10 | MAY 2016
Mecysmaucheniidae spiders, which live only
in New Zealand and southern South
America, are drab and tiny spiders that hunt
for prey on the ground. However, a study
published in Current Biology(http://
tinyurl.com/hyg9ulv) has found that these
spiders have a remarkable ability to strike
their prey with lightning speed.
Lead author Hannah Wood of the
Smithsonian Institution’s National
Museum of Natural History says that theMecysmaucheniid family of spiders sit with
their jaw-like chelicerae open and ready to
snap when insect prey come close enough to
strike. “The high-speed predatory attacks
of these spiders were previously unknown,”
she says. “Many of the species I have been
working with are also unknown to the scien-
tiic community.”
While this kind of predatory behaviour
had been seen before in some ants, Wood
says it was unknown in arachnids. Further-more, Wood’s team estimated that this
high-speed, power-ampliied strike has
evolved at least four different times within
Mecysmaucheniids.
High-speed videos of 14 species revealed
a great range of cheliceral closing speeds.
The fastest species snaps its chelicerae more
than two orders of magnitude faster than
the slowest species.
In fact, the power output from four of
the spider species exceeded the known power
output of their muscles. Therefore, Wood
explains, the spiders’ movements can’t be
directly powered by their tiny muscles, partic-
ularly given the short times and small
distances covered during a strike. This means
other structural mechanisms must allow the
spiders to store the energy required to
produce such powerful movements.
The researchers have already described
some anatomical differences in the power-
ampliied trap-jaw spiders, but Wood says
they aren’t quite sure how it works and are
now conducting further investigations to
ind out.
In addition to providing new insights
into spiders and their evolution, the new
indings may also have broader implications.
“Studying these spiders could allow humans
to design robots that move in novel ways
that are based on how these spiders move,”
Wood says.Looking at the face of a trap-jaw spider.
The long chelicerae are in front and the
fangs are at the tip. Credit: Hannah WoodTrap-jaw Spiders Strike like Lightning
A series of massive supernova near our solar system showered the
Earth with radioactive debris, according to evidence derived from
radioactive iron-60 found in sediment and crust samples taken
from the Paciic, Atlantic and Indian oceans.
The iron-60 was concentrated in a period 1.7–3.2 million years
ago, which is relatively recent in astronomical terms, said research
leader Dr Anton Wallner of The Australian National University.
“We were very surprised that there was debris clearly spread across
1.5 million years,” Wallner said. “It suggests there were a series of
supernovae, one after another. It’s an interesting coincidence that
they correspond with when the Earth cooled and moved from the
Pliocene into the Pleistocene period.”
The international research team also found evidence of iron-
from an older supernova around 8 million years ago, coinciding
with global faunal changes in the late Miocene. The research has
been published in Nature (http://tinyurl.com/hwukuxs).
Supernovae eject heavy elements and radioactive isotopes into the
cosmos. One of these isotopes is iron-60, which decays with a half-life of 2.6 million years. Therefore any iron-60 dating from the Earth’s
formation more than 4.6 billion years ago has long since disappeared.
Wallner was intrigued by the irst hints of iron-60 in samples
from the Paciic Ocean loor a decade ago, so he assembled an
international team to search for interstellar dust from 120 ocean-
loor samples spanning the past 11 million years.
The irst step was to extract all the iron from the ocean cores and
then separate the tiny traces of interstellar iron-60 from the other
terrestrial isotopes using the Heavy-Ion Accelerator at the ANU.
The team found that it occurred all over the globe.
The age of the cores was determined from the decay of beryl-
lium-10 and aluminium-26 radioactive isotopes. The dating showed
that the fallout had only occurred in two time periods, 1.7–3.
million years ago and 8 million years ago.
A possible source of the supernovae is an ageing star cluster
that has since moved away from Earth. The cluster has no large
stars left, suggesting they have already exploded as supernovae and
thrown out waves of debris.Supernovae Showered Earth with Radioactive Debris