Moths are the secret pollinators. They fly at dusk or after dark, tend to be small, and have blotchy color patterns. For all those reasons, they get little attention. And yet: Moths are very numerous. They make up most of the insect order Lepidoptera, moths and butterflies. Lepidoptera are the second largest group of insects, after beetles, with 180,000 species, which is about 10% of all described living organisms. Lepidoptera are broken into 126 families; two families are butterflies, 17, 000 species, the rest are moths. So nearly 10% of the world's organisms are moths. And yet we generally overlook them.
 |
| big tropical moth, about an inch across |
Moths look a lot like butterflies, but usually moths are drably colored. Nevertheless, some moth species are very showy link. Most moths have feathery antennae, which distinguish them from butterflies which mainly have club-like antennae. The two groups share the life cycle of eggs that develop into larvae (caterpillars) that eat plants (and sometimes other things), then undergo complete metamorphosis into the flying moth/butterfly that mates and lays the eggs that start the cycle over again.
Adult moths may not feed at all, but many of those that do visit flowers for nectar and in so doing, pollinate. Other moth species visit flowers to lay eggs so their larvae can eat the developing seeds, but are brushed with pollen and pollinate as they visit the flowers.
While there are numerous exceptions, most moths fly at night. That is part of why people are unaware of them. By day, many of these moths hide on trees or in the leaf litter, camouflaged by their gray or brown coloring.
Reading about moth pollination, I learned that remarkably little is actually known. I can find reports of pollinating species in nine families, moths in the families Noctuidae, Sphingidae, Geometridae, Crambidae, Hepialidae, Zygaenidae, Pterophoridae, Gracillariidae, and Prodoxidae. Probably additional small moths have not been identified. Which doesn't seem very many out of 124 families of moths.
They can be abundant pollinators, though. Capturing moths at lights and looking for pollen on them in England Walton and collaborators found 381 of 838 (45%) of moths collected over two summers were carrying pollen. They represented 103 moth species. In Oliveira et al.'s study in the Cerrados of Brazil, 8 of the 38 (21%) of the most common woody species were moth-pollinated.
Many of the famous cases of moth pollination are by hawkmoths, also called sphinx moths and hummingbird moths (family Sphingidae). Hawkmoths are relatively big moths that fly in the twilight, they hover when visiting flowers, their wings moving fast so they look like tiny hummingbirds.
 |
| hawkmoth, probably hummingbird clearwing Hemaris thysbe |
Moths of other families that pollinate are collectively called "settling moths" because they land on the flower and stand there probing for nectar. This is the group that everyone agrees is poorly understood, although it includes the very famous yucca-yucca moth obligate mutualism (see below).
 |
| a settling moth, the bindweed moth (Tyta luctuosa), on a bachelor button (Centaurea cyanus) |
Moth pollination is very hard to study. They fly in the night when humans cannot see very well. A recent paper (Walton et al. see references) made that clear: they contrasted butterfly and moth pollination in the same fields. For butterflies they filmed the fields and analyzed the photos. For moths they attracted moths to lights and looked for pollen on the moths, a much more laborious and indirect approach.
Lots of plants have flowers that remain open all night. It is easy to see bees and butterflies on a cone flower (Echinacea) or sunflower (Helianthus), but perhaps, in addition, moths pollinate these flowers at night. They certainly could.
Some moths do fly by day or in twilight, those moths are regularly observed (my photos, for example). When it is really dark, seeing and following pollinators is much harder. You can rarely see where the insect goes next, and if you add lights, it disrupts all moth activity, to mention two obvious problems.
 |
| big jasmine in full bloom |
Some plants are predominantly moth-pollinated. These have share characteristics that facilitate visits by moths. 1) they tend to have white or pale-colored flowers, the easiest colors to see at night. White species of jasmine (Jasminum) are good examples. 2) they have to be open at night; for moth specialist plants that means opening new flowers, full of nectar and fresh pollen, at or after dark. 3) Many release a strong scent to attract pollinators, in twilight or after dark, for example, jasmines. 4) The flowers are often narrow tubes; the moth reaches in with its proboscis and gets pollen on itself while it is probing for nectar. 5) The flowers may close by day, as is the case for white evening primroses (Oenothera), but many moth-pollinated flowers last, staying open or reopening, several days to a week, apparently because nightly moth activity varies a lot. 6) The flowers tend to be above the foliage, easy for moths to reach.
 |
| Plumeria, frangipani, pollinated by large tropical hawknoths (Sphingidae) flowers are held above the foliage. |
I'll write separate posts about pollination by hawkmoths and settling moths. The flowers of hawkmoths are bigger than those of settling moths as a rule. The biggest moth in the world is 10" across (Hercules moth Cosinocera hercules of New Guinea and Australia), but most moths are less than an inch long, so moths are effective pollinators of medium sized to small flowers. Really big white tropical flowers with a strong scent, such as angel's trumpet (Brugmansia), are generally pollinated by bats.
