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May 20, 1999

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Wekiu bugs-life on top of a volcano

"Wekiu" is the Hawaiian word for top or summit. This name was given to Mauna Kea's tallest cinder cone, which reaches 13,796 feet in elevation and is the highest in the Hawaiian archipelago. Life on the Mauna Kea summit must endure freezing temperatures, winter snow falls, and, occasionally, hurricane-force winds. The centers of the summit cones on Mauna Kea are permanently frozen to just a few feet below the surface. Only lichens and some mosses grow scattered on the tops of rocks. Until recently these cold stone fields were thought to be devoid of resident animal life.

An unusual new bug was first discovered in 1980 by biologists searching for insects under stones on Pu`u Wekiu. Although known to scientists as Nysius wekiuicola, this "seed bug" in the family Lygaeidae was given the common name "wekiu bug" to highlight the unusual location where these insects live. As their familiar name implies, most seed bugs feed on seeds by piercing their straw-like mouth parts into the inner seed tissue and sucking it out. However, since no native seed-bearing plants live in the summit area of Mauna Kea, it was clear to biologists that these insects must be tapping into a different food source than their close relatives.

Entomologists studied the ecology of the wekiu bug to find out how it could survive in such an extreme and hostile environment. Unlike their seed-feeding relatives, the wekiu bugs consume other dead and dying insects that get carried upslope by winds and deposited at the summit. The bugs search under rocks and across ash flows for fresh, wind-blown carcasses. They then use their piercing mouth-parts to puncture the exoskeleton of their prey and suck out the juices inside.

Wekiu bugs are nearly one quarter of an inch long with long, thin legs. Young bugs are dark brown with red abdomens, while the adult bugs are a more uniform dark brown to black color. Like all other true bugs, the young have only small developing wing pads. The adults, however, never develop full wings. Having extremely reduced wings may be an advantage to an insect that sneaks its way through rocks and ash. Besides, flying at the summit of Mauna Kea can send a bug on a long trip.

The bugs share their summit home with other arthropods, including spiders and caterpillars. Each has found its own way of dealing with the extreme cold found at this elevation. Wolf spiders hunker down under rocks that have been absorbing the sun's heat during the day. Moth caterpillars, like many other types of insects, have a sort of antifreeze in their bodies that prevents ice crystals from forming in their cells. Meanwhile, the wekiu bug takes the middle road. It also can endure subfreezing temperatures but prefers to find more protected retreats.

Until recently the wekiu bug was known only from the three cones at the summit of Mauna Kea. Construction of observatories at the summit of Mauna Kea raised concerns that the wekiu bug may be in jeopardy of losing its only known habitat. So the search began to find more bugs on Mauna Kea and the slopes of Mauna Loa. Individuals have now been observed on cinder cones nearly three miles from the Mauna Kea summit, while a previously unknown species was discovered on Mauna Loa.

The Mauna Loa bug, Nysius aa, was first captured in 1985 but not described as a different species until 1998. The life style of this bug appears to be very similar to that of its sister species, the wekiu bug, but subtle differences in its appearance make it clear that this is not the same species. Similar species have not been observed from Hualalai or Haleakala, but maybe they just haven't been found yet.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a network of tubes from the vent to the sea. Surface flows from breakouts of the tube system were observed on the coastal flats. Lava is entering the ocean near Kamokuna and enlarging the bench. The public is reminded that the ocean-entry area is extremely hazardous, with explosions accompanying unpredictable collapses of the new land. The steam clouds are highly acidic and laced with glass particles.

There were no earthquakes reported felt for the week ending on May 20.

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Updated: 3 June 1999