When people think about seed dispersal, birds and mammals usually come to mind first. They eat fruit, carry seeds away from parent plants and help forests regenerate across wide areas. A new scientific review suggests that an important part of this story has been overlooked much closer to the ground.
Researchers led by the University of Hong Kong found that small invertebrates — including slugs, earthworms, beetles, crickets and crab — can swallow seeds and later deposit them while the seeds are still capable of germinating.
The findings broaden the traditional understanding of how plants spread and may be especially relevant in fragmented forests where larger animal dispersers are becoming less common.
A Hidden Route for Seeds
The process is known as invertebrate endozoochory. It happens when seeds pass through an animal’s digestive system and remain viable afterwards.
The review combined evidence from 43 peer-reviewed studies and documented this type of seed dispersal in at least 51 invertebrate species involving 186 plant taxa across Asia, Europe, North America and Oceania.
That scale suggests the behaviour is not simply a collection of rare ecological curiosities. Instead, it may represent a widespread but under-recognised interaction between plants and small animals.
Professor Si-Chong Chen of the University of Hong Kong, who led the review, explained indirectly that researchers have historically underestimated invertebrates partly because of their small size. When their abundance and repeated interactions with plants are considered together, however, their cumulative ecological contribution may be substantial.
Crab Can Move Thousands of Seeds
Some examples are surprisingly dramatic.
The review describes freshwater crab in Japan that can consume more than a thousand tiny seeds in a single night before later depositing them inside underground burrows.
Those burrows may provide favourable conditions for germination because they remain humid and can protect seeds from drying out or being eaten by other animals.
Professor Kenji Suetsugu, a co-author of the research, noted that such behaviour shows how small animals can act as hidden gardeners on the forest floor, moving seeds into places where they may have a better chance of surviving.
Plants May Be Adapted to Small Dispersers
The researchers also identified a possible group of traits associated with plants that depend on these animals.
Such plants often produce very small, durable seeds inside inconspicuous fruits positioned close to the ground.
These fruits may attract less attention from birds and mammals, but they are readily accessible to slugs, beetles, crickets and other ground-dwelling species.
Passing through the digestive tract may also change the seed coat. In some cases, this process can improve germination by making it easier for water to enter the outer layer.
Short Distances Can Still Matter
Invertebrates generally do not move seeds as far as birds or large mammals.
But long-distance transport is not the only thing that matters.
Even moving a seed a short distance away from its parent plant can reduce competition for light, water and nutrients. It can also place the seed in a better microhabitat, such as moist soil, leaf litter or a sheltered burrow.
Chen’s team argues that this fine-scale movement may be particularly important because invertebrates are extremely abundant and constantly moving across the forest floor.
A Possible Safety Net for Forests
The findings may also have conservation implications.
Habitat fragmentation, hunting and other human pressures have reduced populations of many large birds and mammals that traditionally disperse seeds over long distances.
When those animals decline, plants that depend on them may struggle to colonise new areas or regenerate effectively.
Small invertebrates cannot completely replace larger dispersers, but they may provide an additional layer of resilience.
Chen suggested that their ability to place seeds into favourable small-scale environments could help maintain some level of plant regeneration even when larger animals become less common.
A Broader View of Forest Ecology
The review does not challenge the importance of birds and mammals. Instead, it adds another layer to the complex network of relationships that sustain forests.
Large animals remain essential for moving seeds across long distances, while small invertebrates may contribute through sheer numbers, frequent contact with fallen fruit and precise deposition close to the ground.
Researchers now want to know how common this process is across different ecosystems, how often seeds survive digestion and whether these interactions should be considered more explicitly in conservation and forest-restoration projects.
The main lesson is that some of the most important work in a forest may be happening almost invisibly underfoot. Tiny animals moving seeds only a few metres at a time can still influence where plants grow, how forests recover and how resilient ecosystems remain.
