ground up to about head height. The Massachusetts study searched trunks up to 2 m.
2. If one tree has them, check its neighbors too. In that study the beetles crowded onto three oaks, and the trees next to them had few or none.
3. Come back on warm days in March and April. From early March they move more along the bark, and from early April you may see mating pairs on the trunk.
4. In the Massachusetts study, some turned up in early April near sap oozing from sugar maples, and sugar makers know them as sap bucket beetles. Look only: do not pry bark or pick beetles off the tree.

Sources

• journals.flvc.orgPRIMARY, peer-reviewed. Rooney and Lewis 2000, Florida Entomologist 83(3):324-334; I downloaded and read the full PDF. The study was done in eastern Massachusetts: a mixed pine and deciduous forest at a Mass Audubon sanctuary, plus two other sites nearby. Adults are diurnal and 'lack adult light organs'. The genus is 'closely related to nocturnal beetles in the genus Photinus'. Beetles were marked from their 'fall appearance (October 1997) to spring dispersal (April 1998)'. 'the E. corrusca population remained fairly constant through the winter (November through March)'. This puts adults on trunks in December. 'number of adults on trees declined dramatically beginning in April and continuing through May'. From 28 September to 7 March adults never flew. By 18 March they flew back to the tree. 'Starting in early March, adults also showed increased movement along the bark surface.' 'Mating pairs were observed on trees from early April to mid-May'. The first field pair was seen on 7 April and the last field copulation on 21 May. Mating 'took place primarily on tree trunks'. The beetles occupied 'grooves in the bark of three Eastern black oaks'. On adjacent trees 'there were few or no beetles'. Trees were searched from the ground up to 2 m. Adults were 'found in early April near sap flows on Acer saccharum (sugar maple) trees' and are 'commonly found drowned in sap-collecting buckets'. Size in that population: 6 to 13 mm elytral length; the pictured beetle is 1.3 cm. Monthly overwinter survival was 88% to 99% (Massachusetts, 1997-98). Adults were absent from the trees June through July 1998 and gathered again the following August. 'in New England E. corrusca spends approximately 10 months as adults (August through May)'. Adults 'mate in early spring on their overwintering trees'.
• extension.umaine.eduPrimary, state extension (University of Maine Cooperative Extension). Adults 'overwinter at the base of trees, or in the cracks of tree bark or underneath loose bark'. They are 'one of the first insects to appear each spring, becoming active as early as late February'; the page is written for Maine. 'The bulk of their mating, however, takes place in April and May'. Maple syrup producers 'find them floating in their sap buckets in the spring', and 'another common name for these firefly beetles is in fact the Sap Bucket Beetle.' They 'gather around the freeze cracks and other wounds found on trees.' The species 'is probably in actuality a complex of several different species'. Gives no size or markings.
• northernwoodlands.orgSecondary (Northern Woodlands 'Outside Story' column by Laurie D. Morrissey, a New Hampshire writer). Use it for identification only: adults are 'dark brown or black - about a half inch in length' with curved orange, parenthesis-shaped marks on the shield over the head. They overwinter as adults on bark, are 'active as early as late February', mate 'in the grooves of tree bark from early April through mid-May', and turn up 'floating on the surface of the sap'; also called sap bucket beetles. Adults have no light organs.
• eaglehill.usPrimary, peer-reviewed (Deyrup et al. 2017, Northeastern Naturalist 24, Special Issue 7). Citing Rooney and Lewis 2000: 'In northeastern Massachusetts, Winter Firefly adults appear from late-summer through autumn on tree bark' and 'remain exposed in this microhabitat throughout the winter.' Adults 'mate diurnally in the early spring', 'adults lack a light organ', and winter mortality is minimal. For comparison, in eastern Tennessee adults are on trunks October to February. That is not used for the Massachusetts months.
• api.gbif.orgTaxonomic database (GBIF backbone, record last interpreted 2023-08-22). It lists Ellychnia corrusca with taxonomicStatus 'SYNONYM' and accepted name 'Photinus corrusca (Linnaeus, 1767)', vernacular name 'Winter Firefly'. Use it only to support keeping Latin names out of reader text.

Checked against these sources on November 6, 2026.

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