What Happens to a Nut on the Forest Floor?

by Nicolette L. Cagle, June 1, 2026

What happens to a hickory nut or walnut after it falls to the forest floor? At first, it can seem like a simple thing, a stored future released from the canopy and left beneath the tree that made it. Imagine a hickory nut resting inside its husk, a black walnut darkening in the grass, or a pecan slipping into leaf litter.

But on the forest floor, a nut is part of a larger system of movement, shelter, and decay. It carries the tree’s future into a community of animals, insects, fungi, bacteria, and other soil organisms that will determine whether it is eaten, destroyed, or given the rare chance to germinate.

Walnuts (Juglans) and hickories, including pecans (Carya), are mast-producing trees. They create large, energy-rich seeds that appear in uneven pulses across years. In some years, a tree may produce relatively few nuts. In others, the ground beneath it may be covered. This variability shapes the lives of the animals that depend on them. In pignut hickory (Carya glabra), mast production, insect infestation, and the number of viable nuts varied strongly among years, suggesting that the availability of hickory nuts on the forest floor is shaped by both the tree’s reproductive rhythm and the many consumers waiting for that crop (Sork, 1983a).

The first part of a nut’s afterlife often belongs to vertebrates, including squirrels, chipmunks, mice, deer, and other animals that  recognize walnuts and hickories as concentrated food. These seeds are rich in stored energy, but they are also defended by husks, shells, and tannins. To eat a nut, an animal must work for it. To move a nut, an animal must decide whether the reward is worth the “weight”.

Those decisions shape the forest. Scatter-hoarding animals carry nuts away from the parent tree and bury them in soil, leaf litter, or other hidden places. Many cached nuts are later recovered and eaten, while others are stolen by different animals or forgotten. A forgotten cache is one of the ways a heavy seed becomes a new tree. Vander Wall (2001) described nut dispersal as part of a broad evolutionary relationship between large-seeded plants and scatter-hoarding animals. In black walnut, Stapanian and Smith (1978) framed this relationship through the coevolution of fox squirrels and walnuts, showing how the behavior of a squirrel and the traits of a nut can become intertwined.

Hickories participate in this same ecological exchange. Sork (1983b) found that mammalian seed dispersal of pignut hickory varied across fruiting seasons, with the fate of nuts depending on the shifting abundance of seeds and consumers. In a comparison of oak and hickory seed fate in a savanna-woodland system, hickory nuts were more likely to be cached and moved farther than acorns, while acorns were more often eaten near where they fell (Rusch et al., 2013/2016). These differences suggest that the physical character of the nut, its size, shell, and handling requirements, helps determine how it moves through the landscape.

Not every nut reaches the ground intact. Many are entered by insects while they are still developing on the tree. Curculios (long-snouted weevils) and other seed-feeding insects attack the young fruits and shoots of walnut and hickory, and older USDA work described these insects as important predators of developing nut crops (Brooks, 1922). In pignut hickory, insect infestation was one of the factors that shaped the number of viable nuts available in a given year (Sork, 1983a). In pecans, which are cultivated members of the genus Carya, insect damage can also change the microbial life of a nut. Wells (1976) isolated fungi such as Alternaria, Epicoccum, Penicillium, and other genera from weevil-damaged pecans, showing how an insect wound can become an opening for fungal colonization.

This is one of the most interesting parts of the story. An insect hole is an ecological doorway. Once the surface of a nut is pierced, moisture, spores, and other organisms can enter. A seed that has been breached participates differently in the forest-floor community. It may still feed an animal or it might decay into soil or become habitat.

After the kernel is eaten or decayed, the shell continues to have ecological value. Booher and colleagues (2017) studied cavity-dwelling ants in nuts on eastern U.S. forest floors and found that hollow nuts can serve as nest sites for a diverse ant community. Their work shows that an emptied nut can become a small chamber in the leaf litter, one of many tiny structures that support life close to the ground.

Fungi enter this story both early and late. A fungus may arrive through  insect openings, cracks, or prolonged contact with damp soil. They also enter through the broader work of decomposition. Fungi help soften the husk, break down organic compounds, and return stored nutrients to the soil. A nut’s richness makes it attractive both to animals and microbes.

The fungal communities of walnuts and pecans are best studied in agricultural and food-safety contexts, but those studies still help us understand what can happen when oily, nutrient-rich nuts interact with moisture, damage, and time. Tree nuts can host fungi from genera such as Penicillium, Aspergillus, Fusarium, Alternaria, and Cladosporium (Garcia et al., 2019; Tournas et al., 2015). In one survey of selected tree nuts and dried fruits, walnuts had especially high yeast and mold counts among the nuts examined, while pecans had lower counts in that sample set (Tournas et al., 2015). Walnut mold research also shows that fungal growth can begin through several pathways, including openings at the stylar or stem end of the nut, insect injury, husk damage, or nuts left on the ground under favorable conditions for mold development (Sacramento Valley Orchard Source, 2025).

In the forest, this fungal work is  part of the transformation of mast into soil. A walnut or hickory nut begins as a concentrated package of possibility. If it is not carried away, buried, or eaten, it gradually opens to the organisms around it, with its stored energy moving into animal bodies, microbial metabolism, and the soil.

