Where bees won't go: The unloved pollinators of the underworld

 

New research is showing just how much plants and crops rely on a host of darkness-dwelling creepy crawlies.

Think pollination, and you will likely picture a butterfly or bee flitting between flowers. But while these are indeed important pollinators, both the natural world and our food supplies rely on a host of other creatures, some of them decidedly less appealing.

Most of the world's 350,000 species of flowering plants rely on animal pollinators for reproduction. Pollinators and their importance for ecosystems are increasingly in the spotlight in recent years due to the dramatic decline in their numbers. Birds, bats, bees, bumblebees and butterflies have all been affected, with some populations shrinking by 80% or more. The causes include habitat loss, pesticides and climate change.

Scientists estimate that 3-5% of fruit, vegetable and nut production is lost globally as a result of inadequate pollination, affecting the availability of healthy food and threatening human health.

From cockroaches and beetles to the tiny "bees of the seas", here are some of the most unexpected, and occasionally disconcerting, pollinators the world continues to rely on – even if we don't always see them.

Cockroaches

Cockroaches are, in the words of one study, "among Earth's most despised creatures". But recent research suggests they play a beneficial and long overlooked role as plant pollinators – especially in the darker areas of forest often avoided by the world's more beloved bees and butterflies. 

Beetles

As soon as the first ever flowers unfurled from their buds in the early Cretaceous period, they were visited by pollinators. But those first soft landings on their petals weren't by bees or butterflies – instead, it's thought that the pioneers of pollination may have had six scuttling legs and tough, shiny shells. They were beetles. 

Beetles remain important pollinators to this day, often visiting flowers with the most seemingly unpromising allure – little nectar, greenish flowers, and an overpowering, possibly putrid smell, a set of traits known as "beetle pollination syndrome".

Moths

As they hover above wild tobacco flowers, hawkmoths unfurl their 8cm (3in)-long proboscis to drink up its nectar – among their favourite meals. As they do this, grains of pollen are also pulled – as if by magic – across air gaps of several millimetres or even centimetres.

This happens because, incredibly, moths collect so much static electricity whilst in flight that pollen is pulled through the air towards them. The fact that they don't need to touch flowers in order to pollinate them makes them very good pollinators. 

The majority of pollination research has tended to focus on day-flying insects, but researchers are now probing what is happening at night.

Bats

Bats are another oft-overlooked furry night-time pollinator. While most bats eat mainly insects, at least 500 plant species in the tropics and subtropics are pollinated largely by nectar-feeding bats. Scientists say that bat pollination (chiropterophily) could have advantages: their large size means they can transfer a lot of pollen at once, and they fly long distances compared with many other pollinators. However, the large size of bats can also make pollination by them energetically expensive for plants.

One example is the endangered greater long-eared bat, native to the south-western US and Mexico. It feeds mainly on the pollen and nectar of agave (used to make mezcal and tequila) and various cacti, hovering above the plants just like a hummingbird to feed. Along with the lesser long-nosed bat, it is the main pollinator of agave.

'Bees of the seas'

Despite their tiny, inconspicuous flowers, seagrasses are capable of reproducing with no help from animals. Turtle grass, for example, a seagrass which grows in shallow seas across the Caribbean, has miniscule, pollen-producing male flowers and female flowers which don't produce pollen. In coordinated cycles, the female flowers open, followed by male flowers, which release pollen into the tides after sunset.

A decade ago, it was widely believed this was the only way that seagrasses pollinated, with pollinating animals only visiting flowers that bloom in the open air. But in an experiment at an aquarium in Mexico in 2016, ecologist Brigitta van Tussenbroek from the Universidad Nacional Autónoma de México and her colleagues showed marine crustaceans were in fact playing a role.