St. Helens: Spiders, beetles were pioneers of new St. Helens

Following the eruption of Mount St. Helens, it rained spiders and beetles.

The spiders, carried in from surrounding areas by the wind, arrived at a rate of about one spider per square meter per day, according to Rod Crawford, curator of arachnids at the UW's Burke Museum of Natural History and Culture. However, unlike an eruption – something that's only happened two or three times in the last 200 years – spiders rain down out of the sky on a daily basis at Mount St. Helens and elsewhere.

Before Mount St. Helens, scientists had greatly underestimated the number, and therefore the importance, of spiders ballooning into an area, Crawford said. The blast from Mount St. Helens killed nearly all the resident spiders in the large area known as the Pumice Plain. The clean slate meant any spiders counted by scientists would have arrived on the winds.

From measurements made in the summer and early fall of 1983, scientists estimated that 2 million spiders fell per square mile per day during that time of year. The nearest likely sources for some species was as many as 30 miles away.

The wind also carried far more insects into the blast-devestated area than had been expected, according to John Edwards, professor of zoology. The classical view of succession begins with plants, followed by insects such as aphids that feed on plants, and finally, by predatory insects.

But predatory beetles and spiders were among the first to take up residence in the blast zone. The first true settlers –insects able to survive and breed on the bare surfaces – were tiny carabid ground beetles, 2 to 3 cm in length. These pioneers thrive in fresh devastation.

"They were the stars of Act 1 Scene 1 of the succession drama, and they disappeared off to some other bit of barren ground as soon as Mount St. Helens began to be clothed by plants," Edwards says. ¶