One of the best-known moth-pollinated plants, yucca, has obligate mutualistic relationship with the moths. Mutualism is a relationship between organisms that benefits both, usually contrasted with predation and competition. Pollination is generally a mutualism, the animals get food, the plant gets pollen moved between flowers. Most pollination is pretty generalized: multiple animal species visit the flowers and carry out pollination; multiple flower species share the same animal pollinators. Obligate relationships are rare; biologists think they go extinct more easily than more general mutualisms. In an obligate pollination mutualism, the pollinator can only feed from one (or a few closely related) plants and the plant is only pollinated by one (or a few related) animals.
 |
| Yucca glauca There is no nectar. The pollen doesn't fall from the anthers; the yucca moth has to gather and transfer it. |
The very famous obligate mutualism between the yucca moths (Teticula and Parateticula, family Prodoxidae) and yucca (genus Yucca, 40-50 species in the plant family Agavaceae, relatively common plants of southwestern North America) has been studied for than 150 years. Yucca moths pollinate yucca flowers and lay their eggs in the flowers. Yucca moth caterpillars eat developing yucca seeds, their only food. Conversely, the yucca plant is dependent on yucca moths for pollination. The pollen does not come off or brush off, the yucca moth female gathers it, flies to another flower, and deposits it on the stigma before laying her eggs. Plant and insect have to have each other or they perish. Yucca seeds form in a vertical column as the fruit develops; generally the moth larvae leave a column of seeds untouched. (Most years the female moths are careful not to put too many eggs into a single flower.) It seems a strange system but both partners are doing well.
Many moths lay their eggs in flowers and the larvae devour the plant's seeds; in some cases that has evolved into an obligate mutualism. The yucca-yucca moth mutualism undoubtedly evolved from the moth larvae eating yucca seeds. A similar obligate mutualism exists between senita moths (Upiga virescens) and the white, night-flowering senita cactus, Lophocereus schottii, also in North America's southwest. The moths carry pollen between the flowers and lay their eggs to devour some but not all of the seeds. Kato and colleagues in Japan recently reported a settling moth obligate mutualism in a large group of tropical plants in the plant family Phyllanthaceae, finding that obligate pollination mutualism evolved at least five separate times. Their work suggests that more obligate pollination mutualisms exist. The current list is five distinct systems of obligate pollination mutualism: yuccas, figs and fig-wasps, senita cactus, plants in the Phyllantheae with Epicephala moths (Gracillariidae), thrips with cycads in Australia), the latter two discovered since 2000. It further suggests that more moth-pollinated plants exist than have been studied, since, of all the world's pollination systems, thousands of species interacting, only five obligate pollination mutualisms are known but three involve settling moths. Surely many more general moth pollination systems wait to be documented.
 |
| tropical moth |
Moths are the unknown pollinators, believed to be important but from only limited information. Certainly there are many plants with white tubular flowers that evolved to attract moth pollinators. But the moths in my photos, above, are visiting a blue-flowered bachelor button and a pink vervain, not typical moth flowers, so potentially moths pollinate many more plants that just those with white tubular flowers. Keep an eye out for moths that might be pollinators and for new reports of pollination by moths as they appear.
Comments and corrections welcome.
References
Althoff, D. M. 2016. Specialization in the yucca–yucca moth obligate pollination mutualism: A role for antagonism? American Journal of Botany. 103 (10): 1803-1809 link One of many many papers on the yucca-yucca moth mutualism, relatively recent with a review and lots of details I did not include. Accessed 2/10/25.
Fallln, C. 2021. For the Love of Moths. Xerces Society for-love-of-moths Accessed 2/6/25.
Fleming, T. H. and J. N. Holland. 1998. The evolution of obligate pollination mutualisms: senita cactus and senita moth. Oecologia. 114: 368-375.
Hahn, M. and C. A. Brühl. 2016. The secret pollinators: an overview of moth pollination with a focus on Europe and North America. Arthropod-Plant Interactions. 10:21-28.
Kawakita, A. and M. Kato. 2009. Repeated independent evolution of obligate pollination mutualism in the Phyllantheae-Epicephala association. Proceedings of the Royal Society. B. 276: 417-426. link Accessed 2/10/25.
Oliveira, P. E., P. E. Gibbs and A. A. Barbosa. 2004. Moth pollination of woody species in the Cerrados of Central Brazil: a case of so much owed to so few? Plant Systematics and Evolution 245: 41-54.
Van Zandt, P. A., D.D. Johnson, C. Hartley, K.A. Lecroy, H. W. Shew, B. T. Davis and M. S. Lehnert. 20019. Which moths might be pollinators? Approaches in the search for the flower-visiting needles in the Lepidopteran haystack. Ecological Entomology. 45: 13-25.
Walton, R. E., C. D. Sayer, H. Bennion, and J. C. Axmacher. 2020. Nocturnal pollinators strongly contribute to pollen transport of wild flowers in an agricultural landscape. Biology Letters. 16: 20190877. http//dx.doi.org/10.1098/rsbl.2019.0877
Wheeler, J. 2024. Moths are Cool Too. Xerces Society https://xerces.org/blog/moths-are-cool-too Accessed 2/6/25.
No comments:
Post a Comment