Great bug-count delivers!

Declaring victory after a nine-year effort, biologists have found 6,144 species of arthropods — insects, spiders and crustaceans (water critters like crabs) — on less than half a hectare of lowland rain forest in Panama.

Using technologies high and low, the entomologists swarmed over plots in the San Lorenzo Protected Area in 2003 and ’04. Their collection likely represents about one-quarter of the 25,000 arthropods on the 6,000 hectare (15,000 acre) reserve, says Yves Basset, first author of a new study in the journal Science.

Collecting and counting insects and their relatives may sound easy, but it’s not. For one thing, a major proportion live in the canopy, 30 or more meters above the ground.

The study plots in the Panamanian forest were sampled by spraying insecticide, climbing trees, floating in a hot-air balloon and even hanging from a giant crane operated by the Smithsonian Tropical Research Institute.

Each study plot was 20 meters square, for a total size of just under half a hectare.

Says the spider: Have we met?

A second obstacle arose after sample collection. Insects, spiders and crustaceans are poorly known, so 100-odd researchers spent years comparing specimens in museums, says Basset, an entomologist with Smithsonian in Panama.

When identification is complete he expects the new collection to contain hundreds — possibly thousands — of new species.

Why bother with the tedious task of surveying arthropods? Because it’s part of the overall quest to understand life, says Claudio Gratton, an associate professor of entomology at the University of Wisconsin-Madison. “One of the biggest challenges in ecology and biology is to understand the diversity of life on earth. But to answer this question, you have to know how many species there are. Surprisingly … estimates of species numbers range widely, from 3 million to over 30 million.”

The catch, Gratton adds, is that “Figuring out how many species exist is not easy. For starters, it is very unlikely that you will ever find all the species in an area,” so it’s necessary to “make an educated guess. This is further complicated by the fact that the longer you search, the more species you will find; the larger area you examine, the more species you are likely to find.”

And rare species, by definition, are harder to find.

The bottom line

Their overall calculation, that the 6,000 hectare reserve in Panama hosts about 25,000 arthropods, extrapolates to a global census of about 6 million arthropods. Handily, that jibes with previous estimates. “This is good news,” says Basset. “If we do our job well, we can recover a large part of the biodiversity.”

Indeed, comments Gratton, “In my limited knowledge of this field, this is one of the most comprehensive and systematic cataloging of the species of arthropods in a topical forest. The most striking finding was that after all their sampling, they were able to actually measure about two-thirds of the total expected species richness in the region.”

Intriguingly, the species richness was two to eight times higher than in a temperate forest, “far lower than many previous estimates,” the authors wrote. Forests in the Peruvian Amazon may contain much greater arthropod diversity, Basset says.

Can we throw it all away?

Insects play crucial roles in pollination and seed distribution, and even though the study advances the big picture, “it is also a reminder that we know very little” about arthropods, Basset says. “We have just provided an estimate of diversity in the forest, we know very little about these species.”

Time is a-wasting.

In 2009, one estimate said that about 32,000 hectares of tropical forest were destroyed each day.

“We know about 1 million arthropod species, but if there are really 6 million total, 5 million are unknown,” says Basset. “We need to hurry, because the forests where most of those are located are going to disappear.”

Image courtesy Roger Le Guen, copyright Panacoco, used with permission.

Raining bugs? Jürgen Schmidl fogging with insecticide in the San Lorenzo forest.