A headcount of arthropods, a group that includes insects,

arachnids and crustaceans, finds that these creatures outnumber

mammals — including humans — by a ratio of about 312 to 1.

The scrappy organisms also outnumber plants 17 to 1, the

study, published in the latest journal Science, suggests.

"There are different reasons to explain this," project

leader Yves Basset told Discovery News. "They are small and can make a living

out of nearly everything, including other arthropods, decomposing matter, plant

tissues, etc."

Basset also pointed out that often bug larvae don't compete with adults since they feed on different foos resources.

Basset is scientific coordinator of the CTFS Arthropod

Initiative at the Smithsonian Tropical Research Institute. To better understand

arthropod diversity, he and 102 other researchers looked for the organisms in the

San Lorenzo forest reserve of Panama.

Bugs tend to thrive in tropical

rainforests, but the population at this particular reserve in Panama is thought

to be average. The scientists chose to work there because the Smithsonian has a

canopy crane and other devices at the site that facilitate access to everything

from the canopy forest to the substrate below.

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Using this crane, inflatable platforms, balloons, climbing

ropes, and by crawling on their knees to get a better look, the researchers

sorted and identified 130,000 arthropods. These represented more than 6,000


By scaling up the diversity values obtained from twelve

other intensively sampled areas, the team calculated that the 23.2-square-mile rainforest

reserve harbors an excess of 25,000 arthropod species. These calculations, in

turn, contributed to the estimated ratios comparing numbers of arachnids to

plants and mammals.

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Basset thinks that these ratios hold true for cities as

well, and may even skew higher in favor of arthropods at urban settings.

"The mammal fauna in cities is rather depleted, but not

necessarily that of arthropods," he explained. "For example, a small urban park

may not host many mammal species, because it may be a too small area to

sustain species requirements, such as food and living space. However, let's say

you have 10 species of trees in this park, then they may well support as many

as 200 arthropod species, according to our data."

Humans tend to view insects mostly as being detrimental.

They can at times spread disease and destroy crops.

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"But we forget that these represent only a few species in

comparison to the whole of arthropod biodiversity," Basset said. "The majority

of insects live in forests and are responsible for the maintenance of these

forests via the different services of pollination, decomposition and herbivory.

In addition, many arthropods are efficient predators or parasites that suppress

the levels of herbivores."

Outbreaks of pests do not exist in tropical forests, he

pointed out, suggesting that arthropods help to keep ecosystems in balance.

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These organisms additionally "represent a formidable, but

untapped, reserve of DNA, genes and molecules — again about 20 times more

species-rich than plants from which we nevertheless get most of our

medications," he continued. "Who knows what may be concealed in these arthropod

molecules and how we could use them? We also need to discover most of these

species/molecules before they disappear from Earth."

This latest study and others indicate that we may be sharing

the planet with about 6 million arthropod species. Out of these, we only know

about 1 million, with the rest  and many

others possibly threatened by pollution, habitat loss, and other human-related


"In this context, I have difficulties understanding the

enthusiasm of the public for the search for extra-terrestrial life," Basset

said. "Are we not wasting dollars on a doomed quest, whereas with a fraction of

these funds, we could easily, as our study indicates, unveil a substantial

amount of the Earth’s biodiversity before it is too late?"

Top photo: Scarab beetle (Megasoma elephas, Dynastinae) in the understory of the San Lorenzo forest. Credit: Thomas Martin, Jean-Philippe Sobczak & Hendrik Dietz, TU Munich. Middle Photo: Dawn Frame and Alexey Tishechkin in the crane gondola netting insects attracted to flowers of

Nectandra purpurascens. Credit: Jürgen Schmidl, Laboratory Copyright: University of Erlangen.