This is the economy of the forest floor. A nut that fails to become a tree still contributes to the system that made it by feeding squirrel through winter, sheltering an ant colony, or nourishing the fungi that help return plant material to the soil. Its value is not limited to germination, but derives from a larger circulation of energy and relationship.

A Note for Pet Owners

Most fallen nuts are part of ordinary forest-floor ecology, but moldy nuts deserve caution around domestic animals, especially dogs.

The best-documented concern is tremorgenic mycotoxicosis in dogs after eating moldy walnuts. In dogs, clinical signs can include vomiting, tremors, ataxia, hypersensitivity to touch or sound, rapid heart rate, and seizures (Merck Veterinary Manual, 2024). The Merck Veterinary Manual describes walnuts and other moldy foods as possible substrates for Penicillium molds that can produce tremorgenic mycotoxins such as penitrems, roquefortine C, and related compounds. 

In a classic case report, penitrem A was found in moldy walnuts associated with dog intoxication, and Penicillium crustosum was isolated from those walnuts (Richard et al., 1981). A later case from New Zealand described a dog that developed neurologic signs after eating moldy walnuts, with tremorgenic mycotoxins detected in walnuts from the dog’s environment (Munday et al., 2008). A more recent retrospective study examined 54 dogs with mycotoxin intoxication after walnut ingestion, further supporting the veterinary significance of this risk (Braun et al., 2024).

The evidence is much stronger for moldy walnuts than for hickory nuts, but moldy hickory nuts and pecans should be treated with caution because moldy nuts can support fungi capable of producing mycotoxins. From personal experience, our dog has experienced tremors and other effects from eating hickory nuts, and I live with a veterinarian.

For people living with walnut and hickories, remember that these trees are valuable parts of the landscape, and their fallen nuts support a wide forest-floor community. At the same time, moldy walnuts and other moldy nuts should be removed from dog yards, kennels, and compost areas where pets have access. If a dog eats moldy nuts and develops shaking, vomiting, weakness, agitation, incoordination, or seizures, veterinary care is needed promptly.

Special thanks to Grant Cagle for sharing the literature on nut fungi and toxicity to dogs.

References

Booher, D. B., MacGown, J. A., Hubbell, S. P., & Duffield, R. M. (2017). Density and dispersion of cavity dwelling ant species in nuts of eastern US forest floors. Transactions of the American Entomological Society, 143, 79–93. https://doi.org/10.3157/061.143.0105

Braun, V., Kanstinger, A., et al. (2024). Mykotoxinvergiftung nach Walnussaufnahme bei 54 Hunden [Mycotoxin intoxication in 54 dogs after ingestion of walnuts]. Tierärztliche Praxis Ausgabe K: Kleintiere/Heimtiere, 52(4), 211–219. https://doi.org/10.1055/a-2344-6146

Brooks, F. E. (1922). Curculios that attack the young fruits and shoots of walnut and hickory (U.S. Department of Agriculture Bulletin No. 1066). U.S. Department of Agriculture.

Garcia, M. V., et al. (2019). Mycological quality of pecan nuts from Brazil: Absence of aflatoxigenic fungi and aflatoxins. Ciência Rural, 49(5), e20180742.

Merck Veterinary Manual. (2024). Tremorgenic neuromycotoxicosis in dogs. Merck & Co.

Munday, J. S., Thompson, D., Finch, S. C., Babu, J. V., Wilkins, A. L., di Menna, M. E., & Miles, C. O. (2008). Presumptive tremorgenic mycotoxicosis in a dog in New Zealand, after eating mouldy walnuts. New Zealand Veterinary Journal, 56(3), 145–148. https://doi.org/10.1080/00480169.2008.36823

Richard, J. L., Bacchetti, P., & Arp, L. H. (1981). Moldy walnut toxicosis in a dog, caused by the mycotoxin, penitrem A. Mycopathologia, 76, 55–58. https://doi.org/10.1007/BF00761899

Rusch, D. B., Midgley, J. J., & Anderson, R. C. (2013/2016). A comparison of seed predation, seed dispersal, and seedling herbivory in oak and hickory species with contrasting regenerating abilities in a bluegrass savanna-woodland habitat. Castanea.

Sacramento Valley Orchard Source. (2025). Walnut mold and how to manage it. University of California Agriculture and Natural Resources.

Sork, V. L. (1983a). Mast-fruiting in hickories and availability of nuts. American Midland Naturalist, 109, 81–88. https://doi.org/10.2307/2425518

Sork, V. L. (1983b). Mammalian seed dispersal of pignut hickory during three fruiting seasons. Ecology, 64, 1049–1056.

Stapanian, M. A., & Smith, C. C. (1978). A model for seed scatterhoarding: Coevolution of fox squirrels and black walnuts. Ecology, 59(5), 884–896. https://doi.org/10.2307/1938541

Tournas, V. H., Niazi, N. S., & Kohn, J. S. (2015). Fungal presence in selected tree nuts and dried fruits. Microbiology Insights, 8, 1–6. https://doi.org/10.4137/MBI.S24308

Vander Wall, S. B. (2001). The evolutionary ecology of nut dispersal. The Botanical Review, 67(1), 74–117.

Wells, J. M. (1976). Toxigenic species of Penicillium, Fusarium, and Aspergillus isolated from weevil-damaged pecans. Applied and Environmental Microbiology, 32(2), 324–327.