Triaenodes fly

Volovnik, Semyon V., 2025, Phytochory - the dispersal of animals by terrestrial and aquatic plants, Journal of Natural History 59 (21 - 24), pp. 1469-1539 : 1504

To fly or not to fly ?

The process of flying requires large and strong wings, powerful muscles, or long and thick hairs for the passive aeroplanktonic journey (like those of some caterpillars and larvae of scale insects). Nevertheless, the whole life cycle of some flightless insects occurs on free-floating plants ( Table 16).

Such wingless animals as soil nematodes are able to perform short (1 cm) seasonal migrations, up to a metre per year. But if they are inside the fragments of subterranean stems (rhizomes), they are likely to travel a distance greater than 100 km owing to wind and waves ( De La Peña et al. 2011). Thousands of semi-aquatic insect species disperse mainly as winged adults (dragonflies, stoneflies, numerous beetles, bugs and dipterans). However, owing to phytochory their water-dwelling larvae have additional possibilities for expansion, especially in lotic freshwater systems. A lot of them are transported by free-floating aquatic plants ( Center et al. 1999; Harms and Grodowitz 2009; Pavan 2010). Furthermore, 60–90% of immatures of shore flies Hydrellia sp. that developed in the tissues of floating plants are infested with parasitoids ( Deonier 1971). It can be expected that parasitoids drift within plants as well. It thus follows that wingless immatures provide additional chances to disperse.

Flightless passengers are common in coastal and island habitats. Seventeen of the 19 weevil species on the Haida Gwaii archipelago (North Pacific) are incapable of flight and some of them are associated with wood. It seems to be true that rafting played an important role in their colonisation of islands ( Anderson 1988b). It has been experimentally shown that the eggs and larvae of the wingless weevil Pachyrhynchus jitanasaius can disperse from one island to another inside fruits of their host plant ( Yeh et al. 2018). Additionally, the eggs of flightless Pachyrhynchus weevils can be transported by digestion in some birds ( Lin et al. 2021). Similarly, floating wood, seeds and leaves of terrestrial plants and marine kelps transport fragments of colonies of Bryozoa ( Willan 1979; Wood et al. 2006), and this is especially important for those lacking free statoblasts as ‘dormant bodies’.

Therefore, invertebrates with little potential for active migration can partially compensate for this via phytochory. It is the only method of long-distance dispersal for wingless invertebrates. Due to phytochory, bad fliers or swimmers, and flightless or sedentary invertebrates, can escape from density-dependent or distance-dependent mortality ( Goldberg and Trewick 2011; Vander Wall and Beck 2012, and references therein).