Tumbling Puffball
Bovista pila
Also called tumbling bovist, ball bovist, bronze puffball
A smooth round puffball that sheds its white outer skin to reveal a bronze to purplish-grey shell, hanging from a single tough cord until it breaks free and rolls. Common in open woods and pasture across North America.
Overview
The Tumbling Puffball is the largest of the widespread North American Bovista species, producing smooth, almost perfectly spherical fruiting bodies 3-8 cm across in pastures, lawns and open woodland. It is best known for the way it matures: the white outer skin sloughs off to leave a metallic bronze to purplish-grey inner ball which hangs from a single tough cord until wind and weather tear it loose.
Like other members of the genus it lacks a stalk and lacks any substantial sterile base, so the whole interior converts to spore powder held in a branched capillitium. This makes the mature fruiting body remarkably light for its size, an obvious advantage for a fungus that disperses by rolling.
Its smooth surface distinguishes it immediately from the spiny and warty Lycoperdon puffballs that often share the same ground.
How to identify it
Fruiting body
Globose, 3-8 cm across, smooth and even in outline, sometimes very slightly flattened at the base. Young specimens are white to pale tan and smooth or minutely felted, without spines or coarse warts.
Skin layers
The thin white to buff outer layer weathers and peels away, often in large patches, exposing a tough, papery to leathery inner skin of bronze, coppery-grey or purplish-bronze that develops a metallic sheen as it dries.
Attachment and stipe
No stalk and only a rudimentary sterile base. The ball is attached at a single point by a stout, tough cord of mycelium; unlike the flimsy threads of Bovista plumbea, this cord holds the fruiting body in place for some time before finally parting.
Flesh and spore mass
White, firm and homogeneous when young, then yellowish, olive and finally a dry olive-brown to dark brown powder. An irregular apical tear opens at maturity. Spores in mass are olive-brown to dark brown, and microscopically they bear the long pedicels characteristic of the genus.
Where and when it grows
Grows on soil in a wide range of open habitats: pastures, meadows, lawns, parkland, grassy roadsides, and open deciduous or mixed woodland with a sparse ground layer. It is scattered to gregarious and sometimes forms arcs or rings.
Widespread and common across much of North America, from the eastern deciduous forests through the Midwest and into the West, and reported from other temperate regions. Fruiting runs from summer through autumn, with old bronze shells persisting long after.
Ecological role
Bovista pila is saprotrophic. Its mycelium decomposes soil organic matter, buried leaf and grass litter and fine root debris, and it recycles nutrients through the upper soil profile of grassland and open woodland alike.
Once the interior has dried into powder, the fruiting body's rigid but hollow shell becomes a wind-driven disperser. The tough basal cord eventually snaps, the ball rolls, and each impact drives spore clouds out through the apical opening. Empty shells are frequently found far downwind or lodged against fences and hedgerows.
Similar species
Bovista plumbea is much smaller (2-3 cm), lead-grey rather than bronze beneath the outer skin, and attached by a tuft of fine threads instead of a single stout cord. Bovista nigrescens is intermediate in size and has a shining purple-black inner skin. Calvatia craniiformis is larger and skull-shaped with a wrinkled surface and a big, persistent, spongy sterile base that stays behind as a cup on the ground.
Lycoperdon species such as L. perlatum and L. marginatum are pear-shaped with an obvious stalk-like sterile base and carry spines or warts; L. marginatum peels its outer layer away in sheets but retains that sterile base, which Bovista pila never has.